Great explanation Jason! That makes sense! I did an egr cleaning video where I said injecting exhaust gases cools the cylinder temps and people were not understanding. I will reference them to this video now!
Just want some advice sir,, my forester 16 at 60k km is starting to show idle problem.. only at warm start, rpm drops low (almost stall) and bounces back up.. at cold start its idling normally high as cold engine then gradually drops.. the problem usually only occurs at warm, like after a long trip and engine rest for an hour,. Any advice sir,, where to look first before I bring it to mechanic.. thanks. More power
I think the running lean/hot originally came from the 2 stroke dirt bikes where the gas and oil mixture lubricated the engine. Running a super lean mix (more power) would cause the engine to seize up from lack of lubrication. In this case lean=hot from lack of lube=engine meltdown.
I think you got all this wrong. First fuel acts as a coolant itself. Then a lean mixture will behave like a burst in flame instead of a controlled expansion then could cause knocking, and not by having another hot spot in the cylinder. The lean mixture will ignite too quickly and try to stop the piston to reach TDC that causes knocking. This is why cars have knock sensors that will retard the ignition in that case. So having too lean mixture will retain the heat longer into the cylinder, make the engine work harder and will make it running more hot. Too rich mixture then will cause it to continue burning after power stroke and dissipate heat into the exhaust valve and the pipe. So there is a sweet spot to get that is called "well tuned engine".
I am viewing this video from the point of view of a general aviation pilot (in flight sims only!!!). For MOST piston aircraft the mixture is left up to the pilot. Full rich for takeoffs and landings, and since most of them are air cooled, the mixture is set to control Exhaust Gas Temp and Cylinder Head Temp. For climbing, somewhat rich, and for eco-cruise, somewhat lean of peak temp. Pull the mixture control out until just past peak EGT. The engine cruising is making less heat due to the throttle setting being reduced after climbing, so lean of peak doesn't cause overheating of the cylinder head. I think some planes have automated this, and I feel all should! The pilot already has enough to do! This needs to be adjusted constantly as the plane climbs higher. ( The higher you climb, but more you need to pull the control out.) I had my Prius Prime up to 14,??? feet at Pike's Peak, and never had to adjust anything. 15K' is the ceiling for most naturally aspirated piston aircraft, so my Prius outclimed most of them with no adjustments on my part. (Or in any car!). Of course no cars currently sold that I know of are still air cooled as most GA aircraft are. The Cessna 152 starts struggling at 5K' (in my sim, I have never flown any plane IRL). My 182 Turbo craps out at around 22K, but is way happy over 15K. Very necessary flying in Papua and Papau New Guinea, or Chile.
Thank you for this video! It looks like people in the comments that disagree are mostly not watching the whole video or are not opening their mind to the fact that there is a big difference between the technical term "lean" and the garage tuner's term "lean."
@@kevinghifari2330 I think he means the technical term lean indicates running above the stoichiometric ratio, where temperatures will be cooler than at the ratio. What a tuner means by lean is below stoichiometric, but above a ratio of 11-12, where the temperatures will still be rising the leaner you get until you get to above 14.7 (which in practice most current cars will not reach in WOT situations).
Agreed. People use "lean" as a relative measure, not by using the stoichiometric measure of ratio. In a way, they are being correct, but they aren't using a technical term.
Lean means higher combustion temps; that's why lean mixtures are responsible for creating NOx. Fuel droplets evaporate as they enter the combustion chamber, lowering charge temperature. This is one of the advantages of E85 fuel, as the lower energy density requires increased volume, which in turn lowers charge temps further. The engine running "cool" or "hot" has nothing to do with the mixture. That's a function of the cooling system. Governments, manufacturers, and chemists will all disagree with him. Fail a tail-pipe "sniffer" smog test for high NOx, the answer is always the same. Lean mixture. Either address the lean condition, or fix the EGR system designed to lower cylinder temps and drop the smog.
On some simple prop airplanes they have a mixture lever to lean or rich the fuel to air mixture, because the higher you go the less air there is/ less fuel you need. Richening the mix is also used to help cool the engine-- I was once flying on a hot day, left the fuel full rich, barely maintained max allowable temp and saved the day. The end
Pressure and Mass Fraction vs. Rotation. Otherwise known as the “sweet spot”. Ignition timing for power when lean means more advance in the ignition timing. Why? Because, leaner mixtures burn much slower. Therefore, the sweet spot just past TDC needs to have more ignition advance so, the pressure is present at the same time as it would have been. It’s the other side of the equation. If you do one thing(leaning the mixture)one must consider the other changes this creates and allow for it. In this case it’s more advance for the ignition event. David Vizard Performance has stuff on this. You guys will love it.
Actually, people say that running lean causes increasing the EGT. Because, lean combustion is slower than the rich combustion. That's why combustion speed is decreasing and combustion shifts towards to BDC. Exhaust valves are opening before BDC. Then you are exhausting the gas that just completely burned or already burning.
@@B10401 You can only advance timing so much until you run into detonation issues because you are igniting the charge while it is still getting squeezed for a while. You also loose mechanical advantage. The leverage the rod has on the crank is the lowest at TDC. TDI's exploit increasing mechanical advantage by putting in the fuel in pulses so that the fuel burning happens after TDC as well as mechanical advantage is increasing. Also engines don't run at an ideal. O2 sensor feedback is switching based. Your engine is actually running a bit lean and then a bit fat compared to the ideal over and over again as the O2/Fuel air sensor switches back and forth. You'd need a sensor on each exhaust port and individual exhausts as well as TDI to even try to run at a constant ideal mixture for the engine design. But in summation the problem is EE here is saying ideal is stoichiometric ideal. When in reality ideal is the ideal ratio for the engine design. When someone says leaned out and got too hot they aren't saying it went over 14.7 A/F they are saying it leaned out compared to the ideal design ratio which can be anywhere from 11-14 for the engine.
@@B10401 Yes, I am thinking mostly the same. If an engine is running Lean, meaning there is a greater part of air mass for each amount of fuel mass, beyond the stoichiometric ratio, the mixture should (from what I can suppose) burn faster, as it would be "easier" for each fuel molecule to bond with an O2 molecule because these are in excess. Still I do think poor mixing is the main reason why an engine may run hotter, considering not every fuel molecule can bond with its corresponding O2 molecule properly, resulting in greater fuel consumption and a reduced effective power (power produced for a specific volume of fuel burnt).
I’m only a kid interested in cars and whatever that has an engine. Sometimes your videos make mot much sense to me but I still watch it and look at your fantastic drawings. Good work Jason :)
Hey i have a fun topic. Engine power is greater with colder air. What are the rates for atmospheric and forced induction horsepower bumps summer vs winter. It would make a fun video!
Power is not, in all cases, greater with colder air. Humidity will combat the colder density. That is why density/ altitude is used to calculate actual horse power. I.E. you will make less horsepower in Colorado at 30° than in Maryland at 60°. Because of altitude and air density.
@@yinzer_412_ Think he was saying something more like Maryland at 60° vs Maryland at 30° and the effects on both N/A and forced induction. Furthermore, i would also like to see N/A vs turbo vs supercharger. Then throw in humidity to talk about molecular weight while we're at it.
65° at about 23% humidity is pretty much the perfect condition for a dyno test. Yes, air is more dense when colder but that requires more fuel. Fuel that has to be more reactive to ignite the colder air. This typically requires a lower octane. Thats why E85 guys always have somewhere between E40 and E60 in the winter time otherwise the car may misfire. In a nut shell the extra fuel needed for ignition will actually take up more volume in the combustion chamber. It has to be more reactive (lower octane) and there has to be more of it. Not good for HP because its like the car is running rich just to operate.
I think the thing he overlooked was having a lean mixture means there is more oxygen in the cylinder which produces a faster and hotter flame-front, thus, overheating. Engineers have spent over a century studying this and I tend to believe them
Only a hotter flame front if there is fuel to use with that oxygen. If there is extra oxygen then needed for perfect combustion that won't make the flame front hotter. You would just have unused oxygen.
@@Alobster1 That's not how it works. Oxygen is an accelerant- the flame absolutely burns hotter and faster when a higher concentration of oxygen is present.
