A question that keeps popping up is why don't any gasoline engines use compression ignition and higher compression ratios to be more like diesel engines. Well, Mazda is doing just that with their SkyActiv-X engine, and I've covered exactly how it works: ua-cam.com/video/yNSxow3W7ek/v-deo.html Hope everyone's having a great day, thanks for watching! Instagram - instagram.com/engineeringexplained/ T-Shirts - bit.ly/2BHsiuo
Here may be a good question for a video: could you explain the differences/benefits between a V8 diesel and an I6, and how those engineering differences impact performance?
@Engineering Explained, You said that complete combustion of Diesel occurs sooner. But the longer carbon chain of diesel needs more time to burn than petrol which has a shorter length. I have some questions regarding this. Can you kindly spare some time in answering them please?
It would be interesting to plot the torque over the entire 4-stroke cycle and show how this instaneous torque waveform (positive and negative) gets averaged-out by the rotational moment of inertia of the flywheel and combination of instantaneous torques from all the other cylinders.
I hear all the time that under-square engines (stroke greater than bore) produce more torque because of more leverage at crankshaft. However, a bigger bore would would result in the piston exerting more force. According to Pascal's law force is pressure times area.
With the advance of the EV with many having range extenders (generators only turning an electric generator), it would be nice to see what the ideal configuration for a constant speed or stepped speed generator engine. These engines will be the norm and not too far into the future.
Hey man, congrats on your great show, really enjoy learning from it. I was wondering if you could do a vid explaining what are rpms, and the fuction they do on ones vehicle. Would really appreciate if you did this, man. Thanks!
Another thing I didn't see mentioned was the fact that you can throw almost as much turbo as you want with a diesel because you're using compression ignition to ignite the diesel. You squirt the fuel in when you want ignition to occur (this is diesels "timing)", and can adjust the timing. In a gas engine obviously you cannot keep raising boost because you will get preignition. Weak links because headgaskets and studs...maybe EGT and Pyro turbo temps.
Stroke has a very significant affect on torque. If you take a rifle with a 28" barrel length firing a 7.62 NATO round and a single shot pistol with a 10" barrel firing the same round, you will have higher velocity from the 28" barrel. This has been explained as being due to the bullet spending more time with the power from the explosion being transferred to the bullet. The velocity and corresponding muzzle energy is far greater in the rifle, even though they are both using the same amount of powder.
Another great video! Maybe you could make a video going into further detail on why diesel engines do not necessarily require a throttle body and why the newer diesel engines do have them but for what purpose?
I like your explanations. This one got confusing going from the diagrams in #2 to the ones in #3 because you switched the order. #2 shows gas then diesel, #3 shows diesel then gas.
3:33 i expected to see these numbers a little closer to equal. 3 x 50mm x 50mm x 80mm (volume of a cylinder) = 600,000 for the gas, 3 x 40mm x 40mm x 120mm = 576,000 but changing the 120mm stroke to 125mm makes these two engines equal instead of just close. 3 x 40mm x 40mm x 125mm = 600,000. i dont know why i paused it to double check. just food for thought.
Nice. You must be right, but here is some things that makes the difference. I think that only thing that really makes the significant difference between gas and diesel engines torque is turbo. Turbo or other charger. If you compare gas and diesel engines whitout any chargers, usually the gasoline engine makes more torque at the same volume. And if compares gas and diesel engines whit chargers, there must be charger on gasoline engine too and same boost. energy capacity of fuel does not make any difference to power. It make's difference to fueleconomy. Because it is no problem to inject more fuel to engine. problem is to get enaugh air to the engine. If compared methanol and diesel, it is possible to make more power from the methanol, even if there is much less energy at some volume.
Well actually main disadvantage of diesel engine is that it cannot reach gasoline engine's rpm. If we want to compare gasoline vs diesel, we should always consider turbocharger. If we think of gasoline turbocharged engine, does it lose at torque? Power to diesel???? I agree with power density, lean burn and so on : they are the reasons why diesel engines are more efficient. But it doesn't means that diesel engines have more torque AT ALL.
Diesels never USED to have more toque than an equally sized petrol engine. At least not until turbocharging and intercooling became the norm. I remember when you could buy naturally aspirated diesels back in the 80s and 90s and they had no torque to speak of, they just gave what little they had at a very low RPM, making them very economical on fuel. I'd wager that a gasoline engine, when boosted to the same degree as a contemporary turbo diesel of the same size, will actually put out about the same torque and considerably more horsepower, thanks to its ability to rev higher. Take for example, the VW Golf GTD and Golf R. Both 2.0 engines, Both are turbocharged and intercooled. Both have around 280lb/ft of torque from around 1800rpm. But GTD has 184hp, at 4000rpm, R has 296hp at 5600rpm.
Some people are natural teachers and love to impart their knowledge. Too bad in most countries teachers salaries are so bad, otherwise more people with the actual calling and ability would take a teaching job
@@svarthofde2492 it's not only salary, many of them can't do what they would want to because education is very strict and systematical, they're getting fired and getting harassment in their address, basically a dead system that still exists, ignorant parents who only care about their children graduation and grades and not their knowledge doesn't help either
A couple of things...if I remember my reading correctly, you have #2 backwards. It's gasoline that ignites (and burns out) almost immediately, the moment the spark plug fires. In a diesel however, fuel keeps getting injected until 20-30 degrees past Top Dead Center (TDC) on the power stroke, maintaining pressure for much longer. The reason this is important, is that when a piston is all the way up (at TDC) it produces little to no torque, the crank pointing straight up and being virtually in-line with the connecting rod. It's only when the crank has turned that the connecting rod can push against its side, creating torque. By that time, pressure in a gasoline engine has already dropped considerably, which is why you really have to hit the gas to tow anything with a gas-powered truck. As for turbos, gas engines have their boost limited by the octane level of the fuel. As a gas engine compresses both gasoline vapors and air, too high a boost will result in detonation upon compression. In a diesel you're just compressing air, the fuel isn't injected until compression is complete. So, the only limit on turbo boost in a diesel is the strength of the engine itself--which is WHY they're built so strong.
Thanks for the comment. I don't have enough background to fully understand the first paragraph (sort of half get it) but the point about diesel turbos is clear even to me.
I thought about this crank angle thing (because other people mentioned it too) for a while and I think a lot of people missunderstand how pressure works. If all the fuel is combusted immediately higher initial pressure will be created in the chamber. If the fuel is combusted slower then the chamber will start with a lower initial pressure but decrease slower because some of the fuel will be burning and counteracting that pressure loss. If as you say it would be best for the fuel to burn at the best crank-lever angle then gasolines engines would fire the spark plug then, which they dont do, most even advance the timing of the ignition before TDC.
Gasoline has a flame front, a spark plug initiates the flame which travels. The diesel burns everywhere at once because there’s no one single point where it has to start.
I'm studying thermodynamics in college, first I watched an old video about the difference between gasoline and diesel engines, and somehow I ended up watching a tons of your vids. So interesting, love the way you explain everything!
@@Kit_Bear What a poor attempt to label oil companies as the problem. Environmentalists are the ones pushing against anything that burns hydrocarbon fuels.
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Electric cars are the future, almost present, but believe me there will be Diesel on the road.
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@@haliax8149 I'm an enviromentalist and I love diesel :-). There aren't and won't be in the near future a combustion machine more efficient and reliable than diesel.
Jason, great video. But I have a different take. Diesel fuel is an "oil" and burns SLOWER than gas. This is why diesels cannot create much horsepower; beyond about 4000 rpm the diesel piston is literally "running away from" the expansion of a slower combustion rate. But because diesel burns SLOWER, combustion reaches peak expansion LATER -- when the piston is LOWER in the cylinder. In your video on "torque vs. horsepower" you do a good job of explaining that Torque = Force X Lever Length. At Top Dead Center and Bottom Dead Center the effective "lever length" of the engine crank is ZERO. So during combustion, lever length (torque potential) starts at zero, rises to maximum as the crank turns and the lever length increases, then falls back to zero. In a "standard" gas engine (normally aspirated, square bore, decent compression ratio) peak combustion pressure is reached at ONLY 15 DEGREES OF CRANK ROTATION (midway between 1 and 2 o'clock, on a clock.) This is because gas burns quickly. But at 15 degrees "lever length" is VERY short. Torque is minimal even though combustion pressure is highest at this point. As the piston descends cylinder pressure DECREASES (because volume INCREASES.) That "typical" gas engine has its best "mechanical" torque potential at 72 degrees of crank rotation (which added to 18 degrees of conrod angle = 90 degrees. Best torque is created by pushing on the lever at 90 degrees.) But that "standard" gas engine develops peak torque at ONLY 42 DEGREES of crank rotation, because this is the best intersection of rising mechanical (torque) advantage and decreasing combustion pressure. After 42 degrees, combustion pressure drops so rapidly there's too little pressure to take advantage of the better mechanical advantage that exists at 72 degrees (the "longer lever" moment.) But because diesel burns slower, it reaches peak combustion pressure when the piston is at a LOWER point in the cylinder, where there is a greater mechanical (torque) advantage. So, diesels create higher torque, but produce very little horsepower because diesel burns too slow to keep pushing the piston faster and faster. (And this is why the torque/horsepower curves of a diesel engine "cross" at much lower rpm than gas engines.) Gasoline burns so much faster, it can "push" an engine to higher rpm, and since (as in your "torque/horsepower" video) power is the SPEED at which work is accomplished, gas engines develop higher horsepower. But less torque because they create peak combustion pressure at a less advantageous (earlier) crank angle than diesels. However, since gas engines can rev faster, they can generate more of these "peak moments" per revolution of the vehicle's wheel. So they accelerate faster, have a wider useful rpm band, and don't need as many gears to move a vehicle to a high top speed. Incidentally, the difference in "burn speed" between gas and diesel sheds light on why a super/turbocharged engine develops more power. Not only does it raise the temperature (higher thermal energy) it raises the compression ratio. Higher compression ratios cause the burn to take LONGER to complete. Meaning there is higher combustion pressure when the piston is lower in the cylinder, where there is more mechanical (torque) advantage. This is a big part of the reason why super/turbocharging either a diesel or gas engine increases its power. Sorry for the long comment. Hope this is useful...
I'm on board with this, the diesel is getting much of it's torque from the stroke length and good for you for pointing out that with the slower burn that there is most certainly a HP limit. Just another note diesels were not always turbocharged. Although sure your getting some torque increase from turbo charging diesels they really put turbo's on to get the HP up there, e.g spin them faster. A current CAT bulldozer is still turbo because why not take the extra torque but they were looking for the HP as that means you push more dirt around in a given time. Same for hauling freight on the highway, increase the HP and you can pull the load faster and get paid more. If you drive a diesel often, you will notice they mostly never "lug". They always have extra torque on hand.
I agreed with everything in your comment right up to the point where you said that higher compression slows the burn rate. I'm sure that is not true. In fact, in a gasoline (or any spark fired fuel) engine it increases the speed of the burn. This is why higher compression is necessary for extremely high rpm engines. With lower compression the burn rate hits its max at a lower rpm and will not push the piston faster. To make an engine that will run at 8000 rpm you must increase both air flow AND compression. With diesel, turbocharging increases cylinder pressure, increases the amount of oxygen in the cylinder, and allows the injection of a lot more fuel. It's the additional fuel that creates more torque. I agree that higher pressure when the piston is lower in the cylinder is giving the high compression engine more power. But the piston must be moving a lot faster too for this to work.
@@michaelcooley8275 You're totally correct, higher compression doesn't slow the burn rate. A volatile gas expands FURTHER when it explodes if it has been compressed more before combustion. So it takes longer to reach full expansion which means there is more combustion force when piston is lower in the cylinder, where the torque from a superior crank angle is better. If I said the burn rate is slower I spoke incorrectly. Good catch.
One of the few channels ran by a youth who's able to properly explain the automotive world in detail! I'm a mechanical engineer too and this is how these kind of topics should be explained! Too easy to test drive expensive cars only because you have a lot of money and saying things that everyone would be able to notice only by reading a brochure. As always can't wait for the next video! Thanks Jason \m/
Very nice video. The way you explain things is just amazing. I am 19 year old kid who is about to join college. And I am incredibly passionate about cars and engines thats why I watch your videos.....
Great video as usual! I would argue that in a Diesel engine complete combustion does not always occur right away. You make it sound as if the fuel is injected in a quick shot and bam, it’s all instantly burned up just after TDC. The duration of injection or number of separate injection events per power stroke depend on the amount of fuel needed to be injected which is primarily determined by engine load. At idle a small quick shot of fuel may be all that is needed to keep everyone happy, but obviously when pulling 40 tons over a mountain the engine will require a lot more fuel. What I was taught is that one of the beautiful things about a Diesel engine, and one of its main torque producing characteristics, is that it can continue to inject fuel and burn it throughout the entire power stroke. In convention gasoline engines a given amount of fuel and air is drawn into the cylinder in response to a given load, what’s taken in is what you get and as it burns during the power stroke the amount of downward force drops off as the fuel is used up. A diesel is capable of continuing to inject fuel throughout the stroke and will therefore maintain the downward push the whole way down, equaling more torque. Take a look at how a normal inline injection pump meters fuel with its port and helix set up. At light load there is only a small amount of the helix exposed which means that a small amount of fuel will be injected, but the plunger will still make a full stroke, so it would still be injecting fuel during the power stroke if it had been given it. As load increases more fuel is metered in and then injected, not all at once, but throughout the power stroke.