Its not about oxygen, fuel acts as a cooling agent, so when ran lean, there is no extra fuel in the combustion chamber, also coolant circulates around and top of the engine, not inside the engine's combustion chamber to cool down, same for the oil, it's lubricates inside the piston rings area, so when ran rich, there is extra fuel available which takes the heat away from the engine 😀
Basis of his argument is that any mixture < 14.7 : 1 is rich People say your engine is hot because it is too lean, which does not mean > 14.7 : 1 e.g. 14:1 is too lean
TL;DR of video: "lean relative to ideal stoichiometric combustion" is different to "lean relative to ideal AFR for maximum power which can still be technically rich of 14.7:1"
I think it comes from the aviation community, running rich (of peak) and running lean (of peak). In somewhat older planes you usually have manual mixture control, and in even older planes with engines that have carburators, you could not lean the engine to much due to uneven fuel distribution in different cilinders, which could cause overheating of certain cilinderheads. In fuel injected engines, there is no uneven fuel distribution into the cilinders, so running lean of peak in fuel injected engines saves gas, carbon build-up and reduces emissions
If you extend the second graph (x axis) to show more lean ratios (>15) the temps go down again. It's called lean-of-peak (LOP) that leads to lowest emissions and best economy (for a minor power loss) used in aviation
The Fuji triple 750 2 stroke in the 1990s polaris watercraft all had a design flaw: the 3 carburetors for each cylinder were hooked up in serial from a single-output fuel pump. After one season on pump gas, an owner would park the craft for the winter, start it up the next summer, take off skiing and within 5 or so minutes break down having burned a hole in the piston on the last cylinder, due to ethanol gunk clogging the previous two carburetors and starving the 3rd for fuel. Less fuel means less cooling effect, which is what people are referring to when they say "lean runs hot". it simply means "if you lessen the fuel, you'll create a hotter cylinder" not "if you're technically lean compared to stoichiometric, you're hotter than rich compared to stoichiometric" That's a meaningless statement anyway, because who cares? Perfectly stated, would probably be, "you're running rich obviously, but if you reduce that richness in the direction of leaner, you'll move more toward ideal ratios, and increase cylinder temps, and can damage your equipment, even if you were still technically "rich". Edit: the fix for the fujis, is to buy them cheap with burned pistons, rebuild the engine, and replace the single output fuel pump with a 3 output, and plug all carb outputs.
I'm not that sure about your hard statement: Running Lean does increase temperatures, but inside engine, specially inside combustion chamber, this can put alloys and lubrication under excessive stress and strain, also, higher combustion temperatures, higher flame temperatures, increase NOx emissions, as you pointed. Many approaches have been attempted, from Water Injection in WW II Aircraft engines (see AEHS), to tactics as in SAE papers: 860533 (EGR); 741091 (Cooling liquids); 840237 (Ethanol, E10); to patents, such as Utility Models ES0220611; ES0248478. If you can't be consoled, is because you don't want to.
Jason, Another great video and spot on correct with all your facts (if we ignore the EGR acronym mistake that you corrected in production). From reading the comments below it still seems that there are many people who struggle to understand the difference between "less rich" and lean.
Little bit lean mixture results in less vaporised fuel in combustion chamber and runs a bit hotter and thus producing more NOx emissions in gassoline engines. Have been waiting for this line, but it never came. However thats what they teach you in the school and there are plenty of A/F vs NOx graphs on the internet supporting it.
Seems like a very nitpicky conclusion. Running lean increases cylinder and exhaust temperatures, which the graph on the right shows, even though the "technical" answer is that the flame itself burns cooler both lean and rich. Running lean runs to knocking which causes pitting and can damage the catalytic converter from hot exhaust gasses, so saying "running lean causes higher temperatures" is a valid thing to say.
Great video Jason. Please can you do a diesel specific version and the challenges with balancing out efficiency, NOx and soot? Is it better to accelerate a diesel in a lower gear rather than a higher gear from a soot perspective (vs fuel efficiency perspective)? Thanks!
Being able to measure peak EGT is crucial to getting this right. Running a turbocharged aircraft engine at higher rpms than book, leaner settings than book takes extra tuning but can totally change an aircraft's performance envelope.
Theory sounds great. Now please explain why in flight training we are taught AND SHOWN that we can try to conserve fuel in flight by leaning out the mixture--until the cylinder head temp gauge starts to show it is too hot. You're missing something here, the flight instructors and the gauges don't fib.
@@scottyh72 , totally wrong. When the combustion temperatures maximize, then the least amount of heat is conducted to the engine because the explosion is MUCH faster, more efficient, more powerful, and shorter duration. An ideal maximum explosion is far to fast to be able to heat up the engine much at all. It is a weak and slow combustion that conducts the maximum heat to the engine. And in fact, excess oxygen is extremely corrosive at under those conditions, and you will melt pistons and valves. The way to make the engine run coolest and last longest is by achieving the highest possible temperatures, which then are exploding so efficiently that there is no time for hardly any heat to be conducted to the engine.
@@scottyh72 90% of this is a semantics problem - Jason was using rich = richer than stoichiometric and lean = leaner than stoichiometric, but as he states, stoichiometry is not really a target for internal combustion engines. The alternate definition that causes trouble is rich = richer than best power and lean = leaner than best power
School them Lyfan. The video and title is just misleading. Needs to be more specific with the level of lean he is talking about and not just point blank lean.
@@kirkaugustin2232 He's not totally wrong he's absolutely spot on, you still misunderstand what he said, the video and how this whole temperature variation with AFR works. Air planes run rich, because a rich engine is less likely to stall. When cruising a pilot can increase air/fuel ratio to improve efficiency, and when doing so is taking the engine from rich to stoichiometric which is where temperature peaks. Air plane engines (piston ones anyway) never run lean, they run slightly rich to very rich.
I can think of at least one mechanism through which, leaning the mixture will increase the *exhaust* temperature: My understanding is that leaning out the mixture slows down combustion. The slower the heat is released into the combustion chamber, the less time there is for this heat to be extracted as a mechanical work by the piston. An extreme version of this effect is turbo antilag by ignition retardation - if you don't extract the energy, the heat stays in the gas. Now the question of how big this effect is depends on how much is combustion slowed down by a lean mixture in the real world. I don't have any numeric data on this but I remember that leaning out the idle screw on my wr450 would cause the exhaust header to glow just when idling. It would be pretty cool to see if you could cover combustion speed and how it changes with the AF ratio. Cheers and thanks for all your awesome content!
The first thing that came to mind is that you have to set engine tuning aside. Stock engine is built to run around 14:1 and it will survive. But if you have for example a 9:1 compression ratio and put like 1,5bar of boost on it, it will fail due to hot combustion. By running lean in tuning prospective is running above 13:1 which is not lean in normal cases. Edit you mentioned my point in the end.
An unloaded diesel engine is a prime example of running lean and having low combustion temperatures. As throttle is increased, ideal ratio is approached resulting in higher temperatures.
My personal experience attests to the ~12.5 or so wide-open throttle AFRs in N/A applications, and often ~11.5 in turbocharged applications we end up at. I'm very well vetted in my platform (Mazdaspeed 3), and when we tune we almost always end up ~11.5 or so on 93 and ~12.0 or so on ethanol mixes to stave off knock (in wide-open throttle regions; cruising regions we always shoot for stoichiometric). We've learned that going leaner than these can cause ring-butting and cracked ringlands due to cylinder heat. Being DI, we know that the extra fuel spray does cool combustion temps even more because it's injected directly into the combustion chamber, which is why we empirically see lower knock in the telemetry when doing so (in part). Additionally (and maybe outside of the scope of this video), ignition timing can have a dramatic effect on cylinder temps. Have you (or will you) made a video on this?
In general aviation pilots control their own mixture in the plane. We do this because as we get higher there is less air, therefore we don't need as much fuel going into the engine. I bring this up because the common way we lean the engine is to pull the mixture back (lean) and watch the EGT. When we hit peak EGT we will then push in the mixture (rich) again watching the EGT and then stop when we get 50 degrees cooler on the EGT. This is called being rich of peak. It'll generally give us our best power, and best range. But there is a thing called lean of peak. Some planes are ok being flown lean of peak, some are not. But as you can guess when we are at peak EGT we lean out a bit more, and the EGT will start going back down. Flying at peak EGT or lean of peak will give us best endurance.
I was modeling an engine trying to use boost/back pressure rather than throttle to moderate output and it kept showing that if it went lean, it actually ran cooler at the exhaust, even if it was compressing more air at a high CR. Hence, I found your video for a second opinion. Thanks!
We used to intentionally lean out our mixture in go-kart racing. Get a little more RPM but the temperature would climb. Had to turn it back after making the pass or you would overheat. Don't know if it was the RPM or the mixture that caused it to get hotter, but it did get hotter. That was running on methanol. Could just be the case that the air cooled engines couldn't handle running at peak mixture.
And that's coming from the driver that actually physically turned the mixture screw while driving and watched (and had records of) the tach and engine temps. It's not an "I heard they did this..." thing. We really did it mid race to make passes and if you forgot to turn it back out you had about 2 laps before your overtemp warnings were going off... maybe. That would happen sometimes if you didn't manage to make the pass.
Also, my dad hated this and would remove the coin I stuck in the mixture screw to adjust it every so often... lol Just jam a penny or nickel (depending on which carb you had) in there and boom, it's a finger knob.
that dates back to carburetor days...i had a 1987 xr600 that ran much cooler with bigger jets but of course an old air cooled engine with two carbs dumping gas into a giant single is nothing like anything today
If you run lean and create a knock then it will run hotter. It's the same as advancing the timing. The burnt gases will spend a longer time in the combustion chamber causing the engine to run hotter.
Anyone who flies a piston-driven propeller airplane knows this to be true -- when you set optimum cruising power, you adjust the air/fuel mixture until you see peak exhaust temp.. Make the mixture richer *or leaner* and the exhaust temps go down. There's a point -- stoichiometric -- where exhaust temps are maximum.
You can draw all the cartoon pictures you want to explain this using every bit of science you can think of. But out here in the real world.......because I've seen it many times.............a lean engine can (and usually does) actually run hotter. I just had a Ford 5.4L in my shop with a low fuel pressure issue. The codes in it were for lean running conditions for bank 1 and 2. Its also had codes P1299 and P1285 (Cylinder head temps to high). The customer also told me that the coolant temp gauge was up way higher than it usually is. We fixed the fuel issue and the high cylinder head temp codes did not come back. This is just one example of many that I've seen.
Back when I was at a place with a Dyno, we did some egr testing on my old Datsun 720. It had extensive engine modifications but we found a 7rwhp gain with lower emissions (didn't test NOx) with the EGR blocked. I miss that little truck.
It's my belief that "Lean vs. Rich" in regards to temperature is arbitrary, and subject to vernacular. In the construction equipment service industry, running "Dead Lean" refers the perfect combination of air-fuel, making for 100% ignition, and exhibiting a blue exhaust flame from the typical short systems on non-catalyst engines, such as on compressors and aerial work platforms. It also produces peak running temperatures. More specifically, this is in reference to gasoline engines running at optimal high rpm that coincide with the peak of the torque curve, and under a steady load. In my case, this would involve a prime mover turning single or stacked hydraulic pumps. From my perspective, the subject is more about semantics than it is about NOx production levels, but this is a good study of stoichometry, and a fine presentation.
Running lean may cause a slower flame travel, thus the af mix may still be burning when the exhaust valve opens. This causes a hot exhaust valve and hot exhaust headers. Im not sure, but a lean mix flame front may slowly progress away from the spark, causing the extra air to compress and heat sufficient to ignite the af mix, thus causing the second flame front diagonally from the spark plug, thus causing knock. Another possibility is that the now hot exhaust valve causes a second ignition thus causing a knock when both fronts collide.
I just realized Flight Simulator kinda models this with the cessna, as you enrich it, temp goes up then back down. I was reading online about a month ago how the highest EGT is most efficent. Thanks for the awesome video man!
Jason, some time ago I got a wideband O2 sensor onto my GX390 go kart engine, in order to tunemy needled carburator... I realized then that running a misture above 1.00 lambda (and knowing that 1.00 lambda = 14.7 air/fuel ideal ratio), the engine simply cuts, simiilarly to a ignition cut... The engine simply stops to generate power, as I said, like if I turned off it while running... That was the exactly feeling I got when lambda got higher than 1.00 on the O2 display sensor... I concluded that no engine can run with a mixture above 1.00 lambda, and so, all mixtures we can work on are less richer (closer to 1.00 lambda) or more richer (values smaller than 1.00), but all mixtures are always richer from this lambda perspective... Using this perception and what you said on your video, it makes sense to say that a lean mixture makes combustion chamber temperatures to be high... But this lean mixture is, in fact, a rich mixture closer to the 14.7 (or lambda 1.00).... Does this make sense??? And is my conclusion that no engine can run proper on O2 sensor readings above 1.00 (real lean mixture) correct??? Cheers and thanks for this excelent engineering channel!!! I really enjoy your videos!!!
Heat output is a function of amount of fuel burnt and efficiency of combustion, will create same temperature curve... alternate explanation for temperature curve explanation.
This video is pedantic. The temperature increases up to around 15:1 and then plummets. It plummets because the engine will not run correctly, therefore the statement 'lean engines do not run hot' is wrong because it does run hot' in the region where the engine actually still runs. Anyone running a lean engine that still performs will see a temperature increase. You've countered the false statement that 'a lean engine runs hot' with another false statement that is ' it does not run hot' both are wrong as they don't account for eachother, but in the practical world with engines in the performing regions of afr ratios they will run hotter.
My R1 came with a full Akropovik exhaust system but didn’t have a power commander or ECU flash. It’s like riding an oven. I’ll get a fuel controller one of these days. At least that’s what I keep telling myself.
Hey Jason, here in the UK pretty much everyone with a diesel car has it tuned, often finding about 15-20% extra power. There has to be a downside-surely! There is an real lack of science available as to what's happening in the car, plenty of stories but not much fact. How about a video talking about it? do they start pouring out NOx, start wrecking bearings etc. etc. Also if they could perform better why didn't they do it from the factory.
That is not what the exhaust valves and exhaust manifold said....... running "lean" makes your egt's hot. More fuel in exhaust = cool, less fuel in exhaust = hot. If an engines cooling system is really efficient (usually they are not), then it will keep a engine cool untill it passes it's efficiency threshold. The after effects of running lean is what makes everything hot or over heat, hotter under hood temps, hotter exhaust components, hotter cat converter, and hot oitside temps = overheated engine. Just my .02 cents worth working on cars for the last 17 years or so.....
Remapping your egr from working makes your much nicer to drive. What's the effect of running up to 10% petrol in a diesel engine according to the owners manual in very cold climates?
Nowhere do you talk about the length of TIME for a lean charge to burn. Lean does indeed make engines run hotter because the charge takes a far longer time to burn, thus bathing the engine's internal surfaces in more heat. Your graph is wrong, temperature rises considerably lean of 14.7 A/F ratio. I've seen piston's from a friend's Suzuki sport bike which had partially melted surfaces simply because he installed a sport exhaust but didn't think it was necessary to re-jet the carbs in order for the fuel to match the increased portion of air.....
So if we are able to decrease cylinder temperatures by adding more air into the combustion chamber, then why do we use EGR gas, since its main role is to reduce NOx by decreasing cylinder temperatures? I mean, by making the air/fuel ratio lean we can reduce temperatures as well.
Sorry buddy but this is wrong. Other comments deal with one of the reasons why but there is also an interaction between AFR and ignition timing which causes even further temperature rise when running at high loads. Note also that almost no gasoline engines run lean of stoichiometry when hot due to the AFR requirements of the three way catalyst. Please do a little more research on this topic and demonstrate your integrity by posting an update. Thanks
Jason, it would seem the maximum temperature would be reached on the rich side of the stoic ratio, followed by the subsequent decline. According to your description of the ideal stoic of 14.7:1 not providing real world homogenous mixture of gas and air (hot vs cold pockets in the combustion chamber) to achieve complete combustion, lowering the A/F, up to some point, allows "all" the hydrocarbons to be combusted. This should lead to an increase in chamber temperature. Now, if thereafter you reduce the A/F, you then run into excess fuel that will not be burned, and will necessarily withdraw heat from the chamber through the fuel evaporation process, as you described. Am I interpreting the scenario correctly? Thanks!
I've seized a number of engines over the years. I've always called and learned it was due to running too lean. Funny how you explained it as not rich enough causing the rise in temps. Melted 2-stroke pistons result from high temps and the not rich enough allowed me to see why. Still, I've always called it running too lean.