I came here to say this. This is called the “Cutoff Ratio” and has become electronically controlled in common rail diesels. The classic diesel thermodynamic cycle maintains constant cylinder pressure throughout the power stroke, achieved in practice by continuing to burn fuel as the piston descends and the volume increases. This means that a diesel piston is still being pushed down with the same force when its (longer) crank arm is at 90 degrees. THAT’s where the stump-pulling torque originates. (Great channel.)
Also: common rail systems can control the rate of fuel delivery by modulating the rail pressure, so the fuel dose can be delivered quickly at high rpm and high load, or drizzled more slowly at lower load or rpm. My CDI’s rail pressure varies from 4500psi at idle to >22,000psi at full load. By electronically varying the timing and duration of the injection event for a given fuel dose the engine module has good control.
Thanks for answering a question I always wanted to ask, but could never find anyone to properly answer. That has always befuddled me about diesels, and their amazing way of producing gobs of torque.
I appreciate a lot your work: it's great, keep going! Unfortunately I have to say something about the topic of this video: First of all It's true that Diesel engines have higher compression ratios resulting in higher Peak firing Pressures and consequently higher values of torque BUT this is not the "true reason" why CI engines have more torque COMPARED to SI ones. In fact, while the SI engine works always stoichiometric (or even slightly in the rich side (relative A/R (Air Fuel ratio) ~0.9)), the Diesel engine cannot work anywhere close to the stoichiometric A/R due to t bad air utilization (min relative A/R is in the order of 1.2-1.3) thus resulting in ~20% less fuel injected (in mass) for the same quantity of air in the cylinder. Lower fuel injected means lower energy released in the combustion and so lower torque (this "base" 20% deficit is partially, but non totally, compensated by the higher compression ratio and higher Diesel specific energy). If you compare the torque figures of old naturally aspirated diesels with NA SI engines of the same time you'll verify what I'm saying. The second thing you mentioned is not wrong but it's not that relevant: the combustion of a Diesel engine is more efficient when it tends to a constant-volume combustion (like in the case of the IDEAL Otto cycle). For partial loads, the actual duration of the two combustion processes, even if they're fundamentally different, is comparable and I would say that there are so many variables involved (speed, temperature, fuel quality, turbulence in the clinder, etc) that is difficult to say which combustion process is the most efficient. However, at high loads, the combustion process of a SI engine is definetly occurring faster than a CI one since the latter has to fight against a "mixing controlled combustion" during which fuels struggles to find air to react with. (In fact, CI engines rotate slower than SI ones) For what concerns the third point you presented... it's just a false myth: the higher lever of a longer stroke is counteracted by the lower force resulting from a smaller bore. If you take the condensed formula to compute engine power you'll notice that bore and stroke are multyplied together giving as a result the displacement (longer stroke -> smaller bore). So, the reason why diesel engines have much higher specific torque than SI ones is turbocharging. Thanks to the very high allowed boost ratio it is possible to force a lot of air inside the cylinder and so it is possible to burn more diesel than gasoline (for a given displacement). This results in a much higher torque together with a more efficient engine. (Power output, unfortunately, si affected by the "slow" combustion process that doesn't allow the engine to rotate as fast as a SI engines). This comment doesn't want to be against you. You've always done a great job. It's just to make things a little bit clearer.
Diesels also have much stronger internals resulting in more spinning mass within the engine which helps with torque. If you lighten the internals in a gasoline engine, you'll gain power but at the sacrifice of torque.
Jason I'm your fan but that was not the best movie you did. Federico pointed out why in very good and informative post above. Remeber your movies are also wached (with pleasure!) by professionals. :-)
I'm curious about one of your last statements. "Power output, unfortunately, is affected by the "slow" combustion process that doesn't allow the engine to rotate as fast as a SI engines)." My question is, doesn't the combustion process happens quicker on a Ci engine than in a SI engine? As was explained in the video, (or how i think it was, and how i have interpreted) the burning process of a diesel engine happens in slightly faster instant than petrol. And another question, when comparing both CI and SI as turbocharged engines, is it expected to the SI engine have more torque (and?) horsepower? Thank you in advance if you answer! :)
In SI engine fuel is injected during intake stroke. It has time during intake stroke and then majority of compression stroke to vaporate and form proper A/F mixture. There is no such a time in diesel. In diesel fuel burns once its injected but injection itself takes some time thus crank angle rotation. Moreover at high loads mixture is too reach right at the injector nozzles and it needs some time to mix with air to burn. Thats why you see black smoke in diesels under load. They don't fully burn fuel. All in all diesel combustion takes longer then gas at high loads.
I don't know if you've mentioned this in other videos, but the implications of piston speed: A higher piston linear speed means that the peak force experienced by the connecting rod will be higher and thus the connecting rod must be stronger in order to withstand this force. (This also applies to the wrist pin, the piston itself, the crankshaft etc)
complex topic. Would be interesting but this is closer to chemistry than engineering. :) A simplified answer from me (not an expert) would be ethanol has less energy than gasoline but burns hotter and faster (cleaner) allowing for you to pump more in at a time to make up for the energy loss. High ethanol fuels can overheat an engine or burn out seals on an engine not made for it. Unless technology has changed -- which is very probable -- it used to take 1 gallon of gasoline to produce 1 gallon of ethanol so it was more of a waste of time for anything other than performance engines like F1 or NASCAR vehicles.
acephantom903 I live in Brazil and here we have flex fuel engines for over 30 years. Nowadays more than 90% of veihcles sold each year here are flex ones. Almost every gas station here has pure ethanol (94% actually) pumps. Most flex engines here can produce more torq and power from ethanol than gasoline. In many parts here is cheaper to run on ethanol than in gasoline.
That is interesting. I wonder how you have ethanol so cheap. Maybe it isn't that the ethanol is cheap but the cost to import gasoline is high? Flex fuel engines are made to handle to increased heat while normal gasoline engines can handle a max of 20% ethanol before it gets dangerous. Because you have such high ethanol contents, your car's computer can see that and can increase fuel injection to give you stronger power than gasoline as it doesn't need as much air while combusting. Do your flex fuel vehicles also have a setting to increase fuel efficiency when running high ethanol rather than higher power? It would only be a computer setting change to have the different modes.
Fernando Sousa ... iirc...it takes 30% more ethanol to get the same energy output of gas. Ethanol also is higher octane so lots of turbo guys like it for high boost.
The true reason most diesels make more BMEP is as follows: 1) They do not suffer from detonation or pre-ignition, meaning an ultimately higher Cylinder pressure and temperature is possible. (a gasoline engine would need to be run on a very high octaine fuel to produce the same BMWP without damaging abnormal combustion events) 2) Compression ratio. An engine is a thermal device, ultimate efficiency depends on compression ratio. Higher CR = more BMEP 3) Average cylinder surface area during combustion. Again, DI engines burn their fuel at lower average combustion chamber volumes and hence lose less heat to the chamber walls. More heat = more pressure = more BMEP In all cases the charge burn angle is calibrated to position the peak pressure point at a geometrically optimum point in the stroke. For most engines (typical geometries), this is around 10 to 15 degCA ATDC. In a SI engine this is done by optimising the ignition angle (where the spark occurs) and for a DI engine by optimising the injection angle and injection mass profile. Modern DI gasoline engines are now actually pretty close to diesel engines in terms of maximum BMEP, but can produce significantly more ultimate power as they don't suffer from the same burn rate limitation as a diesel that limits the practical speed for peak power to around 5krpm
When they used Diesel engines in LeMans racing (Audi and Peugeot) even these racing engines have the max power around 5000 Rpm. And the reason is exactly you stated that the burn velosity restricts higher RPM. A follow up video would be nice, since I think there is some confusion here.
I actually did some combustion development and port optimisation for the Audi R10 TDI LeMans engine, and ultimate burn rate was the power limiter that drove the engine design towards a high BMEP, low speed, low friction type architecture! Add in the mandatory air restrictor and it was always going to be a engine dominated by it's combustion efficiency rather than combustion power!
Amazing comment better than the video ! How are the new gasoline engines get torque as a diesel counterpart, but more power and they have quite good economy too ?
Hi Jason - Nice video. It would be interesting if you could do a segment (if you have not already) on how engine designers create an engine for more or less torque, along with how they control what RPM that torque reaches its peak. Obviously your video touched on some aspects of what influences torque; it would be interesting to list all the variables and their trade-offs versus each other. Thanks.
Well, there is actually only one reason that diesel engine is PERMITTED to have more torque than gas engine, and that is because diesel engine is built much tougher than a gas engine in order to handle more torque. Diesel engine has a slower combustion process therefore cannot produce torque at high speeds, so to make up for this, it must have higher torque at lower rpm to compensate for the lack of torque at higher rpm. Gas engine is designed to be light, plus risk of detonation at lower speeds with higher loads, therefore is NOT permitted to have high torque at slower speeds, because it will self-destruct. At higher rpm, gas engine cannot complete its combustion until the piston is halfway down, therefore cannot impart all of its combustion energy to the piston, so its peak torque is lower than that of the diesel engine that is ALLOWED to burn more fuel at lower speeds due to the lack of detonation risk, but that's by design only. Theoretically, a diesel and a gas engine burning the same quantity of fuel per stroke at low rpm at which complete combustion happens early in the piston downward stroke should have similar torque...but of course, in real life, the gas engine is NOT allowed to have its peak torque due to its lighter construction and the risk of detonation at lower speeds with higher loads.
Diesel burns MUCH slower than gasoline, which helps it push on the piston for a longer period, taking advantage of the longer stroke... That, is why they have more torque.
Of course! To put in layman's terms, when you combust fuel past top dead center you are effectively reducing the amount of possible work you can get out of it. Fuel that has been burned at the beginning of the the power stroke will have more of its energy extracted out as work (torque). This is mildly similar to how a higher compression ratio will result in more power output. Injecting fuel late (and therefore igniting late because we are talking about a diesel engine) is reducing the amount of work the fuel could have done. Obviously this is inevitable because diesel engines can't inject fuel instantaneously, but it is in no way beneficial. Does that make sense?
Brady Black Makes perfect sense. If you ignite the fuel when the fuel is compressed to as small space as possible (TDC) it gives more powerful expansion compared to igniting later when it would produce less force
Kinda. So the pressure IS higher (I think thats what you mean by a more powerful expansion), but it is also that the force exerted on the piston is being over more time (more crank angle degrees).
cuz torquie supercars are no fun when they are 500hp vs the fancy neighbours 707hp gasoline car, so no bragging rights wich makes them some what useless jokes aside its as simple as that theres no braggin rights for the PR people to work with in a supercar/muscle so their job becomes a nightmare and people dont seem to care about diesel, let alone all that people that think diesel is the nastiest stuff in the world
I think it has to do with the lower rpms associated with the longer stroke length and heavier components. They have more torque but can't rev as high so in the top end gasoline ends up with more power. (I think, I could totally be wrong.)
diesel has lower HP than gasoline in same displacement. for comparison, the 2.5L turbo diesel produce 180 HP while 2.5L turbocharged gasoline engine can reach 270 HP. I heard that furthest speed that diesel car can reach is 177 mph, while gasoline now is 278 mph.
But gasoline engines run on the Otto cycle which has a constant volume heat addition straight line on the graph. This represents gasoline burns much faster than diesel. And diesel cycle has constant pressure heat addition.
Diesel does burn SLOWER than gasoline, that's why they can't rev that high... NA diesel does not have more torque than a NA gasoline. The higher CR AND turbo (and multijet) gives higher torque. Turbocharge a gasoline and torque is there as well. Diesel efficience is higher due to higher CR (higher thermal efficienty) and higher BTU/volume compared to gasoline.
You are aware that you are contradicting everything he says in this video? Diesels can't rev that high due to longer strokes and higher piston speeds relative to rpm and diesel fuel burns quicker in an engine, almost instantaneous as it uses the heat created under much higher compression. @@ivojanssens221
@@Leemur2335 no way! Diesel engine sounds like the chain of many explosions but gasoline one doesn't. Just think, why? The answer's simple - combustion at diesel engine is the fast explosion. Not the same, and gasoline combustion flows very slowly in one cycle.
Do not agree with your suggestion that diesel has a faster speed of combustion. In fact diesel fuel burns more slowly in the engine because it is being sprayed into the cylinder with the injector over a considerable portion of the piston down stroke. In fact the ideal is to produce a constant cylinder pressure as the piston descends and this is the main reason diesels have higher torque. With a gasoline engine the spark determines almost instantaneous combustion with very rapid flame progression at the top of the piston stroke and the pressure falls off rapidly with the piston descending. Clearly this will produce lower torque. Dan Hanlon.
This is true. This is also the main reason why diesel engines can't rev past a certain point. Depending on stroke length, the theoretical limit can be anywhere between 5.5 and 7000 rpm. For most engines, it is around 6000 rpm. If you exceed this limit, you will still have considerable expansion when the piston hits BDC, grenading the engine.