Older engines with no EGO sensor and no computerized ignition did run hot when lean. Lean burns slower and higher throttle takes away vacuum timing advance. Slower burn means flame, even though cooler, has more exposure to coolant given the greater capacity to pass heat into coolant through cylinder walls. The engine management systems of the last few decades would have check engine light on and would have controlled the situation and limited ill effects. Like many things, old ideas die hard.
I have experimented with a carbureted engines and only observed the highest temperatures on stoichiometric AFRs (and a bit richer). Never observed an engine running hotter on lean AFR.
My point is that this is no longer happening but it is not an unfounded urban legend. Years ago I worked in a GM dealer I’m the truck shop. C20 through C65 trucks running in the hills in my area would run hot even in cooler weather when they had the very common faulty fuel pumps with the return line that many big blocks and small blocks used. The driver would keep the pedal matted and drive a fuel starved vehicle up the hills and have gauges climb. The complaint of temp gauge going near the top would go away with a new pump and also return line restrictor and fuel pressure to carb staying at over 3 psi wide open loaded up hill.
Ante Radić no, I had a tech support and training role with a car manufacturer until a few months back. I was in that job for 30 years. My post was to address that this was not urban legend completely as older technology would overheat when lean with no other methods in play to limit the effects.
You didn’t bring it home till the last couple of minutes... As you stated, the nomenclature is based off the optimum ratio (not stoichiometric,) and thus “lean is mean” and “lean is hot” hold true.
The stokiometric ratio is the most efficient mixture of fuel and air needed to create and explosion without waste , but engines are tuned to run slightly bellow that to create a slower more controller burn that the engine components can withstand , this also prevents pre-ignition of the mixture as the engine temperature and pressure are enough to ignite a perfect mixture. So running Lean in engineering terms for an engine will definitely make it run hotter. The engine will make more power and respond better but it will fail at some point.
It is, problem is though, if you go torwards stoichiometric lean the spark plug will have trouble ignite the mixture. so you go torwards rich to keep the temperatures in check. What is often called "lean" means from rich more torwards stoichiometric.
Okay that makes sense, I was disagreeing at the beginning although the science makes sense.. In the end it's about technicality.. you can say "running lean-ER than stock will make your engine over heat" and that's true.. and that's what most people mean I guess.. but thanks for clearing it up
Correct. Had a lot of people asking about my videos on NOx emissions reduced by running lean, and running cooler, saying they thought lean meant hotter, hence this video. :)
Wow............just wow, amazing video friend, ...I was having tuning problems with my GPZ 600 -4cyl twin cam Kawasaki thinking with higher-compression I was running too lean as the temperature needle was running a few mm from the end of the normal range very very close to Hot, (find out my mechanic says all the gpz run hot- after the fact) so I raised the needle in the CV carb one mm and yes the temp has gone down but Im not hearing that same energetic exhaust note , which means too rich :( , ARRRGH!!!!, back to the drawing board
Unfortunately u are not right. The adiabatic flame temperature is actually higher at the equivalent ratio, but, the combustion chamber isn't. You not consider the cooling effect of the gasoline. When you have a lean mixture, the total chamber temperature is even higher than the stochiometric one.
Maybe this is explained in another video, but how do engines control the A/F ratio? Especially when it comes to different throttle levels, RPM, turbo boost etc?
ASE says running lean can be a cause of running too hot, some guy on the internet says running lean makes the engine cooler. Guess who I'm gonna believe?
Nobody would believe me when i told them my Chevy would run ice cold all the time because it was running so lean. It would be above 50 degrees out and i'd have to give it half throttle to even start it and it would just about stall out at a light.
Saying it's lean without reference to a the current AFR, is like using "his" and not referencing to a person first. Since very few people actually run gasoline these days you should swap to 14.1:1 as it's stoich for E10.
Of course i suppose you could technically lean the mixture so laen that the complete absense of fuel would cool engine because it would only be sucking air
Why doesn't maximum power correspond to maximum temperature? A simple temperature entropy diagram would make one think a higher max cylinder temp would produce more power (all else being equal). So, what else isn't equal?
Well, i wouldn't call id a myth, it's more of a misconception. Everyone knows that you need oxygen and fuel for a combustion and naturally a combustion have a lower temperature when there is less fuel to burn. However, the fact that diesel engines are producing more NOx simply because they are running lean should remain the same, right?
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WHY- they say lean burns hot is because running an engine lean (heat damages) the valves and combustion chamber. Metal oxidizes and heat increases oxidation, running rich uses all oxy leaving none to react with the metal but lean leaves a hot chamber with corrosive oxygen. People see scorched combustion chamber an think it’s melted or heat damaged but it’s reacted or rusted away. They are also partly correct because oxidation is a form of combustion and combustion of metal is extremely hot and the oxidation of the metal may also melt and aka run out of control- hotter=more oxidation and more oxidation means hotter till destruction. See thermite as that is a good representation of metal reacting aka combusting. Hope this helps, I could be wrong I am not a scientist. An engine producing NOX is not producing iron oxide or aluminum oxide as the nitrogen is “stealing” the remaining oxygen. Knock is pre detonation where you have a cylinder trying to run backwards- imagine two pistons on 1 crank and 1 says I’m going to turn counter clockwise and the other says clockwise= not good
Have you heard of the ZD30 engine? They like to blow up eg, blown hole through pistons and splitting the head. All the engines seem to do it, so some modify them doing an EGR block to stop the hot gases going back into cylinder 3 and 4, these two cylinders are known to get the holes. In some cases it works but the engines are still blowing up. They just seem like time bombs, does the EGR block off do anything? And what can be done to stop these engines blowing up?
The peak of NO2 is around 15.5 to 16 A/F, not 15, so basically your engine can go lean and get your engine hotter. Your graph is incorrect mate. saying “lean reduces temp” is really inaccurate.
Hi Jason. Love your videos. Can you please explain to me why a cold engine requires a rich mix to start. Never understood it and nobody can explain it. Thanks a million.
Because the engine is cold, it has cold surfaces in the intake manifold and head so part of the fuel will not vaporize properly when it hits those cold surfaces. So you need excess amount of fuel because part of that fuel will not be in usable form to burn, until the engine achieves running temperature.
so its a matter of matter of "frame of reference" like most things... running lean with stoich as the reference frame runs engine cooler. running lean with peak power as the reference frame make engine run hotter.... so long as you are not beyond stoich where it begins to fall again. I think I get it, Thanks!
In carburetor and manual fuel injection piston aircraft engines @ 75% throttle, the leaning process involves adjusting the mixture until the temperature for the hottest cylinder is just below the threshold for hot EGT for that engine. This normally equates to best range for that RPM/power setting. Would that setting equate to the 14:7 ratio on the graph? At 100% throttle the mixture is set to full rich to keep temperatures down and ensure maximum power. Would that be around the 11-12:1 ratio on the graph?
Here's a Questions: At wich A/F does the highest horsepower occur? In what way would you think the air in a combustion chamber brings down the temperature? (For trolls: if someone blows air at a gasflame it will become hotter: treu or false?)
If your graph was correct, it would mean that diesel engines would emit far less NOx than gasoline engines, because of the leaner air/fuel-mixture in diesel engines. Why is the complete opposite the case? Plus you didn't explain at all, why excess air in a lean mixture cools the cylinder. You simply said "it does". You sadly failed to explain the question in the video title fully.
Great explanation Jason! That makes sense! I did an egr cleaning video where I said injecting exhaust gases cools the cylinder temps and people were not understanding. I will reference them to this video now!
I'd like to see it Chris
Just want some advice sir,, my forester 16 at 60k km is starting to show idle problem.. only at warm start, rpm drops low (almost stall) and bounces back up.. at cold start its idling normally high as cold engine then gradually drops.. the problem usually only occurs at warm, like after a long trip and engine rest for an hour,. Any advice sir,, where to look first before I bring it to mechanic.. thanks. More power
Thats only if your vehicle has an EGR cooler. My 2011 jeep grand cherokee does NOT have an EGR cooler.
Markus Mordeno i think it might be a crank shaft position sensor
I am definitely using this explanation next time this debate comes up. You make me sound smart!
I think the running lean/hot originally came from the 2 stroke dirt bikes where the gas and oil mixture lubricated the engine. Running a super lean mix (more power) would cause the engine to seize up from lack of lubrication. In this case lean=hot from lack of lube=engine meltdown.
In conclusion - if you're ideal then you're not cool
Hahaha you could not have said it better!
The women say the ideal man is a douche.
I think you got all this wrong. First fuel acts as a coolant itself. Then a lean mixture will behave like a burst in flame instead of a controlled expansion then could cause knocking, and not by having another hot spot in the cylinder. The lean mixture will ignite too quickly and try to stop the piston to reach TDC that causes knocking. This is why cars have knock sensors that will retard the ignition in that case. So having too lean mixture will retain the heat longer into the cylinder, make the engine work harder and will make it running more hot.
Too rich mixture then will cause it to continue burning after power stroke and dissipate heat into the exhaust valve and the pipe. So there is a sweet spot to get that is called "well tuned engine".
I am viewing this video from the point of view of a general aviation pilot (in flight sims only!!!). For MOST piston aircraft the mixture is left up to the pilot. Full rich for takeoffs and landings, and since most of them are air cooled, the mixture is set to control Exhaust Gas Temp and Cylinder Head Temp. For climbing, somewhat rich, and for eco-cruise, somewhat lean of peak temp. Pull the mixture control out until just past peak EGT. The engine cruising is making less heat due to the throttle setting being reduced after climbing, so lean of peak doesn't cause overheating of the cylinder head. I think some planes have automated this, and I feel all should! The pilot already has enough to do! This needs to be adjusted constantly as the plane climbs higher. ( The higher you climb, but more you need to pull the control out.)
I had my Prius Prime up to 14,??? feet at Pike's Peak, and never had to adjust anything. 15K' is the ceiling for most naturally aspirated piston aircraft, so my Prius outclimed most of them with no adjustments on my part. (Or in any car!). Of course no cars currently sold that I know of are still air cooled as most GA aircraft are. The Cessna 152 starts struggling at 5K' (in my sim, I have never flown any plane IRL). My 182 Turbo craps out at around 22K, but is way happy over 15K. Very necessary flying in Papua and Papau New Guinea, or Chile.
Thank you for this video! It looks like people in the comments that disagree are mostly not watching the whole video or are not opening their mind to the fact that there is a big difference between the technical term "lean" and the garage tuner's term "lean."
you mean like garage tuner's lean doesn't refer to the knoking problem?
@@kevinghifari2330 I think he means the technical term lean indicates running above the stoichiometric ratio, where temperatures will be cooler than at the ratio. What a tuner means by lean is below stoichiometric, but above a ratio of 11-12, where the temperatures will still be rising the leaner you get until you get to above 14.7 (which in practice most current cars will not reach in WOT situations).
Agreed. People use "lean" as a relative measure, not by using the stoichiometric measure of ratio. In a way, they are being correct, but they aren't using a technical term.
here is my video video on perpetual motion engines
Lean means higher combustion temps; that's why lean mixtures are responsible for creating NOx. Fuel droplets evaporate as they enter the combustion chamber, lowering charge temperature. This is one of the advantages of E85 fuel, as the lower energy density requires increased volume, which in turn lowers charge temps further. The engine running
"cool" or "hot" has nothing to do with the mixture. That's a function of the cooling system.
Governments, manufacturers, and chemists will all disagree with him.
Fail a tail-pipe "sniffer" smog test for high NOx, the answer is always the same. Lean mixture.
Either address the lean condition, or fix the EGR system designed to lower cylinder temps and drop the smog.
When I saw a lean engine, I thought about an engine running on lean. The drink. Whoops
On some simple prop airplanes they have a mixture lever to lean or rich the fuel to air mixture, because the higher you go the less air there is/ less fuel you need. Richening the mix is also used to help cool the engine-- I was once flying on a hot day, left the fuel full rich, barely maintained max allowable temp and saved the day. The end
Pressure and Mass Fraction vs. Rotation.
Otherwise known as the “sweet spot”.
Ignition timing for power when lean means more advance in the ignition timing. Why?
Because, leaner mixtures burn much slower. Therefore, the sweet spot just past TDC needs to have more ignition advance so, the pressure is present at the same time as it would have been. It’s the other side of the equation.
If you do one thing(leaning the mixture)one must consider the other changes this creates and allow for it. In this case it’s more advance for the ignition event.
David Vizard Performance has stuff on this.
You guys will love it.
Actually, people say that running lean causes increasing the EGT. Because, lean combustion is slower than the rich combustion. That's why combustion speed is decreasing and combustion shifts towards to BDC. Exhaust valves are opening before BDC. Then you are exhausting the gas that just completely burned or already burning.
Yes this is also why your headers turn red hot if you lean out your a/f mix.
@@B10401 You can only advance timing so much until you run into detonation issues because you are igniting the charge while it is still getting squeezed for a while. You also loose mechanical advantage. The leverage the rod has on the crank is the lowest at TDC. TDI's exploit increasing mechanical advantage by putting in the fuel in pulses so that the fuel burning happens after TDC as well as mechanical advantage is increasing.
Also engines don't run at an ideal. O2 sensor feedback is switching based. Your engine is actually running a bit lean and then a bit fat compared to the ideal over and over again as the O2/Fuel air sensor switches back and forth. You'd need a sensor on each exhaust port and individual exhausts as well as TDI to even try to run at a constant ideal mixture for the engine design.
But in summation the problem is EE here is saying ideal is stoichiometric ideal. When in reality ideal is the ideal ratio for the engine design. When someone says leaned out and got too hot they aren't saying it went over 14.7 A/F they are saying it leaned out compared to the ideal design ratio which can be anywhere from 11-14 for the engine.
@@B10401 Yes, I am thinking mostly the same. If an engine is running Lean, meaning there is a greater part of air mass for each amount of fuel mass, beyond the stoichiometric ratio, the mixture should (from what I can suppose) burn faster, as it would be "easier" for each fuel molecule to bond with an O2 molecule because these are in excess. Still I do think poor mixing is the main reason why an engine may run hotter, considering not every fuel molecule can bond with its corresponding O2 molecule properly, resulting in greater fuel consumption and a reduced effective power (power produced for a specific volume of fuel burnt).
Combustion velocity will decrease on both sides of stoich as well
@chaser27 Combustion velocity is maximum at slightly rich mixture. It's the same nearly all kinds of fuel.
I’m only a kid interested in cars and whatever that has an engine. Sometimes your videos make mot much sense to me but I still watch it and look at your fantastic drawings. Good work Jason :)
Hey i have a fun topic. Engine power is greater with colder air. What are the rates for atmospheric and forced induction horsepower bumps summer vs winter.
It would make a fun video!
Power is not, in all cases, greater with colder air. Humidity will combat the colder density. That is why density/ altitude is used to calculate actual horse power. I.E. you will make less horsepower in Colorado at 30° than in Maryland at 60°. Because of altitude and air density.
@@yinzer_412_ Think he was saying something more like Maryland at 60° vs Maryland at 30° and the effects on both N/A and forced induction. Furthermore, i would also like to see N/A vs turbo vs supercharger. Then throw in humidity to talk about molecular weight while we're at it.
In all cases N/A will have bigger gains over power adders when the D/A is lower. This would make a good video for everyone to see the difference.
65° at about 23% humidity is pretty much the perfect condition for a dyno test. Yes, air is more dense when colder but that requires more fuel. Fuel that has to be more reactive to ignite the colder air. This typically requires a lower octane. Thats why E85 guys always have somewhere between E40 and E60 in the winter time otherwise the car may misfire. In a nut shell the extra fuel needed for ignition will actually take up more volume in the combustion chamber. It has to be more reactive (lower octane) and there has to be more of it. Not good for HP because its like the car is running rich just to operate.
I have a 2011 CTS-V and live in hot ass GA. I know it feels like alot of power loss when its 90 and above vs 50 during winter.
I think the thing he overlooked was having a lean mixture means there is more oxygen in the cylinder which produces a faster and hotter flame-front, thus, overheating. Engineers have spent over a century studying this and I tend to believe them
Only a hotter flame front if there is fuel to use with that oxygen. If there is extra oxygen then needed for perfect combustion that won't make the flame front hotter. You would just have unused oxygen.
@@Alobster1 That's not how it works. Oxygen is an accelerant- the flame absolutely burns hotter and faster when a higher concentration of oxygen is present.
@@UncleDon226 Sure maybe faster but the overall amount of heat from the fuel burning is going to be the same.