You dont understand basicaly physics! please compare without turbocharger > and same displacement (not compate 1.4L gasoline with 1.9 tdi with turbo) for example> 2.0FSI have bigger torque than 2.0 Sdi 16V , please dont compare gasoline engine without turbo with diesel engine with turbo... Its ABSOLUTE TRUE > ENGINE with more air have more torque, but with same air comsume have gasoline biger torque... Exist (BOBA racing, AME racing and more users 800HP+) turbocharged gasoline engine have with 2.0L 1000Nm and more than 1000HP and exist evo 2.6L have 2500HW...diesel with same displacement end about 450-500HP on clear diesel, yes its exist more but with NOS or methane injection but still less than 1000hp on 2.0Tdi
Guy basically said diesel fuel has %10-15 more energy in it and youre trying to say gasoline car has more torque in same condition is kinda funny. Diesel engine doesnt have more air inside the piston because of only turbocharge, it has more space ! Same amount of fuel, more air, more energy in fuel will result as more torque in same conditions. Jeez dude ...
Erm, probably the most important part would be the turbo on the side. A non turbo diesel (aka NA diesel) has very little torque compared to equal sized petrol engine. So obviously it is the turbo. Sure, a turbocharged petrol will not make as much torque as a diesel from factory, but then it has the rpm benefit. A 2.4l 6 cylinder diesel with no turbo makes less torque than an 8V 2.3l 4 cylinder.
Look at the Nissan Patrol from the 90's. They have a 4.2L naturally aspirated diesel (TD42) and a 4.2L naturally aspirated petrol engine (TB42). The bore and stroke are identical on both, yet the petrol produces 15% more torque and 30% more power at only 200 rpm more. I realise this is a one off but it's a great comparison of engines with identical bottom ends which eliminates the bore and stroke argument.
Reason why dragster snatches 6.2 Chevy diesel engine blocks and throw on gas heads and use electronic ignition because the blocks are the same there just beefier! then supercharge it or turbocharge it and crank up the boost!
Your math is wrong. You were supposed to compare torque/fuel, not torque/engine_configuration TB42 is a fuel monster, while TD42 consumption is decent for its performance.
Bore / Stroke doesn't affect the torque - Consider 2 engines have the same volume and pressure. One has 2times the stroke but only half the piston area. You get 2 times the distance and half the force.
No, you will get more torque because of the longer arm of the crankshaft. But you'll get less horsepower because it can't rev as high as the short stroke engine.
Bravo, at least somebody understands physics and mechanics. Most of the posts and comments on here are just wrong, and the frightening thing is that people with no technical insight blindly accept it.
The stroke length is very important for more torque and your illustration shows it quite clearly. In order to have a longer stroke, the crankshaft has to have a larger offset to the connecting rod in order to move the longer piston stroke. That larger distance means that the piston is in effect pushing the crankshaft around using more leverage. It's like using a longer wrench to loosen a stuck bolt. The larger offset the crankshaft has is like the longer wrench.
USWaterRockets But.... If you keep the same capacity of the cylinder then longer stroke means smaller bore and piston area thus force pushing piston down. All equalizes. ZERO effect on torqe. Jason simplified it too much imho.
Sewer Razus Correct. Longer stroke with smaller bore means lower stress of the components, provided RPM is not too high. Since area is dimension squared, halving bore diameter means quadrupling stroke length to get the same displacement. Force on the piston is area times pressure, area is one quarter so it's quarter the force. Torque on the shaft is force times crank length, so that's quarter the force and quadruple the length. All comes back zero. And why wouldn't it? The compressed combustion products make certain amount of mechanical work by expanding to certain volume. This means this amount of mechanical work will go to the shaft, no matter the bore and stroke configuration.
The thing he missed is that the diesel injection and so its burn duration is longer, so the cylinder pressure is held constant as the piston descends. This means the combustion pressure is still at its maximum when the crank is swinging past the 90’ and the piston has its best leverage. A gasoline engine has lost a significant amount of pressure by the time the crank swings through 90 degrees, so the piston isn’t generating the same torque.
Part of diesel efficiency is its lack of a throttle body. It always fills the cylinder with air, it varies the power output by varying how much fuel is injected. If you’ve seen a truck with just a hint of black smoke under load, they are running about as powerful as they can without wasted fuel.
I’m sorry to say he did not explain it. He was also wrong regarding literally almost every reason he gave. There is one reason: Diesel engines don’t have to worry about knock and or pre-ignition at low engine speed like gasoline engines do. You know how on modern turbo gas engines how the middle part of the torque chart is flat? That’s a limitation to avoid knock. High pressure, high temperature, and ample time mean that the combustion would not proceed as desired if the boost pressure wasn’t reigned in.
@@francoismorin6806 C'est vrai que maintenant les voitures diesel sont toutes équipées de turbos mais par exemple une xantia 1.9d de 94 faisait quand même 70cv pour 123Nm ce qui est pas mal du tout comme ratio
@@J0riS bien sûr que c'est pas mal mais avec un 1.9 essence on peut sortir 190ch et 190nm assez facilement par conséquent selon moi le titre de cette vidéo est faux 🙂
Excellent video that explains things very well, but perhaps It's also worth mentioning that although diesel fuel is more energy dense, it has a slower burn rate than gasoline, which imposes a limit on the maximum rpm at which a diesel engine can continue to produce power. That comes out at only around 4000rpm, and there's nothing to be gained by designing the engine to spin faster in order to do more work because the fuel won't be able to burn fast enough to keep up with the shorter compression/ignition cycles.
LOVE IT!!! Thank you for the killer, straight to the point vid with some GREAT visual aides!! I'm sure this was not quick and easy to put together!! (well, at least not QUICK...most likely quite easy for that brain of yours my friend!!) :-)
You touched on all the right points, however, Diesel engines do not burn evenly nor completely as you stated, the combustion in a Diesel is a Heterogeneous one , when fuel is injected, the outer part of the spray burns lean while the inner does not and takes longer to combust, secondly I expected you to expound more on the importance of no throttle body in a diesel, rather than generalizing it as pumping losses, the more technically correct term would be Higher Volumetric effiency as a result of no throttle body
Doesn't take as long, but you can (if you want to make more power) continue to inject fuel during the combustion stroke with diesels. Not efficient, but you'll make more power and it will appear to burn longer (though really it's just a continuation of fuel injection).
This is what I was taught by instructors while taking diesel technology courses. The torque output has a direct correlation to fuel timing. Because of the slow burning nature of diesel fuel, during the power stroke it can be injected into the cylinder after top dead center.
That's true which is another reason it's more suitable to a long stroke low revving engine to take full advantage of it and the fact that diesel fuel has more like 30% more energy per gallon than gasoline, not 15% as he stated.
EDIT: ELI5 : Petrol engines rev higher, delivering reasonably constant torque combined with ascending power output over a wide range of RPM rates (typically 1500 to 6-7000rpm) whereas diesels will achieve peak torque at lower rpm and have a much narrower band of revs across which power ascends (say 1400 to ~3500 rpm). This essentially means that a petrol vehicle will be able to accelerate (and decelerate) more in each gear before having to change. This makes a for a much more flexible driving experience as it allows one to (eg) hold one gear between two corners while a diesel might hit it's rev limit and get "bogged" down forcing a change up after the first corner and subsequent change down before the next. As each gear change effectively loses a bit of time due to the drive not being engaged it's a less "sporty". Diesel engines are also heavier as they can't be made of lightweight alloys.
@@hoshigakip Thank you for the crisp response. Very interesting piece of knowledge..I will remember this whenever I watch WRC or F1 or MotoGP next time :D
WEIGHT. weight is arguably more important than power. weight affects acceleration just like horsepower but it also affects cornering, handling, braking, and many other areas also. lets relate the extremes. a motorcycle for speed and a semi truck for towing. the added weight of putting a diesel in a motorcyle would be counterproductive the better fuel economy would be dwarfed by nobody wanting such a heavy machine. and using a gas engine in a semi truck wouldnt be efficient enough for such a heavy weight. sports cars are closer to motorcycles than semi trucks.
Diesels actually DON'T make more torque. They are better suited to forced induction, that's all. If you compare any production naturally aspirated diesel VS petrol from the same manufacturer and time period you will see that petrol engines make more torque and much more power ie. Mercedes OM606 3L diesel 136hp, 210Nm torque, M104 3L petrol 220hp, 310Nm torque
Couldn't you just build a gasoline engine the same way diesel engines are build (Besides the higher compresion of course)? So wouldn't it then have the same benefits the diesel engine has?
But Diesel engines don't produce more torque, not with the same charge they don't. A turbocharged diesel engine running 30PSI produces more torque than a NA gasoline engine of similar displacement, sure, but slap a turbo on that gasoline engine and then tell me something about torque. It's also a myth that torque has anything to do with stroke. You do not find any correlation between stroke and specific torque, engines of similar displacement and very different stroke length produce the same torque. A Chevy LT1 with 3.62 inches of stroke produces 75 pound feet per liter, a Yamaha R6 with its puny 1.67 inche stroke produces almost exactly the same specific torque (actually even more in fact because of a higher compression ratio). And this can be easily explained: while stroke increases the lever arm to produce torque at the crank, the force on that lever arm comes from the in cylinder pressure, and force exerted by a fluid over a flat surface is pressure*area and an engine with more bore has a larger area. So you see for the same displacement if you increase stroke and reduce bore you do not actually gain any torque as what you gain in lever arm you lose in the force actually being generated on the piston and sent through the con rod.
If that were true all trucking companies would switch to gasoline engines tomorrow. Gasoline is about 50% cheaper than diesel fuel and fuel is the greatest expense of running a truck.
Excellent lecture, thank you. Makes me sad that I’m giving up my 6MT TDI Golf and have decided on the gas-driven NC Miata for cruising. I’d love a way to replicate that low-torque push for an MX-5 and get real efficiency. Diesels are awesome for so many driving use cases.
Diesel engines make way less torque compared to equivalent (same era, same displacement and same boost) gasoline engines. For example, 2004 Golf V 2.0 SDI makes 140Nm while 2.0 FSI makes 200Nm Or 1994 Merc C 2.0 D makes 140Nm while 2.0 G makes 190Nm This is the reason that NA diesel engines have disappeared and turbo is a must. The only common "torque advantage" of the diesel is the lower rpm range. Also longer stroke for same displacement does not increase torque because greater leverage compansates greater force for the same pressure Actually the only true advantage diesel engines have, is efficiency. Any car maker can produce a gasoline engine cheaper, more reliable and with a better torque curve over the entire rpm range from the same displacement, than any given diesel engine. but can't even get close to the diesel efficiency. As simple as that.
I agree Diesel engines are good for efficiency, I also think diesel is good for longevity, but with all the emissions killing and cooking Diesel engines it's not worth having one anymore,plus the price of a Diesel engine upgrade ,,, and the manufacturers got people tricked into thinking 300k is a lot of miles for a diesel , so many post on you tube people bragging of 150k & 200k on their new model Diese truck
It's all about that turbo. Compare a high boost gas motor to a turbo diesel (also high boost) and you may get more torque out of the diesel you will get more horsepower out of the gas. Then just multiply the torque of the gas motor with gearing if you need that torque. It never will be as efficient because as you pointed out there is more energy in every gallon of diesel.
There are now exhaust cleaning systems for diesel engines. They no longer produce the carbon emissions as before as on the older engines or systems. A lean burning diesel engine is clean though. The issue is a rich burning diesel and is when you see the black smoke coming out of the stack or exhaust pipe. Fuel system controls are much more advanced these days which controls the heavy foot drivers. A good driver uses a light foot and the gears to move the truck etc. A bad driver always over presses the pedal. A good fuel injection control system can prevent this scenario and the exhaust cleaning system helps out as well. Cant beat a diesel for a truck.
This doesn't seem to jive with the labeling of a spark-ignition Otto cycle as a constant volume expansion where cylinder pressure drops during power stroke versus Diesel cycle labeled as a constant pressure expansion. Constant pressure suggests combustion is occurring and fuel is being supplied during a significant portion of the power (expansion) stroke. This in turn suggests slow burning in Diesel and a controlled explosion in Otto. Please elaborate?
The post contradicts ur nomenclature. This post states that diesels complete combustion sooner than the gas version. What further elaboration is needed?
The explantation regarding the false logic provided. Diesel does not complete combustion sooner, look at basic thermodynamic p-v plots of otto and diesel cycles.
Reiterating a statement from a posted vid is not an explanation and has nothing to do with logic. false logic... lol Have fun getting him to look at ur basic or non basic thermodynamic p-v plots, thats outside my purview.
I was simply referring to the false logic provided in the video. There is no problem if this is outside your scope of understanding, but I find it unfair for you to criticize his request for an elaboration. His question was valid, and you told him to rewatch the video.
Mainly because diesel is a much higher octane fuel, much higher cylinder pressure can be achieved. this works good at a relatively lower rpm but the extremely heavy rotating assembly limits rpm capability which is where the gas engine can smoke the diesel if built right, i live in a world with very few limitations as far as engines go.
Allah, where were you when Mazda broke the news of their new Skyactiv-X engine? The SPCCI engine compression combusts gasoline to gain the fuel economy and high torque of diesel without the NOx of diesel.
Jay _ I think you missed my question, I meant why gasoline engine need all the trickery new tech in order to do what diesel engine had always been doing, because principally direct injection gasoline engine is already the same design as diesel engine, but why gasoline engines still cannot do what diesel does with the same technology
Because it's a lot harder. Gasoline needs a perfect air to fuel ratio to burn the way you want. A diesel only needs to modulate the fuel to run - they don't need throttle butterfly valves.