Its not about oxygen, fuel acts as a cooling agent, so when ran lean, there is no extra fuel in the combustion chamber, also coolant circulates around and top of the engine, not inside the engine's combustion chamber to cool down, same for the oil, it's lubricates inside the piston rings area, so when ran rich, there is extra fuel available which takes the heat away from the engine 😀
@@UncleDon226 You said it yourself. "faster and hotter flame front" more heat over less time doesn't mean more overall heat.
Basis of his argument is that any mixture < 14.7 : 1 is rich
People say your engine is hot because it is too lean, which does not mean > 14.7 : 1 e.g. 14:1 is too lean
It's just how language works.
Exactly, I see a lot of people on here not understanding that. Lol next video there's going to be people wanting EE to pay for their blown engines...
Exactly. "Lean" is not the same as "too lean for what you are trying to do with it".
TL;DR of video: "lean relative to ideal stoichiometric combustion" is different to "lean relative to ideal AFR for maximum power which can still be technically rich of 14.7:1"
14 - 15 is the deathzone. It has the hottest EGT's. Combine that when under load.....BOOM!
It may not make the engine hot, but it makes the exhaust manifold glow red.
It will toast the engine oil prematurely. And burn the engine if it's not closely dial in .
I think it comes from the aviation community, running rich (of peak) and running lean (of peak). In somewhat older planes you usually have manual mixture control, and in even older planes with engines that have carburators, you could not lean the engine to much due to uneven fuel distribution in different cilinders, which could cause overheating of certain cilinderheads. In fuel injected engines, there is no uneven fuel distribution into the cilinders, so running lean of peak in fuel injected engines saves gas, carbon build-up and reduces emissions
If you extend the second graph (x axis) to show more lean ratios (>15) the temps go down again. It's called lean-of-peak (LOP) that leads to lowest emissions and best economy (for a minor power loss) used in aviation
The Fuji triple 750 2 stroke in the 1990s polaris watercraft all had a design flaw: the 3 carburetors for each cylinder were hooked up in serial from a single-output fuel pump. After one season on pump gas, an owner would park the craft for the winter, start it up the next summer, take off skiing and within 5 or so minutes break down having burned a hole in the piston on the last cylinder, due to ethanol gunk clogging the previous two carburetors and starving the 3rd for fuel. Less fuel means less cooling effect, which is what people are referring to when they say "lean runs hot". it simply means "if you lessen the fuel, you'll create a hotter cylinder" not "if you're technically lean compared to stoichiometric, you're hotter than rich compared to stoichiometric" That's a meaningless statement anyway, because who cares? Perfectly stated, would probably be, "you're running rich obviously, but if you reduce that richness in the direction of leaner, you'll move more toward ideal ratios, and increase cylinder temps, and can damage your equipment, even if you were still technically "rich". Edit: the fix for the fujis, is to buy them cheap with burned pistons, rebuild the engine, and replace the single output fuel pump with a 3 output, and plug all carb outputs.
I'm not that sure about your hard statement: Running Lean does increase temperatures, but inside engine, specially inside combustion chamber, this can put alloys and lubrication under excessive stress and strain, also, higher combustion temperatures, higher flame temperatures, increase NOx emissions, as you pointed.
Many approaches have been attempted, from Water Injection in WW II Aircraft engines (see AEHS), to tactics as in SAE papers: 860533 (EGR); 741091 (Cooling liquids); 840237 (Ethanol, E10); to patents, such as Utility Models ES0220611; ES0248478.
If you can't be consoled, is because you don't want to.
I think the video started out good good but u started stumble at around 6 min. in. Matt @ the workshop does a great job elaborating on the topic.
Jason,
Another great video and spot on correct with all your facts (if we ignore the EGR acronym mistake that you corrected in production).
From reading the comments below it still seems that there are many people who struggle to understand the difference between "less rich" and lean.
Little bit lean mixture results in less vaporised fuel in combustion chamber and runs a bit hotter and thus producing more NOx emissions in gassoline engines. Have been waiting for this line, but it never came. However thats what they teach you in the school and there are plenty of A/F vs NOx graphs on the internet supporting it.
Seems like a very nitpicky conclusion. Running lean increases cylinder and exhaust temperatures, which the graph on the right shows, even though the "technical" answer is that the flame itself burns cooler both lean and rich. Running lean runs to knocking which causes pitting and can damage the catalytic converter from hot exhaust gasses, so saying "running lean causes higher temperatures" is a valid thing to say.
Great video Jason. Please can you do a diesel specific version and the challenges with balancing out efficiency, NOx and soot?
Is it better to accelerate a diesel in a lower gear rather than a higher gear from a soot perspective (vs fuel efficiency perspective)? Thanks!
Yes!!! Please
Being able to measure peak EGT is crucial to getting this right. Running a turbocharged aircraft engine at higher rpms than book, leaner settings than book takes extra tuning but can totally change an aircraft's performance envelope.
Theory sounds great. Now please explain why in flight training we are taught AND SHOWN that we can try to conserve fuel in flight by leaning out the mixture--until the cylinder head temp gauge starts to show it is too hot. You're missing something here, the flight instructors and the gauges don't fib.
Because you are leaning out from a rich condition to closer to ideal. So the temps go up.
@@scottyh72 , totally wrong. When the combustion temperatures maximize, then the least amount of heat is conducted to the engine because the explosion is MUCH faster, more efficient, more powerful, and shorter duration. An ideal maximum explosion is far to fast to be able to heat up the engine much at all. It is a weak and slow combustion that conducts the maximum heat to the engine. And in fact, excess oxygen is extremely corrosive at under those conditions, and you will melt pistons and valves. The way to make the engine run coolest and last longest is by achieving the highest possible temperatures, which then are exploding so efficiently that there is no time for hardly any heat to be conducted to the engine.
@@scottyh72 90% of this is a semantics problem - Jason was using rich = richer than stoichiometric and lean = leaner than stoichiometric, but as he states, stoichiometry is not really a target for internal combustion engines. The alternate definition that causes trouble is rich = richer than best power and lean = leaner than best power
School them Lyfan. The video and title is just misleading. Needs to be more specific with the level of lean he is talking about and not just point blank lean.
@@kirkaugustin2232 He's not totally wrong he's absolutely spot on, you still misunderstand what he said, the video and how this whole temperature variation with AFR works.
Air planes run rich, because a rich engine is less likely to stall. When cruising a pilot can increase air/fuel ratio to improve efficiency, and when doing so is taking the engine from rich to stoichiometric which is where temperature peaks. Air plane engines (piston ones anyway) never run lean, they run slightly rich to very rich.
I can think of at least one mechanism through which, leaning the mixture will increase the *exhaust* temperature:
My understanding is that leaning out the mixture slows down combustion. The slower the heat is released into the combustion chamber, the less time there is for this heat to be extracted as a mechanical work by the piston. An extreme version of this effect is turbo antilag by ignition retardation - if you don't extract the energy, the heat stays in the gas.
Now the question of how big this effect is depends on how much is combustion slowed down by a lean mixture in the real world. I don't have any numeric data on this but I remember that leaning out the idle screw on my wr450 would cause the exhaust header to glow just when idling.
It would be pretty cool to see if you could cover combustion speed and how it changes with the AF ratio.
Cheers and thanks for all your awesome content!
The first thing that came to mind is that you have to set engine tuning aside.
Stock engine is built to run around 14:1 and it will survive. But if you have for example a 9:1 compression ratio and put like 1,5bar of boost on it, it will fail due to hot combustion. By running lean in tuning prospective is running above 13:1 which is not lean in normal cases.
Edit you mentioned my point in the end.
An unloaded diesel engine is a prime example of running lean and having low combustion temperatures. As throttle is increased, ideal ratio is approached resulting in higher temperatures.
My personal experience attests to the ~12.5 or so wide-open throttle AFRs in N/A applications, and often ~11.5 in turbocharged applications we end up at. I'm very well vetted in my platform (Mazdaspeed 3), and when we tune we almost always end up ~11.5 or so on 93 and ~12.0 or so on ethanol mixes to stave off knock (in wide-open throttle regions; cruising regions we always shoot for stoichiometric). We've learned that going leaner than these can cause ring-butting and cracked ringlands due to cylinder heat. Being DI, we know that the extra fuel spray does cool combustion temps even more because it's injected directly into the combustion chamber, which is why we empirically see lower knock in the telemetry when doing so (in part).