I appreciate the nature of the video is informative and indeed it does a good job at pointing out a few peculiar aspects of diesel vs petrol engine. Unfortunately though, as far as the torque issue is concerned, this video is at best inaccurate and I'd say it misses the point completely! Turbo diesel engines have high specific torque because they are turbocharged, but they don't have any torque advantage over turbocharged petrol engines at the same level of boost. Check for instance the VW Golf R vs GTD: both 2 litre turbocharged, both 280 ft-lb @1800 rpm, no torque advantage for the diesel! Furthermore, if you go a few years back and check the specif torque figure of the rare naturally aspirated (Mercedes had them in their range back in the nineties) you see again the they are comparable to petrol units. So the question then becomes why are diesel engines ubiquitously turbocharged and with high boost levels. Because that's is the only way they can achieve high specific power, since they cannot rev as high as petrol. And here is where the explanation brought forward in the video is wrong: heavy oil doesn't burn instantly, it is actually the fact that it cannot burn fast enough that limits how high the engine can rev. Even Le Mans winning diesels didn't rev more than 5000rpm while we know that petrol units used to exceed 20k rpm in F1 and approach 10k on production cars. Energy density, compression ratio and bore/stroke do play a role but is absolutely secondary to the level of boost and not necessarily in favour of diesel. For instance, the video fails to point out that at the same displacement and combustion pressure you do get a more favorable lever arm because the crank is longer but also you loose force on the piston because it has less surface area!
But what is the Golf GTD torque at 1,000 rpm to 1,800 rpm. The designed peak torque of that diesel engine might have more to do with not wanting to overpower the transmission or other driveline components it's mated to. As I'm sure you probably know it would be easy to double the power of that GTD engine with tuning alone.
Why do older muscle car engines make more torque than horsepower? I asked my friend who owns a body shop and she says its because car manufacturers don't know what they're doing anymore. What is your take? EX: Could you explain the science behind an old Chevelle making 450hp and 500lb/ft of torque but modern Camaros only make ~460hp and 400lb/ft of torque.
Please do a Myth Busters like video on Diesel vs Gasoline emissions. My belief from what I researched but have not ever tested or proven to myself is that Diesel is actually more environmentally friendly than Gasoline. However people perceive the black smoke from a Diesel to be worse (as I believe based purely on my own very limited research) for the environment than a Gasoline engine actually is. It does make sense we hardly see Gasoline engine emissions unless its winter, yet Diesels can blow out clouds of black smoke like there is no tomorrow. So visually it does appear that a Diesel is quiet inefficient and pollutes alot more than a Gasoline engine. But higher compression is also more efficient is it not? You know alot more than I or atleast have more resources to learn and understand it then translate that to us.
Well, this encapsulates the problem with the internet. You can put out a video that is woefully misinformed, and people can't discriminate. First- Rudolph Diesel was trying to make an engine where heat is added (fuel burned) at constant temperature, as opposed to the constant volume of the Otto cycle. This proved impractical so he settled for constant pressure. To achieve this, fuel is injected slowly after TDC- hence the slow speed of diesels. Gasoline (Otto) engines burn the fuel much faster, not slower. There is no difference in the speed of burning of the fuel itself- it's how fast its injected. For the same compression ratio, the Otto cycle is actually more efficient, has higher BMEP and so produces more torque. A diesel produces more torque in practice because it has a higher compression ratio (since there is no risk of detonation- and they are usually turbocharged for this reason), hence higher BMEP. Second, bore/stroke ratio has NO influence on torque. Torque is BMEP x displacement, that's it. Please stop perpetuating this myth. I usually enjoy your videos, but I think you should post a "correction" to this one!
Very true. The Bosch PD injectors produced 2,050 bar 28,700 psi at the injectors, Since these cannot meet Euro,6 emission standards, Bosch have developed a new common rail pump that produces 2,200 bar, 30,800 psi.
Another reason Diesels make more torque is in a gasoline engine, once the spark plug fires and the fuel is burning, there is no longer any control over burn rate. The fuel burns rapidly resulting in a constant mass of gasses after the fuel burns. This implies the engine has to be designed to efficiently harness this mass of gasses whose pressure drops as the power stroke progresses. This results in a limited time that the power stroke can happen without wasted energy. A diesel, on the other hand, can control the burn rate because fuel continues to be injected during the power stroke. This results in essentially no lower limit to diesel RPM. It allows a constant pressure during the power stroke because the mass of gas in the cylinder is increasing. It also allows far longer strokes and larger bores, especially in large marine engines that develop maximum torque at maybe a 100 RPM red line.
Nice video Jason, but please don't perpetuate the ridiculous myth that longer stoke engines give more torque. The stroke length for a given capacity of engine has no effect whatsoever on torque. NONE! If you increase the stroke, you must decrease the bore to retain the same capacity, and the mechanical advantage is cancelled out exactly by the decrease in the bore, and hence the pressure on the piston. You can prove it geometrically, and algebraically. As a university educated mechanical engineer, you must be on top of such things!! Regards.
I’m sorry to say he did not explain it. He was also wrong regarding literally almost every reason he gave. There is one reason: Diesel engines don’t have to worry about knock and or pre-ignition at low engine speed like gasoline engines do. You know how on modern turbo gas engines how the middle part of the torque chart is flat? That’s a limitation to avoid knock. High pressure, high temperature, and ample time mean that the combustion would not proceed as desired if the boost pressure wasn’t reigned in. Yes, I posted this in replies. I believe it is important people see this.
Jason, stroke does not have a direct impact on Torque. Toque is a function of mean effictive pressure and displacement. For the the same displacment, the longer stoke engine would have a longer moment arm but the area will be lower, thus resulting in a lower force acting on the piston for the same efftive pressure.
That may be true of normally aspirated engines burning the same fuel at the same compression ratio. You act like a longer stroke engine necessarily will have a corresponding smaller bore and vice versa. Forget displacement because it doesn't mean the same thing when you compare a diesel engine to a gasoline engine. A short stroke gasoline engine might make the same peak torque as a long stroker of the same swept volume but it will make it at a much higher RPM which isn't conducive to getting a load rolling from a stop or for engine longevity. The diesel is not going to have the same pressure as a gasser, it will have more because the fuel is more energy dense and it's operating at a higher compression ratio, another reason the diesel engine has to be built stronger. GM tried to convert a gas engine to diesel and it was a total failure because it wasn't strong enough to handle the higher pressure and torque created by burning diesel. All that being said I think what he really means is the longer stroke does mean more leverage turning the crank at lower RPM which is the definition of a 'torquey' engine.
I do not agree and so does the manufactures specifications back me up, do not compare a turbo diesel to a normally aspirated gasoline engine. Normally aspirated diesel engines definitely makes far less torque than the equivalent gasoline engines, check the specifications yourself.
I would say just 1: the turbo, no? Don't get all this talk about such an unsexy fuel, Jeez. Without the turbo, diesels be like turtles, not the ninja kind. Haven't watched so maybe there's an example but If same displacement and same kinda turbo the diesel one would have significantly more torque?
@@Schtamper Diesels are fine without a turbo. It's just that there isn't much reason to abandon the extra power it provides. Diesels aren't turbocharged because they need it, they're turbocharged so that smaller diesels can be made to pull heavy loads and such. It's purely a cost advantage implement.
@@lewis72 nah, I'm not gonna agree with you,just simple because,the n/a diesel and petrol engine with same displacement gets the same or petrol gets even more torque,turbo is such a big thing in diesel engines,because diesels have much more boost ,newer diesels goes up to 40psi of boost,that is actually a lot. Petrol engines don't need that much boost, sometimes they don't even need a turbo,let's say if he had same displacement engines with same boost,they would have the same torque,-5% +5%,but power,I mean hp would me much higher in petrol engines. That is my explanation for this things. I wish you all a beautiful day guys :))
Isn't the combustion faster in a gasoline engine, considering that the mixture is already mixed and ready to burn when the spark happens, rather than the diesel engine, where time is needed to inject the fuel and let it mix with air? Maybe the "slow" injection is another reason why diesel can't rev too much.
A question that keeps popping up is why don't any gasoline engines use compression ignition and higher compression ratios to be more like diesel engines. Well, Mazda is doing just that with their SkyActiv-X engine, and I've covered exactly how it works: ua-cam.com/video/yNSxow3W7ek/v-deo.html
Hope everyone's having a great day, thanks for watching!
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Does that mean the new Mazda engines will have torque closer to that of a diesel?
Here may be a good question for a video: could you explain the differences/benefits between a V8 diesel and an I6, and how those engineering differences impact performance?
@Engineering Explained, You said that complete combustion of Diesel occurs sooner. But the longer carbon chain of diesel needs more time to burn than petrol which has a shorter length. I have some questions regarding this. Can you kindly spare some time in answering them please?
Mazda SkyActiv-X claims 20% more torque and horsepower while achieving 10% better fuel mileage, ive heard 10mpg improvment on all models.
It would be interesting to plot the torque over the entire 4-stroke cycle and show how this instaneous torque waveform (positive and negative) gets averaged-out by the rotational moment of inertia of the flywheel and combination of instantaneous torques from all the other cylinders.
Hey Jason. Im a wiever from lithuania. My girlfriend calls you the torque guy because she hears you say that alot. Love your videos.
Love it, thanks for watching!
All the best,
The torque guy
Where tf is lithuania
God Slave it's the place where lithium comes from ;)
Its a baltic state. Just above poland
lol u swapped the w and the v
I hear all the time that under-square engines (stroke greater than bore) produce more torque because of more leverage at crankshaft. However, a bigger bore would would result in the piston exerting more force. According to Pascal's law force is pressure times area.
Greater bore would also mean less pressure
With the advance of the EV with many having range extenders (generators only turning an electric generator), it would be nice to see what the ideal configuration for a constant speed or stepped speed generator engine. These engines will be the norm and not too far into the future.
Hey man, congrats on your great show, really enjoy learning from it. I was wondering if you could do a vid explaining what are rpms, and the fuction they do on ones vehicle. Would really appreciate if you did this, man. Thanks!
Another thing I didn't see mentioned was the fact that you can throw almost as much turbo as you want with a diesel because you're using compression ignition to ignite the diesel. You squirt the fuel in when you want ignition to occur (this is diesels "timing)", and can adjust the timing. In a gas engine obviously you cannot keep raising boost because you will get preignition. Weak links because headgaskets and studs...maybe EGT and Pyro turbo temps.
Stroke has a very significant affect on torque. If you take a rifle with a 28" barrel length firing a 7.62 NATO round and a single shot pistol with a 10" barrel firing the same round, you will have higher velocity from the 28" barrel. This has been explained as being due to the bullet spending more time with the power from the explosion being transferred to the bullet. The velocity and corresponding muzzle energy is far greater in the rifle, even though they are both using the same amount of powder.
Another great video! Maybe you could make a video going into further detail on why diesel engines do not necessarily require a throttle body and why the newer diesel engines do have them but for what purpose?
Great channel, thanks!
Thanks for watching!
I like your explanations. This one got confusing going from the diagrams in #2 to the ones in #3 because you switched the order. #2 shows gas then diesel, #3 shows diesel then gas.
3:33 i expected to see these numbers a little closer to equal. 3 x 50mm x 50mm x 80mm (volume of a cylinder) = 600,000 for the gas, 3 x 40mm x 40mm x 120mm = 576,000 but changing the 120mm stroke to 125mm makes these two engines equal instead of just close. 3 x 40mm x 40mm x 125mm = 600,000. i dont know why i paused it to double check. just food for thought.
Nice. You must be right, but here is some things that makes the difference. I think that only thing that really makes the significant difference between gas and diesel engines torque is turbo. Turbo or other charger. If you compare gas and diesel engines whitout any chargers, usually the gasoline engine makes more torque at the same volume. And if compares gas and diesel engines whit chargers, there must be charger on gasoline engine too and same boost. energy capacity of fuel does not make any difference to power. It make's difference to fueleconomy. Because it is no problem to inject more fuel to engine. problem is to get enaugh air to the engine. If compared methanol and diesel, it is possible to make more power from the methanol, even if there is much less energy at some volume.
Admiring Explanation
It seems like diesel ignite the whole mixture at a small volume so why diesel cycle’s heat addition is at constant pressure
Is it true for same displacement engine? Same power engine ?
Does petrol engine have more power for same displacement ?
Well actually main disadvantage of diesel engine is that it cannot reach gasoline engine's rpm. If we want to compare gasoline vs diesel, we should always consider turbocharger. If we think of gasoline turbocharged engine, does it lose at torque? Power to diesel????
I agree with power density, lean burn and so on : they are the reasons why diesel engines are more efficient. But it doesn't means that diesel engines have more torque AT ALL.
Diesels never USED to have more toque than an equally sized petrol engine. At least not until turbocharging and intercooling became the norm.
I remember when you could buy naturally aspirated diesels back in the 80s and 90s and they had no torque to speak of, they just gave what little they had at a very low RPM, making them very economical on fuel. I'd wager that a gasoline engine, when boosted to the same degree as a contemporary turbo diesel of the same size, will actually put out about the same torque and considerably more horsepower, thanks to its ability to rev higher. Take for example, the VW Golf GTD and Golf R. Both 2.0 engines, Both are turbocharged and intercooled. Both have around 280lb/ft of torque from around 1800rpm. But GTD has 184hp, at 4000rpm, R has 296hp at 5600rpm.