Additionally (and maybe outside of the scope of this video), ignition timing can have a dramatic effect on cylinder temps. Have you (or will you) made a video on this?
In general aviation pilots control their own mixture in the plane. We do this because as we get higher there is less air, therefore we don't need as much fuel going into the engine. I bring this up because the common way we lean the engine is to pull the mixture back (lean) and watch the EGT. When we hit peak EGT we will then push in the mixture (rich) again watching the EGT and then stop when we get 50 degrees cooler on the EGT. This is called being rich of peak. It'll generally give us our best power, and best range. But there is a thing called lean of peak. Some planes are ok being flown lean of peak, some are not. But as you can guess when we are at peak EGT we lean out a bit more, and the EGT will start going back down. Flying at peak EGT or lean of peak will give us best endurance.
I was modeling an engine trying to use boost/back pressure rather than throttle to moderate output and it kept showing that if it went lean, it actually ran cooler at the exhaust, even if it was compressing more air at a high CR. Hence, I found your video for a second opinion. Thanks!
We used to intentionally lean out our mixture in go-kart racing. Get a little more RPM but the temperature would climb. Had to turn it back after making the pass or you would overheat. Don't know if it was the RPM or the mixture that caused it to get hotter, but it did get hotter. That was running on methanol. Could just be the case that the air cooled engines couldn't handle running at peak mixture.
And that's coming from the driver that actually physically turned the mixture screw while driving and watched (and had records of) the tach and engine temps. It's not an "I heard they did this..." thing. We really did it mid race to make passes and if you forgot to turn it back out you had about 2 laps before your overtemp warnings were going off... maybe. That would happen sometimes if you didn't manage to make the pass.
Also, my dad hated this and would remove the coin I stuck in the mixture screw to adjust it every so often... lol Just jam a penny or nickel (depending on which carb you had) in there and boom, it's a finger knob.
that dates back to carburetor days...i had a 1987 xr600 that ran much cooler with bigger jets but of course an old air cooled engine with two carbs dumping gas into a giant single is nothing like anything today
Did you watch the full video before you wrote your comment? No? Watch the full video, then comment.
Boosted Films bless you! 🙏🙏 Haha
But I'll forget whatever garbage I have to comment after I finish the video!
@@fancyyahoo Watched it all saw no justification for unburned oxygen cooling cylinder temps.
@@tangles01 Having much less fuel means there's less energy to heat up the cylinder in the first place.
If you run lean and create a knock then it will run hotter. It's the same as advancing the timing. The burnt gases will spend a longer time in the combustion chamber causing the engine to run hotter.
This can be demonstrated easily when flying an airplane with EGT and CHT gauges. We basically use this to set our air-fuel mixture. Good video.
Anyone who flies a piston-driven propeller airplane knows this to be true -- when you set optimum cruising power, you adjust the air/fuel mixture until you see peak exhaust temp.. Make the mixture richer *or leaner* and the exhaust temps go down. There's a point -- stoichiometric -- where exhaust temps are maximum.
You can draw all the cartoon pictures you want to explain this using every bit of science you can think of. But out here in the real world.......because I've seen it many times.............a lean engine can (and usually does) actually run hotter. I just had a Ford 5.4L in my shop with a low fuel pressure issue. The codes in it were for lean running conditions for bank 1 and 2. Its also had codes P1299 and P1285 (Cylinder head temps to high). The customer also told me that the coolant temp gauge was up way higher than it usually is. We fixed the fuel issue and the high cylinder head temp codes did not come back. This is just one example of many that I've seen.
Back when I was at a place with a Dyno, we did some egr testing on my old Datsun 720. It had extensive engine modifications but we found a 7rwhp gain with lower emissions (didn't test NOx) with the EGR blocked. I miss that little truck.
Do I have to worry about this with my Toyota Celica?
Its a toyota. Feed it fish once a month and you ll be fine
Only if you have 50 years experience. ;)
No your 32 years old Celica is immune to that!
Engineering Explained 51 years lol
Not if it's a 1994. Tehe.
It's my belief that "Lean vs. Rich" in regards to temperature is arbitrary, and subject to vernacular. In the construction equipment service industry, running "Dead Lean" refers the perfect combination of air-fuel, making for 100% ignition, and exhibiting a blue exhaust flame from the typical short systems on non-catalyst engines, such as on compressors and aerial work platforms. It also produces peak running temperatures. More specifically, this is in reference to gasoline engines running at optimal high rpm that coincide with the peak of the torque curve, and under a steady load. In my case, this would involve a prime mover turning single or stacked hydraulic pumps.
From my perspective, the subject is more about semantics than it is about NOx production levels, but this is a good study of stoichometry, and a fine presentation.
On injected aircraft engines, running LOP (lean-of-peak) is a standard practice. It's a great way to increase efficiency.
Running lean may cause a slower flame travel, thus the af mix may still be burning when the exhaust valve opens. This causes a hot exhaust valve and hot exhaust headers.
Im not sure, but a lean mix flame front may slowly progress away from the spark, causing the extra air to compress and heat sufficient to ignite the af mix, thus causing the second flame front diagonally from the spark plug, thus causing knock.
Another possibility is that the now hot exhaust valve causes a second ignition thus causing a knock when both fronts collide.
Kunal Shah that's the problem it may cause the flame to occur in the exhaust manifold, but it doesn't
Kavi4 the exhaust valve opens when the flame is still burning, in a slow burn mixture
I just realized Flight Simulator kinda models this with the cessna, as you enrich it, temp goes up then back down. I was reading online about a month ago how the highest EGT is most efficent. Thanks for the awesome video man!
Jason,
some time ago I got a wideband O2 sensor onto my GX390 go kart engine, in order to tunemy needled carburator... I realized then that running a misture above 1.00 lambda (and knowing that 1.00 lambda = 14.7 air/fuel ideal ratio), the engine simply cuts, simiilarly to a ignition cut... The engine simply stops to generate power, as I said, like if I turned off it while running... That was the exactly feeling I got when lambda got higher than 1.00 on the O2 display sensor...
I concluded that no engine can run with a mixture above 1.00 lambda, and so, all mixtures we can work on are less richer (closer to 1.00 lambda) or more richer (values smaller than 1.00), but all mixtures are always richer from this lambda perspective... Using this perception and what you said on your video, it makes sense to say that a lean mixture makes combustion chamber temperatures to be high... But this lean mixture is, in fact, a rich mixture closer to the 14.7 (or lambda 1.00).... Does this make sense??? And is my conclusion that no engine can run proper on O2 sensor readings above 1.00 (real lean mixture) correct???
Cheers and thanks for this excelent engineering channel!!! I really enjoy your videos!!!
I am glad you made this video. I had a mechanic tell me that running lean was going to make my engine explode.
JohnnyMo Which is why I’m glad he posted this, it reassured me I wasn’t being mislead. :)
Heat output is a function of amount of fuel burnt and efficiency of combustion, will create same temperature curve... alternate explanation for temperature curve explanation.
Happy 2019 to Engineering Explained!
Thanks, happy 2019!
This video is pedantic. The temperature increases up to around 15:1 and then plummets. It plummets because the engine will not run correctly, therefore the statement 'lean engines do not run hot' is wrong because it does run hot' in the region where the engine actually still runs. Anyone running a lean engine that still performs will see a temperature increase. You've countered the false statement that 'a lean engine runs hot' with another false statement that is ' it does not run hot' both are wrong as they don't account for eachother, but in the practical world with engines in the performing regions of afr ratios they will run hotter.
My R1 came with a full Akropovik exhaust system but didn’t have a power commander or ECU flash. It’s like riding an oven. I’ll get a fuel controller one of these days. At least that’s what I keep telling myself.
Hey Jason, here in the UK pretty much everyone with a diesel car has it tuned, often finding about 15-20% extra power. There has to be a downside-surely! There is an real lack of science available as to what's happening in the car, plenty of stories but not much fact. How about a video talking about it? do they start pouring out NOx, start wrecking bearings etc. etc. Also if they could perform better why didn't they do it from the factory.
That is not what the exhaust valves and exhaust manifold said....... running "lean" makes your egt's hot. More fuel in exhaust = cool, less fuel in exhaust = hot. If an engines cooling system is really efficient (usually they are not), then it will keep a engine cool untill it passes it's efficiency threshold. The after effects of running lean is what makes everything hot or over heat, hotter under hood temps, hotter exhaust components, hotter cat converter, and hot oitside temps = overheated engine.