Which engine lasts longer?
Steam engines- "Hold my beer."
loke yeah they make 25hp but can go to speeds of up to 200mph
Steam tractors:
Horsepower: 150
Cylinders: 1
Torque: Enough to move the world
Also external combustion, not internal
@@renz1013 no steam engine that makes 25 is going to make anything go 200mph
@@chaztitan6457 No Steam Engine ever went significantly beyond 200 km/h (125 MPH), and these had about 2500 kW (3400 HP)
This channel taught me more that all of my years in school and college, thanks legend❤️
Some people are natural teachers and love to impart their knowledge. Too bad in most countries teachers salaries are so bad, otherwise more people with the actual calling and ability would take a teaching job
@@svarthofde2492 it's not only salary, many of them can't do what they would want to because education is very strict and systematical, they're getting fired and getting harassment in their address, basically a dead system that still exists, ignorant parents who only care about their children graduation and grades and not their knowledge doesn't help either
That doesn't reflect well on you, I must say 🤣
Maybe you were not curious or inquisitive and just expected to be spoon fed everything.
You either got a bad school or didn't studied enough.
Your post is a standard text in many yt channels...didnt school teach you to be original ?
A couple of things...if I remember my reading correctly, you have #2 backwards. It's gasoline that ignites (and burns out) almost immediately, the moment the spark plug fires. In a diesel however, fuel keeps getting injected until 20-30 degrees past Top Dead Center (TDC) on the power stroke, maintaining pressure for much longer. The reason this is important, is that when a piston is all the way up (at TDC) it produces little to no torque, the crank pointing straight up and being virtually in-line with the connecting rod. It's only when the crank has turned that the connecting rod can push against its side, creating torque. By that time, pressure in a gasoline engine has already dropped considerably, which is why you really have to hit the gas to tow anything with a gas-powered truck.
As for turbos, gas engines have their boost limited by the octane level of the fuel. As a gas engine compresses both gasoline vapors and air, too high a boost will result in detonation upon compression. In a diesel you're just compressing air, the fuel isn't injected until compression is complete. So, the only limit on turbo boost in a diesel is the strength of the engine itself--which is WHY they're built so strong.
Thanks for the comment. I don't have enough background to fully understand the first paragraph (sort of half get it) but the point about diesel turbos is clear even to me.
You do have a point.
I thought about this crank angle thing (because other people mentioned it too) for a while and I think a lot of people missunderstand how pressure works. If all the fuel is combusted immediately higher initial pressure will be created in the chamber. If the fuel is combusted slower then the chamber will start with a lower initial pressure but decrease slower because some of the fuel will be burning and counteracting that pressure loss. If as you say it would be best for the fuel to burn at the best crank-lever angle then gasolines engines would fire the spark plug then, which they dont do, most even advance the timing of the ignition before TDC.
Gasoline has a flame front, a spark plug initiates the flame which travels.
The diesel burns everywhere at once because there’s no one single point where it has to start.
I saw a diesel drag pickup running 140 lbs of boost. 140!
I'm studying thermodynamics in college, first I watched an old video about the difference between gasoline and diesel engines, and somehow I ended up watching a tons of your vids. So interesting, love the way you explain everything!
I’m doin me a good ol learn
that'll learn ya
Diesel engines are great, it’s a shame they’re being killed off.😢
Yeah, the petrol companies love inefficient engines. They require you to visit the pump more often.
@@Kit_Bear What a poor attempt to label oil companies as the problem. Environmentalists are the ones pushing against anything that burns hydrocarbon fuels.
Electric cars are the future, almost present, but believe me there will be Diesel on the road.
@@haliax8149 I'm an enviromentalist and I love diesel :-). There aren't and won't be in the near future a combustion machine more efficient and reliable than diesel.
@@haliax8149 So you are a polluter-friendly turd!
Hands down the best UA-cam channel for so many reasons.
Jason could probs do the maths to prove it.
Jason, great video. But I have a different take. Diesel fuel is an "oil" and burns SLOWER than gas. This is why diesels cannot create much horsepower; beyond about 4000 rpm the diesel piston is literally "running away from" the expansion of a slower combustion rate. But because diesel burns SLOWER, combustion reaches peak expansion LATER -- when the piston is LOWER in the cylinder. In your video on "torque vs. horsepower" you do a good job of explaining that Torque = Force X Lever Length. At Top Dead Center and Bottom Dead Center the effective "lever length" of the engine crank is ZERO. So during combustion, lever length (torque potential) starts at zero, rises to maximum as the crank turns and the lever length increases, then falls back to zero. In a "standard" gas engine (normally aspirated, square bore, decent compression ratio) peak combustion pressure is reached at ONLY 15 DEGREES OF CRANK ROTATION (midway between 1 and 2 o'clock, on a clock.) This is because gas burns quickly. But at 15 degrees "lever length" is VERY short. Torque is minimal even though combustion pressure is highest at this point. As the piston descends cylinder pressure DECREASES (because volume INCREASES.) That "typical" gas engine has its best "mechanical" torque potential at 72 degrees of crank rotation (which added to 18 degrees of conrod angle = 90 degrees. Best torque is created by pushing on the lever at 90 degrees.) But that "standard" gas engine develops peak torque at ONLY 42 DEGREES of crank rotation, because this is the best intersection of rising mechanical (torque) advantage and decreasing combustion pressure. After 42 degrees, combustion pressure drops so rapidly there's too little pressure to take advantage of the better mechanical advantage that exists at 72 degrees (the "longer lever" moment.) But because diesel burns slower, it reaches peak combustion pressure when the piston is at a LOWER point in the cylinder, where there is a greater mechanical (torque) advantage. So, diesels create higher torque, but produce very little horsepower because diesel burns too slow to keep pushing the piston faster and faster. (And this is why the torque/horsepower curves of a diesel engine "cross" at much lower rpm than gas engines.) Gasoline burns so much faster, it can "push" an engine to higher rpm, and since (as in your "torque/horsepower" video) power is the SPEED at which work is accomplished, gas engines develop higher horsepower. But less torque because they create peak combustion pressure at a less advantageous (earlier) crank angle than diesels. However, since gas engines can rev faster, they can generate more of these "peak moments" per revolution of the vehicle's wheel. So they accelerate faster, have a wider useful rpm band, and don't need as many gears to move a vehicle to a high top speed. Incidentally, the difference in "burn speed" between gas and diesel sheds light on why a super/turbocharged engine develops more power. Not only does it raise the temperature (higher thermal energy) it raises the compression ratio. Higher compression ratios cause the burn to take LONGER to complete. Meaning there is higher combustion pressure when the piston is lower in the cylinder, where there is more mechanical (torque) advantage. This is a big part of the reason why super/turbocharging either a diesel or gas engine increases its power. Sorry for the long comment. Hope this is useful...
Impressive and understandable explanation!👏👏👏👍🍻
I'm on board with this, the diesel is getting much of it's torque from the stroke length and good for you for pointing out that with the slower burn that there is most certainly a HP limit. Just another note diesels were not always turbocharged. Although sure your getting some torque increase from turbo charging diesels they really put turbo's on to get the HP up there, e.g spin them faster. A current CAT bulldozer is still turbo because why not take the extra torque but they were looking for the HP as that means you push more dirt around in a given time. Same for hauling freight on the highway, increase the HP and you can pull the load faster and get paid more. If you drive a diesel often, you will notice they mostly never "lug". They always have extra torque on hand.
I agreed with everything in your comment right up to the point where you said that higher compression slows the burn rate. I'm sure that is not true. In fact, in a gasoline (or any spark fired fuel) engine it increases the speed of the burn. This is why higher compression is necessary for extremely high rpm engines. With lower compression the burn rate hits its max at a lower rpm and will not push the piston faster. To make an engine that will run at 8000 rpm you must increase both air flow AND compression.
With diesel, turbocharging increases cylinder pressure, increases the amount of oxygen in the cylinder, and allows the injection of a lot more fuel. It's the additional fuel that creates more torque.
I agree that higher pressure when the piston is lower in the cylinder is giving the high compression engine more power. But the piston must be moving a lot faster too for this to work.
@@michaelcooley8275 You're totally correct, higher compression doesn't slow the burn rate. A volatile gas expands FURTHER when it explodes if it has been compressed more before combustion. So it takes longer to reach full expansion which means there is more combustion force when piston is lower in the cylinder, where the torque from a superior crank angle is better. If I said the burn rate is slower I spoke incorrectly. Good catch.
That's def also part of it. Its several different things put together really
Jason, love your videos and I really appreciate your ability to convey complex topics in a way that mere mortals can understand.
One of the few channels ran by a youth who's able to properly explain the automotive world in detail! I'm a mechanical engineer too and this is how these kind of topics should be explained!
Too easy to test drive expensive cars only because you have a lot of money and saying things that everyone would be able to notice only by reading a brochure.
As always can't wait for the next video! Thanks Jason \m/
Perfectly put 👍
P
Channel ran by a 'youth'....a few weeks ago, this guy said he was born in 1953...so he's 65, certainly surprised me...!
he's from 1963
Very informative vid. Thanks again for another great vid. These are great! 👍🏼
Also, diggin’ the new adding of animation..score! 😁
This was a very satisfying video sir, u never stop making one of the best auto explanation videos ever. Keep it up ur awesome work.👊🏼👊🏼
Very nice video. The way you explain things is just amazing. I am 19 year old kid who is about to join college. And I am incredibly passionate about cars and engines thats why I watch your videos.....
That can't be true! The media says the younger generation only cares about cell phones and public busses! :)
volvo09 I DON'T KNOW WHICH SURVEY YOU ARE TALKING ABOUT BUT WHAT I KNOW IS I LOVE ONLY CARS!!
volvo09 he his watching this in a phone ahahahah
passion is always the best teacher. Just go for it if you like it.
Liucu Liu cannot agree more!
Great video as usual! I would argue that in a Diesel engine complete combustion does not always occur right away.
You make it sound as if the fuel is injected in a quick shot and bam, it’s all instantly burned up just after TDC.
The duration of injection or number of separate injection events per power stroke depend on the amount of fuel needed to be injected which is primarily determined by engine load. At idle a small quick shot of fuel may be all that is needed to keep everyone happy, but obviously when pulling 40 tons over a mountain the engine will require a lot more fuel. What I was taught is that one of the beautiful things about a Diesel engine, and one of its main torque producing characteristics, is that it can continue to inject fuel and burn it throughout the entire power stroke. In convention gasoline engines a given amount of fuel and air is drawn into the cylinder in response to a given load, what’s taken in is what you get and as it burns during the power stroke the amount of downward force drops off as the fuel is used up. A diesel is capable of continuing to inject fuel throughout the stroke and will therefore maintain the downward push the whole way down, equaling more torque.
Take a look at how a normal inline injection pump meters fuel with its port and helix set up. At light load there is only a small amount of the helix exposed which means that a small amount of fuel will be injected, but the plunger will still make a full stroke, so it would still be injecting fuel during the power stroke if it had been given it. As load increases more fuel is metered in and then injected, not all at once, but throughout the power stroke.
I came here to say this.
This is called the “Cutoff Ratio” and has become electronically controlled in common rail diesels. The classic diesel thermodynamic cycle maintains constant cylinder pressure throughout the power stroke, achieved in practice by continuing to burn fuel as the piston descends and the volume increases. This means that a diesel piston is still being pushed down with the same force when its (longer) crank arm is at 90 degrees. THAT’s where the stump-pulling torque originates.
(Great channel.)
Also: common rail systems can control the rate of fuel delivery by modulating the rail pressure, so the fuel dose can be delivered quickly at high rpm and high load, or drizzled more slowly at lower load or rpm.
My CDI’s rail pressure varies from 4500psi at idle to >22,000psi at full load.
By electronically varying the timing and duration of the injection event for a given fuel dose the engine module has good control.
Fuel is injected at extremely high pressure, so it'll burn quickly and glow plugs may help
Thanks for answering a question I always wanted to ask, but could never find anyone to properly answer. That has always befuddled me about diesels, and their amazing way of producing gobs of torque.
I appreciate a lot your work: it's great, keep going!
Unfortunately I have to say something about the topic of this video:
First of all It's true that Diesel engines have higher compression ratios resulting in higher Peak firing Pressures and consequently higher values of torque BUT this is not the "true reason" why CI engines have more torque COMPARED to SI ones.
In fact, while the SI engine works always stoichiometric (or even slightly in the rich side (relative A/R (Air Fuel ratio) ~0.9)), the Diesel engine cannot work anywhere close to the stoichiometric A/R due to t bad air utilization (min relative A/R is in the order of 1.2-1.3) thus resulting in ~20% less fuel injected (in mass) for the same quantity of air in the cylinder. Lower fuel injected means lower energy released in the combustion and so lower torque (this "base" 20% deficit is partially, but non totally, compensated by the higher compression ratio and higher Diesel specific energy). If you compare the torque figures of old naturally aspirated diesels with NA SI engines of the same time you'll verify what I'm saying.
The second thing you mentioned is not wrong but it's not that relevant: the combustion of a Diesel engine is more efficient when it tends to a constant-volume combustion (like in the case of the IDEAL Otto cycle).
For partial loads, the actual duration of the two combustion processes, even if they're fundamentally different, is comparable and I would say that there are so many variables involved (speed, temperature, fuel quality, turbulence in the clinder, etc) that is difficult to say which combustion process is the most efficient.
However, at high loads, the combustion process of a SI engine is definetly occurring faster than a CI one since the latter has to fight against a "mixing controlled combustion" during which fuels struggles to find air to react with. (In fact, CI engines rotate slower than SI ones)
For what concerns the third point you presented... it's just a false myth: the higher lever of a longer stroke is counteracted by the lower force resulting from a smaller bore. If you take the condensed formula to compute engine power you'll notice that bore and stroke are multyplied together giving as a result the displacement (longer stroke -> smaller bore).
So, the reason why diesel engines have much higher specific torque than SI ones is turbocharging.
Thanks to the very high allowed boost ratio it is possible to force a lot of air inside the cylinder and so it is possible to burn more diesel than gasoline (for a given displacement). This results in a much higher torque together with a more efficient engine. (Power output, unfortunately, si affected by the "slow" combustion process that doesn't allow the engine to rotate as fast as a SI engines).
This comment doesn't want to be against you.
You've always done a great job. It's just to make things a little bit clearer.
Appreciate the feedback, thanks for sharing your insight!
Diesels also have much stronger internals resulting in more spinning mass within the engine which helps with torque. If you lighten the internals in a gasoline engine, you'll gain power but at the sacrifice of torque.
Jason I'm your fan but that was not the best movie you did. Federico pointed out why in very good and informative post above. Remeber your movies are also wached (with pleasure!) by professionals. :-)
I'm curious about one of your last statements.
"Power output, unfortunately, is affected by the "slow" combustion process that doesn't allow the engine to rotate as fast as a SI engines)."
My question is, doesn't the combustion process happens quicker on a Ci engine than in a SI engine?
As was explained in the video, (or how i think it was, and how i have interpreted) the burning process of a diesel engine happens in slightly faster instant than petrol.
And another question, when comparing both CI and SI as turbocharged engines, is it expected to the SI engine have more torque (and?) horsepower?
Thank you in advance if you answer! :)
In SI engine fuel is injected during intake stroke. It has time during intake stroke and then majority of compression stroke to vaporate and form proper A/F mixture. There is no such a time in diesel. In diesel fuel burns once its injected but injection itself takes some time thus crank angle rotation. Moreover at high loads mixture is too reach right at the injector nozzles and it needs some time to mix with air to burn. Thats why you see black smoke in diesels under load. They don't fully burn fuel. All in all diesel combustion takes longer then gas at high loads.
I don't know if you've mentioned this in other videos, but the implications of piston speed: A higher piston linear speed means that the peak force experienced by the connecting rod will be higher and thus the connecting rod must be stronger in order to withstand this force. (This also applies to the wrist pin, the piston itself, the crankshaft etc)
Absolutely beautifully executed. Bravo! Definitely liked. Already subscribed ;)
Please make a video of gasoline versus ethanol. How does a full flex fuel engine performs with each one of these fuels?
complex topic. Would be interesting but this is closer to chemistry than engineering. :) A simplified answer from me (not an expert) would be ethanol has less energy than gasoline but burns hotter and faster (cleaner) allowing for you to pump more in at a time to make up for the energy loss. High ethanol fuels can overheat an engine or burn out seals on an engine not made for it.
Unless technology has changed -- which is very probable -- it used to take 1 gallon of gasoline to produce 1 gallon of ethanol so it was more of a waste of time for anything other than performance engines like F1 or NASCAR vehicles.
acephantom903 I live in Brazil and here we have flex fuel engines for over 30 years. Nowadays more than 90% of veihcles sold each year here are flex ones. Almost every gas station here has pure ethanol (94% actually) pumps. Most flex engines here can produce more torq and power from ethanol than gasoline. In many parts here is cheaper to run on ethanol than in gasoline.
That is interesting. I wonder how you have ethanol so cheap. Maybe it isn't that the ethanol is cheap but the cost to import gasoline is high? Flex fuel engines are made to handle to increased heat while normal gasoline engines can handle a max of 20% ethanol before it gets dangerous. Because you have such high ethanol contents, your car's computer can see that and can increase fuel injection to give you stronger power than gasoline as it doesn't need as much air while combusting. Do your flex fuel vehicles also have a setting to increase fuel efficiency when running high ethanol rather than higher power? It would only be a computer setting change to have the different modes.
Fernando Sousa ... iirc...it takes 30% more ethanol to get the same energy output of gas. Ethanol also is higher octane so lots of turbo guys like it for high boost.
Fernando Sousa
I had a Brazilian classmate in tech school some 20 odd years ago, and that’s about what he said.
Gasoline is for washing parts 😂
I love seeing your videos. You do great job of explaining with great illustrations. Please keep up with your great works.
Thanks!
2nd point is wrong. Otto engines have faster combustion then diesel engines.
It's correct, these are both Otto cycle engines he's comparing.
The true reason most diesels make more BMEP is as follows:
1) They do not suffer from detonation or pre-ignition, meaning an ultimately higher Cylinder pressure and temperature is possible. (a gasoline engine would need to be run on a very high octaine fuel to produce the same BMWP without damaging abnormal combustion events)
2) Compression ratio. An engine is a thermal device, ultimate efficiency depends on compression ratio. Higher CR = more BMEP
3) Average cylinder surface area during combustion. Again, DI engines burn their fuel at lower average combustion chamber volumes and hence lose less heat to the chamber walls. More heat = more pressure = more BMEP
In all cases the charge burn angle is calibrated to position the peak pressure point at a geometrically optimum point in the stroke. For most engines (typical geometries), this is around 10 to 15 degCA ATDC. In a SI engine this is done by optimising the ignition angle (where the spark occurs) and for a DI engine by optimising the injection angle and injection mass profile.
Modern DI gasoline engines are now actually pretty close to diesel engines in terms of maximum BMEP, but can produce significantly more ultimate power as they don't suffer from the same burn rate limitation as a diesel that limits the practical speed for peak power to around 5krpm
When they used Diesel engines in LeMans racing (Audi and Peugeot) even these racing engines have the max power around 5000 Rpm.
And the reason is exactly you stated that the burn velosity restricts higher RPM.
A follow up video would be nice, since I think there is some confusion here.
I actually did some combustion development and port optimisation for the Audi R10 TDI LeMans engine, and ultimate burn rate was the power limiter that drove the engine design towards a high BMEP, low speed, low friction type architecture! Add in the mandatory air restrictor and it was always going to be a engine dominated by it's combustion efficiency rather than combustion power!
Amazing comment better than the video ! How are the new gasoline engines get torque as a diesel counterpart, but more power and they have quite good economy too ?
Well that's a amazing coincidence that i choose to mention the LeMans diesel :)
Spoken from a true garage tuner !
Awesome! I just asked my DJ to get a diesel-turntable to gain more BPM!
Hi Jason - Nice video. It would be interesting if you could do a segment (if you have not already) on how engine designers create an engine for more or less torque, along with how they control what RPM that torque reaches its peak. Obviously your video touched on some aspects of what influences torque; it would be interesting to list all the variables and their trade-offs versus each other. Thanks.
Well, there is actually only one reason that diesel engine is PERMITTED to have more torque than gas engine, and that is because diesel engine is built much tougher than a gas engine in order to handle more torque. Diesel engine has a slower combustion process therefore cannot produce torque at high speeds, so to make up for this, it must have higher torque at lower rpm to compensate for the lack of torque at higher rpm. Gas engine is designed to be light, plus risk of detonation at lower speeds with higher loads, therefore is NOT permitted to have high torque at slower speeds, because it will self-destruct. At higher rpm, gas engine cannot complete its combustion until the piston is halfway down, therefore cannot impart all of its combustion energy to the piston, so its peak torque is lower than that of the diesel engine that is ALLOWED to burn more fuel at lower speeds due to the lack of detonation risk, but that's by design only. Theoretically, a diesel and a gas engine burning the same quantity of fuel per stroke at low rpm at which complete combustion happens early in the piston downward stroke should have similar torque...but of course, in real life, the gas engine is NOT allowed to have its peak torque due to its lighter construction and the risk of detonation at lower speeds with higher loads.
I always learn a lot from you videos. Thanks for posting! I even have my wife watching some of them with me.
Happy to hear it, thank you both for watching!
Engineering Explained
Haha watching your vids is like hanging out and listening to my dad talk engineering. just you’re 40 years younger 😬
By the way I finally started watching these on my 4K tv, I can finally read the whiteboard
Diesel burns MUCH slower than gasoline, which helps it push on the piston for a longer period, taking advantage of the longer stroke... That, is why they have more torque.
It does burn slower, but that doesn't translate into producing more torque.
Let me know if you would like a more detailed explanation.
Brady Black I'm not the original commenter but I'd like a detailed explanation
Of course! To put in layman's terms, when you combust fuel past top dead center you are effectively reducing the amount of possible work you can get out of it. Fuel that has been burned at the beginning of the the power stroke will have more of its energy extracted out as work (torque). This is mildly similar to how a higher compression ratio will result in more power output. Injecting fuel late (and therefore igniting late because we are talking about a diesel engine) is reducing the amount of work the fuel could have done. Obviously this is inevitable because diesel engines can't inject fuel instantaneously, but it is in no way beneficial.
Does that make sense?
Brady Black Makes perfect sense. If you ignite the fuel when the fuel is compressed to as small space as possible (TDC) it gives more powerful expansion compared to igniting later when it would produce less force
Kinda. So the pressure IS higher (I think thats what you mean by a more powerful expansion), but it is also that the force exerted on the piston is being over more time (more crank angle degrees).
so why are no supercars diesel?
cuz torquie supercars are no fun when they are 500hp vs the fancy neighbours 707hp gasoline car, so no bragging rights wich makes them some what useless
jokes aside its as simple as that theres no braggin rights for the PR people to work with in a supercar/muscle so their job becomes a nightmare and people dont seem to care about diesel, let alone all that people that think diesel is the nastiest stuff in the world
I think it has to do with the lower rpms associated with the longer stroke length and heavier components. They have more torque but can't rev as high so in the top end gasoline ends up with more power. (I think, I could totally be wrong.)
No, you're correct. Diesels simply don't generate as much power as gasoline counterparts.
diesel has lower HP than gasoline in same displacement. for comparison, the 2.5L turbo diesel produce 180 HP while 2.5L turbocharged gasoline engine can reach 270 HP. I heard that furthest speed that diesel car can reach is 177 mph, while gasoline now is 278 mph.
ford's Focus RS has a 2.4L turbo 4-cyl I believe, with 350 HP :)
But gasoline engines run on the Otto cycle which has a constant volume heat addition straight line on the graph. This represents gasoline burns much faster than diesel. And diesel cycle has constant pressure heat addition.
Diesel does burn SLOWER than gasoline, that's why they can't rev that high...
NA diesel does not have more torque than a NA gasoline. The higher CR AND turbo (and multijet) gives higher torque. Turbocharge a gasoline and torque is there as well. Diesel efficience is higher due to higher CR (higher thermal efficienty) and higher BTU/volume compared to gasoline.
You are aware that you are contradicting everything he says in this video? Diesels can't rev that high due to longer strokes and higher piston speeds relative to rpm and diesel fuel burns quicker in an engine, almost instantaneous as it uses the heat created under much higher compression. @@ivojanssens221
@@Leemur2335 no way! Diesel engine sounds like the chain of many explosions but gasoline one doesn't. Just think, why? The answer's simple - combustion at diesel engine is the fast explosion. Not the same, and gasoline combustion flows very slowly in one cycle.
Do not agree with your suggestion that diesel has a faster speed of combustion. In fact diesel fuel burns more slowly in the engine because it is being sprayed into the cylinder with the injector over a considerable portion of the piston down stroke. In fact the ideal is to produce a constant cylinder pressure as the piston descends and this is the main reason diesels have higher torque. With a gasoline engine the spark determines almost instantaneous combustion with very rapid flame progression at the top of the piston stroke and the pressure falls off rapidly with the piston descending. Clearly this will produce lower torque. Dan Hanlon.
This is true. This is also the main reason why diesel engines can't rev past a certain point. Depending on stroke length, the theoretical limit can be anywhere between 5.5 and 7000 rpm. For most engines, it is around 6000 rpm. If you exceed this limit, you will still have considerable expansion when the piston hits BDC, grenading the engine.
You dont understand basicaly physics! please compare without turbocharger > and same displacement (not compate 1.4L gasoline with 1.9 tdi with turbo) for example>
2.0FSI have bigger torque than 2.0 Sdi 16V , please dont compare gasoline engine without turbo with diesel engine with turbo...
Its ABSOLUTE TRUE > ENGINE with more air have more torque, but with same air comsume have gasoline biger torque...
Exist (BOBA racing, AME racing and more users 800HP+) turbocharged gasoline engine have with 2.0L 1000Nm and more than 1000HP and exist evo 2.6L have 2500HW...diesel with same displacement end about 450-500HP on clear diesel, yes its exist more but with NOS or methane injection but still less than 1000hp on 2.0Tdi
Dunning-Kreuger. :)
Guy basically said diesel fuel has %10-15 more energy in it and youre trying to say gasoline car has more torque in same condition is kinda funny. Diesel engine doesnt have more air inside the piston because of only turbocharge, it has more space ! Same amount of fuel, more air, more energy in fuel will result as more torque in same conditions. Jeez dude ...
Another one of my life questions answered! Keep 'em coming! I love your videos!
That was the physics.....Now lets get to the chemistry.......Diesel has more number of carbon atoms then gasoline so it produce more energy.
all the years of chemistry and its just that easy ty buddy
You must've not watched until the end...
Erm, probably the most important part would be the turbo on the side. A non turbo diesel (aka NA diesel) has very little torque compared to equal sized petrol engine. So obviously it is the turbo. Sure, a turbocharged petrol will not make as much torque as a diesel from factory, but then it has the rpm benefit. A 2.4l 6 cylinder diesel with no turbo makes less torque than an 8V 2.3l 4 cylinder.
Volvo fan? ;)
szafirowy01 yeah... B230F vs. D24 :D But I changed brands about 3 years ago... Now it is Jaaaaaaaaaag :D
Mmm, similar to what I like ;)
Nathaniel Vas try the BW 1.9 SSI. A TDI without the turbo. Otherwise direct injected. Still makes less torque.
Sooo because it's green and green means go, it can go stronger?
Take a gasoline enginge and a diesel engine same bore and stroke and same displacement and you will find out that the gas engine makes more torque.
If you mean both with the bore and stroke of the gas ones, yes. If with an arbitrary bore/stroke, no.
You can't because of octan's flash point. Over 12 Cr, gas engine starts knocking...
Look at the Nissan Patrol from the 90's. They have a 4.2L naturally aspirated diesel (TD42) and a 4.2L naturally aspirated petrol engine (TB42). The bore and stroke are identical on both, yet the petrol produces 15% more torque and 30% more power at only 200 rpm more. I realise this is a one off but it's a great comparison of engines with identical bottom ends which eliminates the bore and stroke argument.
Reason why dragster snatches 6.2 Chevy diesel engine blocks and throw on gas heads and use electronic ignition because the blocks are the same there just beefier! then supercharge it or turbocharge it and crank up the boost!
Your math is wrong. You were supposed to compare torque/fuel, not torque/engine_configuration
TB42 is a fuel monster, while TD42 consumption is decent for its performance.
Bore / Stroke doesn't affect the torque - Consider 2 engines have the same volume and pressure. One has 2times the stroke but only half the piston area. You get 2 times the distance and half the force.
No, you will get more torque because of the longer arm of the crankshaft. But you'll get less horsepower because it can't rev as high as the short stroke engine.
Bravo, at least somebody understands physics and mechanics. Most of the posts and comments on here are just wrong, and the frightening thing is that people with no technical insight blindly accept it.
Yeah, but in fact the crankshaft of a long-stroke engine acts as a reductor, producing lower speed and higher torque.
The stroke length is very important for more torque and your illustration shows it quite clearly. In order to have a longer stroke, the crankshaft has to have a larger offset to the connecting rod in order to move the longer piston stroke. That larger distance means that the piston is in effect pushing the crankshaft around using more leverage. It's like using a longer wrench to loosen a stuck bolt. The larger offset the crankshaft has is like the longer wrench.
USWaterRockets But.... If you keep the same capacity of the cylinder then longer stroke means smaller bore and piston area thus force pushing piston down. All equalizes. ZERO effect on torqe. Jason simplified it too much imho.
Sewer Razus
Correct. Longer stroke with smaller bore means lower stress of the components, provided RPM is not too high.
Since area is dimension squared, halving bore diameter means quadrupling stroke length to get the same displacement. Force on the piston is area times pressure, area is one quarter so it's quarter the force. Torque on the shaft is force times crank length, so that's quarter the force and quadruple the length. All comes back zero. And why wouldn't it? The compressed combustion products make certain amount of mechanical work by expanding to certain volume. This means this amount of mechanical work will go to the shaft, no matter the bore and stroke configuration.
Mi 28 +1, I was very surprised Jason was so confused when he spoke about it
The thing he missed is that the diesel injection and so its burn duration is longer, so the cylinder pressure is held constant as the piston descends. This means the combustion pressure is still at its maximum when the crank is swinging past the 90’ and the piston has its best leverage. A gasoline engine has lost a significant amount of pressure by the time the crank swings through 90 degrees, so the piston isn’t generating the same torque.
It doesn't matter, power in = power out. You can't bypass thermodynamics by jumping through hoops in specific order.
Раскажи ка мне приятель почему бензине нужно 5 минут чтобы прогреть салон авто, а дизелю и 15-ти малова-то будет! Что-то ты наверно напутал!
Thank you for explaining this. I've always wondered why diesel is stronger than a gas engine.
Part of diesel efficiency is its lack of a throttle body. It always fills the cylinder with air, it varies the power output by varying how much fuel is injected. If you’ve seen a truck with just a hint of black smoke under load, they are running about as powerful as they can without wasted fuel.
Its because turbocharging...Naturally aspirated diesels have much less torque and power than gasoline engine in same displacement.
Same displacement, gasoline engine more power. Equal power, diesel more torque.
Yes, more torque but only in crank, diesels have smaller usable rpm, then they have much taller gears to achieve same vehicle speed.
I’m sorry to say he did not explain it. He was also wrong regarding literally almost every reason he gave. There is one reason: Diesel engines don’t have to worry about knock and or pre-ignition at low engine speed like gasoline engines do. You know how on modern turbo gas engines how the middle part of the torque chart is flat? That’s a limitation to avoid knock. High pressure, high temperature, and ample time mean that the combustion would not proceed as desired if the boost pressure wasn’t reigned in.
I love your videos man. I’ve never fully understood the engineering behind diesel motors. This video explained a lot for me. Thanks
Diesel makes more torque mostly because of this- most diesels have turbo, most gasoline dont have.
Not really
@@J0riS Give examples plz
@@francoismorin6806 C'est vrai que maintenant les voitures diesel sont toutes équipées de turbos mais par exemple une xantia 1.9d de 94 faisait quand même 70cv pour 123Nm ce qui est pas mal du tout comme ratio
@@J0riS bien sûr que c'est pas mal mais avec un 1.9 essence on peut sortir 190ch et 190nm assez facilement par conséquent selon moi le titre de cette vidéo est faux 🙂
@@francoismorin6806 Pas faux, je pense qu'il veut plutôt dire que les diesels ont un "ratio" couple/cheveaux plus élevé en moyenne qu'une essence
That’s why Europe mostly drives on Diesel full...
Excellent video that explains things very well, but perhaps It's also worth mentioning that although diesel fuel is more energy dense, it has a slower burn rate than gasoline, which imposes a limit on the maximum rpm at which a diesel engine can continue to produce power. That comes out at only around 4000rpm, and there's nothing to be gained by designing the engine to spin faster in order to do more work because the fuel won't be able to burn fast enough to keep up with the shorter compression/ignition cycles.
Excellent video explained in such a way even I could understand it. Bravo!!!
Happy to hear it, thanks!
LOVE IT!!! Thank you for the killer, straight to the point vid with some GREAT visual aides!!
I'm sure this was not quick and easy to put together!! (well, at least not QUICK...most likely quite easy for that brain of yours my friend!!) :-)
You touched on all the right points, however, Diesel engines do not burn evenly nor completely as you stated, the combustion in a Diesel is a Heterogeneous one , when fuel is injected, the outer part of the spray burns lean while the inner does not and takes longer to combust, secondly I expected you to expound more on the importance of no throttle body in a diesel, rather than generalizing it as pumping losses, the more technically correct term would be Higher Volumetric effiency as a result of no throttle body
And who cares about heterogenous burn? That's why diesel engines are made sturdier.
254 people were not smart enough to understand the video....
I was always taught and read that diesel combustion took longer than gas. Some of the combustion occurs in the power stroke. Otto vs Diesel cycle
Doesn't take as long, but you can (if you want to make more power) continue to inject fuel during the combustion stroke with diesels. Not efficient, but you'll make more power and it will appear to burn longer (though really it's just a continuation of fuel injection).
This is what I was taught by instructors while taking diesel technology courses. The torque output has a direct correlation to fuel timing. Because of the slow burning nature of diesel fuel, during the power stroke it can be injected into the cylinder after top dead center.
That's true which is another reason it's more suitable to a long stroke low revving engine to take full advantage of it and the fact that diesel fuel has more like 30% more energy per gallon than gasoline, not 15% as he stated.
I thought that the reason is simply that diesels are turbocharged. Naturally aspirated diesels make about the same torque as spark ignition engines.
There were a couple of questions in my mind about Diesel engines, but after watching this video, everything is clear. Thank You.
Hey Jason, can you tell me if diesel = more torque + more power+ more efficiency
Then why do sports cars use gasoline?
EDIT:
ELI5 : Petrol engines rev higher, delivering reasonably constant torque combined with ascending power output over a wide range of RPM rates (typically 1500 to 6-7000rpm) whereas diesels will achieve peak torque at lower rpm and have a much narrower band of revs across which power ascends (say 1400 to ~3500 rpm).
This essentially means that a petrol vehicle will be able to accelerate (and decelerate) more in each gear before having to change. This makes a for a much more flexible driving experience as it allows one to (eg) hold one gear between two corners while a diesel might hit it's rev limit and get "bogged" down forcing a change up after the first corner and subsequent change down before the next. As each gear change effectively loses a bit of time due to the drive not being engaged it's a less "sporty".
Diesel engines are also heavier as they can't be made of lightweight alloys.
@@hoshigakip Thank you for the crisp response. Very interesting piece of knowledge..I will remember this whenever I watch WRC or F1 or MotoGP next time :D
WEIGHT. weight is arguably more important than power. weight affects acceleration just like horsepower but it also affects cornering, handling, braking, and many other areas also.
lets relate the extremes. a motorcycle for speed and a semi truck for towing. the added weight of putting a diesel in a motorcyle would be counterproductive the better fuel economy would be dwarfed by nobody wanting such a heavy machine. and using a gas engine in a semi truck wouldnt be efficient enough for such a heavy weight. sports cars are closer to motorcycles than semi trucks.
@أحمد المنصور yeah they can hold it but what about acceleration from lower revs if u want a fast acceleration you have to shift down
Diesels actually DON'T make more torque. They are better suited to forced induction, that's all. If you compare any production naturally aspirated diesel VS petrol from the same manufacturer and time period you will see that petrol engines make more torque and much more power ie. Mercedes OM606 3L diesel 136hp, 210Nm torque, M104 3L petrol 220hp, 310Nm torque
Bro plz make a video about...
Why diesel engines ar not used in
Motercycles (bikes)?
To Heavy & really not a good idea
Very well done video, my hat is off to you sir, thank you
Couldn't you just build a gasoline engine the same way diesel engines are build (Besides the higher compresion of course)?
So wouldn't it then have the same benefits the diesel engine has?
No the fuel wouldn't work
Higher compression ratio in a gas engine results in greater tendency of knocking, therefore it's avoided
one of the best youtube teacher .....lots of love from india....
Hema Kumar i wouldn't say one of the best but he surtainly is does the job ;D.
But Diesel engines don't produce more torque, not with the same charge they don't. A turbocharged diesel engine running 30PSI produces more torque than a NA gasoline engine of similar displacement, sure, but slap a turbo on that gasoline engine and then tell me something about torque.
It's also a myth that torque has anything to do with stroke. You do not find any correlation between stroke and specific torque, engines of similar displacement and very different stroke length produce the same torque. A Chevy LT1 with 3.62 inches of stroke produces 75 pound feet per liter, a Yamaha R6 with its puny 1.67 inche stroke produces almost exactly the same specific torque (actually even more in fact because of a higher compression ratio).
And this can be easily explained: while stroke increases the lever arm to produce torque at the crank, the force on that lever arm comes from the in cylinder pressure, and force exerted by a fluid over a flat surface is pressure*area and an engine with more bore has a larger area. So you see for the same displacement if you increase stroke and reduce bore you do not actually gain any torque as what you gain in lever arm you lose in the force actually being generated on the piston and sent through the con rod.
If that were true all trucking companies would switch to gasoline engines tomorrow. Gasoline is about 50% cheaper than diesel fuel and fuel is the greatest expense of running a truck.
I have a bmw m3 v8 and a Mercedes 2.1 twin turbo remapped. The Diesel as more pull lower gears more then the v8! It’s ridiculous 🤦🏻
Excellent lecture, thank you. Makes me sad that I’m giving up my 6MT TDI Golf and have decided on the gas-driven NC Miata for cruising. I’d love a way to replicate that low-torque push for an MX-5 and get real efficiency. Diesels are awesome for so many driving use cases.
I admire people who are able to explain technical things so well! Thank you!
Diesel engines make way less torque compared to equivalent (same era, same displacement and same boost) gasoline engines.
For example, 2004 Golf V 2.0 SDI makes 140Nm while 2.0 FSI makes 200Nm
Or 1994 Merc C 2.0 D makes 140Nm while 2.0 G makes 190Nm
This is the reason that NA diesel engines have disappeared and turbo is a must.
The only common "torque advantage" of the diesel is the lower rpm range.
Also longer stroke for same displacement does not increase torque because greater leverage compansates greater force for the same pressure
Actually the only true advantage diesel engines have, is efficiency.
Any car maker can produce a gasoline engine cheaper, more reliable and with a better torque curve over the entire rpm range from the same displacement, than any given diesel engine. but can't even get close to the diesel efficiency. As simple as that.
I agree Diesel engines are good for efficiency, I also think diesel is good for longevity, but with all the emissions killing and cooking Diesel engines it's not worth having one anymore,plus the price of a Diesel engine upgrade ,,, and the manufacturers got people tricked into thinking 300k is a lot of miles for a diesel , so many post on you tube people bragging of 150k & 200k on their new model Diese truck
yes but now they make more torque i like diesel for an everyday car and gas for a weekend car
poseidonsr 2.0 SDI have 75hp and 140nm and fsi 140hp 200nm... u dont need turbo for torque lol
@@antoniotod9614 my 1.6dit subaru petrol engine has 250nm torque between 1800-4800 rpm.
Your math is wrong. You were supposed to compare torque/fuel, not torque/engine_configuration
It's all about that turbo. Compare a high boost gas motor to a turbo diesel (also high boost) and you may get more torque out of the diesel you will get more horsepower out of the gas. Then just multiply the torque of the gas motor with gearing if you need that torque. It never will be as efficient because as you pointed out there is more energy in every gallon of diesel.
if diesel burns so clean, why do they have environmental issues?
There are now exhaust cleaning systems for diesel engines. They no longer produce the carbon emissions as before as on the older engines or systems. A lean burning diesel engine is clean though. The issue is a rich burning diesel and is when you see the black smoke coming out of the stack or exhaust pipe. Fuel system controls are much more advanced these days which controls the heavy foot drivers. A good driver uses a light foot and the gears to move the truck etc. A bad driver always over presses the pedal. A good fuel injection control system can prevent this scenario and the exhaust cleaning system helps out as well. Cant beat a diesel for a truck.
This doesn't seem to jive with the labeling of a spark-ignition Otto cycle as a constant volume expansion where cylinder pressure drops during power stroke versus Diesel cycle labeled as a constant pressure expansion. Constant pressure suggests combustion is occurring and fuel is being supplied during a significant portion of the power (expansion) stroke. This in turn suggests slow burning in Diesel and a controlled explosion in Otto. Please elaborate?
see above comment reply
The post contradicts ur nomenclature. This post states that diesels complete combustion sooner than the gas version. What further elaboration is needed?
The explantation regarding the false logic provided. Diesel does not complete combustion sooner, look at basic thermodynamic p-v plots of otto and diesel cycles.
Reiterating a statement from a posted vid is not an explanation and has nothing to do with logic. false logic... lol
Have fun getting him to look at ur basic or non basic thermodynamic p-v plots, thats outside my purview.
I was simply referring to the false logic provided in the video. There is no problem if this is outside your scope of understanding, but I find it unfair for you to criticize his request for an elaboration. His question was valid, and you told him to rewatch the video.
why can't gasoline engine replicate what diesel engine does with gasoline direct injection technology
Allah Turbo I believe Mazda is doing that or almost that with their new gasoline engines
Mainly because diesel is a much higher octane fuel, much higher cylinder pressure can be achieved.
this works good at a relatively lower rpm but the extremely heavy rotating assembly limits rpm capability which is where the gas engine can smoke the diesel if built right, i live in a world with very few limitations as far as engines go.
Allah, where were you when Mazda broke the news of their new Skyactiv-X engine? The SPCCI engine compression combusts gasoline to gain the fuel economy and high torque of diesel without the NOx of diesel.
Jay _ I think you missed my question, I meant why gasoline engine need all the trickery new tech in order to do what diesel engine had always been doing, because principally direct injection gasoline engine is already the same design as diesel engine, but why gasoline engines still cannot do what diesel does with the same technology
Because it's a lot harder. Gasoline needs a perfect air to fuel ratio to burn the way you want. A diesel only needs to modulate the fuel to run - they don't need throttle butterfly valves.
I appreciate the nature of the video is informative and indeed it does a good job at pointing out a few peculiar aspects of diesel vs petrol engine.
Unfortunately though, as far as the torque issue is concerned, this video is at best inaccurate and I'd say it misses the point completely!
Turbo diesel engines have high specific torque because they are turbocharged, but they don't have any torque advantage over turbocharged petrol engines at the same level of boost. Check for instance the VW Golf R vs GTD: both 2 litre turbocharged, both 280 ft-lb @1800 rpm, no torque advantage for the diesel! Furthermore, if you go a few years back and check the specif torque figure of the rare naturally aspirated (Mercedes had them in their range back in the nineties) you see again the they are comparable to petrol units.
So the question then becomes why are diesel engines ubiquitously turbocharged and with high boost levels. Because that's is the only way they can achieve high specific power, since they cannot rev as high as petrol. And here is where the explanation brought forward in the video is wrong: heavy oil doesn't burn instantly, it is actually the fact that it cannot burn fast enough that limits how high the engine can rev. Even Le Mans winning diesels didn't rev more than 5000rpm while we know that petrol units used to exceed 20k rpm in F1 and approach 10k on production cars. Energy density, compression ratio and bore/stroke do play a role but is absolutely secondary to the level of boost and not necessarily in favour of diesel. For instance, the video fails to point out that at the same displacement and combustion pressure you do get a more favorable lever arm because the crank is longer but also you loose force on the piston because it has less surface area!
But what is the Golf GTD torque at 1,000 rpm to 1,800 rpm. The designed peak torque of that diesel engine might have more to do with not wanting to overpower the transmission or other driveline components it's mated to. As I'm sure you probably know it would be easy to double the power of that GTD engine with tuning alone.
Why do older muscle car engines make more torque than horsepower?
I asked my friend who owns a body shop and she says its because car manufacturers don't know what they're doing anymore.
What is your take?
EX: Could you explain the science behind an old Chevelle making 450hp and 500lb/ft of torque but modern Camaros only make ~460hp and 400lb/ft of torque.
Dyno tech has changed since then, maybe thats why
Please do a Myth Busters like video on Diesel vs Gasoline emissions. My belief from what I researched but have not ever tested or proven to myself is that Diesel is actually more environmentally friendly than Gasoline.
However people perceive the black smoke from a Diesel to be worse (as I believe based purely on my own very limited research) for the environment than a Gasoline engine actually is.
It does make sense we hardly see Gasoline engine emissions unless its winter, yet Diesels can blow out clouds of black smoke like there is no tomorrow. So visually it does appear that a Diesel is quiet inefficient and pollutes alot more than a Gasoline engine. But higher compression is also more efficient is it not?
You know alot more than I or atleast have more resources to learn and understand it then translate that to us.
it depends on the pollutants you consider to be most harmful and there is not a consensus on that.
Turbo gasoline engines have +/- same performance ;)
Well, this encapsulates the problem with the internet. You can put out a video that is woefully misinformed, and people can't discriminate. First- Rudolph Diesel was trying to make an engine where heat is added (fuel burned) at constant temperature, as opposed to the constant volume of the Otto cycle. This proved impractical so he settled for constant pressure. To achieve this, fuel is injected slowly after TDC- hence the slow speed of diesels. Gasoline (Otto) engines burn the fuel much faster, not slower. There is no difference in the speed of burning of the fuel itself- it's how fast its injected. For the same compression ratio, the Otto cycle is actually more efficient, has higher BMEP and so produces more torque. A diesel produces more torque in practice because it has a higher compression ratio (since there is no risk of detonation- and they are usually turbocharged for this reason), hence higher BMEP. Second, bore/stroke ratio has NO influence on torque. Torque is BMEP x displacement, that's it. Please stop perpetuating this myth. I usually enjoy your videos, but I think you should post a "correction" to this one!
He stated in the video that stroke wasn't as important in producing torque as compression ratio and fuel being injected directly into cylinder.
Very true. The Bosch PD injectors produced 2,050 bar 28,700 psi at the injectors,
Since these cannot meet Euro,6 emission standards, Bosch have developed a new common rail pump that produces 2,200 bar, 30,800 psi.
This
i appreciate how simple to understand, remember & share your knowledge, thanks for being so dang smart..
Another reason Diesels make more torque is in a gasoline engine, once the spark plug fires and the fuel is burning, there is no longer any control over burn rate. The fuel burns rapidly resulting in a constant mass of gasses after the fuel burns. This implies the engine has to be designed to efficiently harness this mass of gasses whose pressure drops as the power stroke progresses. This results in a limited time that the power stroke can happen without wasted energy. A diesel, on the other hand, can control the burn rate because fuel continues to be injected during the power stroke. This results in essentially no lower limit to diesel RPM. It allows a constant pressure during the power stroke because the mass of gas in the cylinder is increasing. It also allows far longer strokes and larger bores, especially in large marine engines that develop maximum torque at maybe a 100 RPM red line.
Nice video Jason, but please don't perpetuate the ridiculous myth that longer stoke engines give more torque. The stroke length for a given capacity of engine has no effect whatsoever on torque. NONE! If you increase the stroke, you must decrease the bore to retain the same capacity, and the mechanical advantage is cancelled out exactly by the decrease in the bore, and hence the pressure on the piston. You can prove it geometrically, and algebraically. As a university educated mechanical engineer, you must be on top of such things!! Regards.
janet53589 hi Janet...thought about your comment... would you agree that torque peak will come at a lot lower rpm than short stroke big bore?
I’m sorry to say he did not explain it. He was also wrong regarding literally almost every reason he gave. There is one reason: Diesel engines don’t have to worry about knock and or pre-ignition at low engine speed like gasoline engines do. You know how on modern turbo gas engines how the middle part of the torque chart is flat? That’s a limitation to avoid knock. High pressure, high temperature, and ample time mean that the combustion would not proceed as desired if the boost pressure wasn’t reigned in. Yes, I posted this in replies. I believe it is important people see this.
He wasn't wrong about a single reason he gave.And your reason doesn't defeat any of them....
Jason, stroke does not have a direct impact on Torque. Toque is a function of mean effictive pressure and displacement. For the the same displacment, the longer stoke engine would have a longer moment arm but the area will be lower, thus resulting in a lower force acting on the piston for the same efftive pressure.
Agree totally :-)
That may be true of normally aspirated engines burning the same fuel at the same compression ratio. You act like a longer stroke engine necessarily will have a corresponding smaller bore and vice versa. Forget displacement because it doesn't mean the same thing when you compare a diesel engine to a gasoline engine. A short stroke gasoline engine might make the same peak torque as a long stroker of the same swept volume but it will make it at a much higher RPM which isn't conducive to getting a load rolling from a stop or for engine longevity. The diesel is not going to have the same pressure as a gasser, it will have more because the fuel is more energy dense and it's operating at a higher compression ratio, another reason the diesel engine has to be built stronger. GM tried to convert a gas engine to diesel and it was a total failure because it wasn't strong enough to handle the higher pressure and torque created by burning diesel.
All that being said I think what he really means is the longer stroke does mean more leverage turning the crank at lower RPM which is the definition of a 'torquey' engine.
I love my 520D ❤️
amazing car, amazing engine
What about 525D :D
Jerrypintoswe drive and 530d and get back here..
Bharath M of course its faster. Still love my 520D
Bharath M or 535d
I do not agree and so does the manufactures specifications back me up, do not compare a turbo diesel to a normally aspirated gasoline engine.
Normally aspirated diesel engines definitely makes far less torque than the equivalent gasoline engines, check the specifications yourself.
Why can’t gasoline use the self ignition
Not true. I put diesel into my car by accident one time and it made LESS torque.
1:Longer stroke
2:Heavier parts
3:bigger compress ratio.
I would say just 1: the turbo, no?
Don't get all this talk about such an unsexy fuel, Jeez. Without the turbo, diesels be like turtles, not the ninja kind.
Haven't watched so maybe there's an example but If same displacement and same kinda turbo the diesel one would have significantly more torque?
@@Schtamper Diesels are fine without a turbo. It's just that there isn't much reason to abandon the extra power it provides. Diesels aren't turbocharged because they need it, they're turbocharged so that smaller diesels can be made to pull heavy loads and such. It's purely a cost advantage implement.
@@Schtamper
Non-turboed diesels still generally have more torque than similarly-powerful petrols, even if they do have sod all power.
@@lewis72 nah, I'm not gonna agree with you,just simple because,the n/a diesel and petrol engine with same displacement gets the same or petrol gets even more torque,turbo is such a big thing in diesel engines,because diesels have much more boost ,newer diesels goes up to 40psi of boost,that is actually a lot. Petrol engines don't need that much boost, sometimes they don't even need a turbo,let's say if he had same displacement engines with same boost,they would have the same torque,-5% +5%,but power,I mean hp would me much higher in petrol engines. That is my explanation for this things.
I wish you all a beautiful day guys :))
Torque is the product of BMEP and displacement. Stroke length HAS NOTHING DO DO WITH IT. How long is this misconception going to persist ffs.
Wrong,wrong and wrong,diesel engine make more torque,because diesel fuel burn slow...bye.
Isn't the combustion faster in a gasoline engine, considering that the mixture is already mixed and ready to burn when the spark happens, rather than the diesel engine, where time is needed to inject the fuel and let it mix with air? Maybe the "slow" injection is another reason why diesel can't rev too much.
It is diesels slower burning that restricts revs.