Just my .02 cents worth working on cars for the last 17 years or so.....
Remapping your egr from working makes your much nicer to drive.
What's the effect of running up to 10% petrol in a diesel engine according to the owners manual in very cold climates?
Nowhere do you talk about the length of TIME for a lean charge to burn.
Lean does indeed make engines run hotter because the charge takes a far longer time to burn, thus bathing the engine's internal surfaces in more heat. Your graph is wrong, temperature rises considerably lean of 14.7 A/F ratio. I've seen piston's from a friend's Suzuki sport bike which had partially melted surfaces simply because he installed a sport exhaust but didn't think it was necessary to re-jet the carbs in order for the fuel to match the increased portion of air.....
So if we are able to decrease cylinder temperatures by adding more air into the combustion chamber, then why do we use EGR gas, since its main role is to reduce NOx by decreasing cylinder temperatures? I mean, by making the air/fuel ratio lean we can reduce temperatures as well.
I actually really like this guy
Zoltan, yes and he'd make a great model at 19n, but he's married to a female.
Sorry buddy but this is wrong. Other comments deal with one of the reasons why but there is also an interaction between AFR and ignition timing which causes even further temperature rise when running at high loads. Note also that almost no gasoline engines run lean of stoichiometry when hot due to the AFR requirements of the three way catalyst. Please do a little more research on this topic and demonstrate your integrity by posting an update. Thanks
Jason, it would seem the maximum temperature would be reached on the rich side of the stoic ratio, followed by the subsequent decline. According to your description of the ideal stoic of 14.7:1 not providing real world homogenous mixture of gas and air (hot vs cold pockets in the combustion chamber) to achieve complete combustion, lowering the A/F, up to some point, allows "all" the hydrocarbons to be combusted. This should lead to an increase in chamber temperature. Now, if thereafter you reduce the A/F, you then run into excess fuel that will not be burned, and will necessarily withdraw heat from the chamber through the fuel evaporation process, as you described.
Am I interpreting the scenario correctly? Thanks!
I've seized a number of engines over the years. I've always called and learned it was due to running too lean. Funny how you explained it as not rich enough causing the rise in temps. Melted 2-stroke pistons result from high temps and the not rich enough allowed me to see why. Still, I've always called it running too lean.
no citations = don't listen.
@@wolu9456 you don’t agree with the video?
Older engines with no EGO sensor and no computerized ignition did run hot when lean. Lean burns slower and higher throttle takes away vacuum timing advance. Slower burn means flame, even though cooler, has more exposure to coolant given the greater capacity to pass heat into coolant through cylinder walls. The engine management systems of the last few decades would have check engine light on and would have controlled the situation and limited ill effects. Like many things, old ideas die hard.
I have experimented with a carbureted engines and only observed the highest temperatures on stoichiometric AFRs (and a bit richer). Never observed an engine running hotter on lean AFR.
Let me guess, you don't like new tech and newer cars either?
dosmastrify exhaust gas oxygen
My point is that this is no longer happening but it is not an unfounded urban legend. Years ago I worked in a GM dealer I’m the truck shop. C20 through C65 trucks running in the hills in my area would run hot even in cooler weather when they had the very common faulty fuel pumps with the return line that many big blocks and small blocks used. The driver would keep the pedal matted and drive a fuel starved vehicle up the hills and have gauges climb. The complaint of temp gauge going near the top would go away with a new pump and also return line restrictor and fuel pressure to carb staying at over 3 psi wide open loaded up hill.
Ante Radić no, I had a tech support and training role with a car manufacturer until a few months back. I was in that job for 30 years. My post was to address that this was not urban legend completely as older technology would overheat when lean with no other methods in play to limit the effects.
You didn’t bring it home till the last couple of minutes... As you stated, the nomenclature is based off the optimum ratio (not stoichiometric,) and thus “lean is mean” and “lean is hot” hold true.
Why go to school when you can watch EE
interested to hear your opinion, as far as i care lean is bad, i have welded a spark plug to a piston before from running too lean
The stokiometric ratio is the most efficient mixture of fuel and air needed to create and explosion without waste , but engines are tuned to run slightly bellow that to create a slower more controller burn that the engine components can withstand , this also prevents pre-ignition of the mixture as the engine temperature and pressure are enough to ignite a perfect mixture. So running Lean in engineering terms for an engine will definitely make it run hotter. The engine will make more power and respond better but it will fail at some point.
According to Heywood, peak combustion temperature should be just rich of stoich.
It is, problem is though, if you go torwards stoichiometric lean the spark plug will have trouble ignite the mixture. so you go torwards rich to keep the temperatures in check. What is often called "lean" means from rich more torwards stoichiometric.
Okay that makes sense, I was disagreeing at the beginning although the science makes sense.. In the end it's about technicality.. you can say "running lean-ER than stock will make your engine over heat" and that's true.. and that's what most people mean I guess.. but thanks for clearing it up
Correct. Had a lot of people asking about my videos on NOx emissions reduced by running lean, and running cooler, saying they thought lean meant hotter, hence this video. :)
Wow............just wow, amazing video friend, ...I was having tuning problems with my GPZ 600 -4cyl twin cam Kawasaki thinking with higher-compression I was running too lean as the temperature needle was running a few mm from the end of the normal range very very close to Hot, (find out my mechanic says all the gpz run hot- after the fact) so I raised the needle in the CV carb one mm and yes the temp has gone down but Im not hearing that same energetic exhaust note , which means too rich :( , ARRRGH!!!!, back to the drawing board
Unfortunately u are not right.
The adiabatic flame temperature is actually higher at the equivalent ratio, but, the combustion chamber isn't. You not consider the cooling effect of the gasoline. When you have a lean mixture, the total chamber temperature is even higher than the stochiometric one.
4:42
*Warren G Regulate starts playing*
Maybe this is explained in another video, but how do engines control the A/F ratio? Especially when it comes to different throttle levels, RPM, turbo boost etc?
Hi Jason: How do you burn oxygen? 3.07 😜
Btw I’m impressed by the length of your recording takes!
Also the cold gas seems to cool the piston / chamber
this video answer my question perfectly.
ASE says running lean can be a cause of running too hot, some guy on the internet says running lean makes the engine cooler. Guess who I'm gonna believe?
Nobody would believe me when i told them my Chevy would run ice cold all the time because it was running so lean. It would be above 50 degrees out and i'd have to give it half throttle to even start it and it would just about stall out at a light.
Saying it's lean without reference to a the current AFR, is like using "his" and not referencing to a person first. Since very few people actually run gasoline these days you should swap to 14.1:1 as it's stoich for E10.
Thanks Jason!
Of course i suppose you could technically lean the mixture so laen that the complete absense of fuel would cool engine because it would only be sucking air
Why doesn't maximum power correspond to maximum temperature? A simple temperature entropy diagram would make one think a higher max cylinder temp would produce more power (all else being equal). So, what else isn't equal?
Very nice explanation as always!
Great video, great for procrastination. Subscribed.
Thanks for subscribing!
But what about twostroke engines? Running lean means less oil, so running lean would harm a twostroke engine?
Well, i wouldn't call id a myth, it's more of a misconception. Everyone knows that you need oxygen and fuel for a combustion and naturally a combustion have a lower temperature when there is less fuel to burn. However, the fact that diesel engines are producing more NOx simply because they are running lean should remain the same, right?
WHY- they say lean burns hot is because running an engine lean (heat damages) the valves and combustion chamber. Metal oxidizes and heat increases oxidation, running rich uses all oxy leaving none to react with the metal but lean leaves a hot chamber with corrosive oxygen. People see scorched combustion chamber an think it’s melted or heat damaged but it’s reacted or rusted away. They are also partly correct because oxidation is a form of combustion and combustion of metal is extremely hot and the oxidation of the metal may also melt and aka run out of control- hotter=more oxidation and more oxidation means hotter till destruction. See thermite as that is a good representation of metal reacting aka combusting. Hope this helps, I could be wrong I am not a scientist. An engine producing NOX is not producing iron oxide or aluminum oxide as the nitrogen is “stealing” the remaining oxygen. Knock is pre detonation where you have a cylinder trying to run backwards- imagine two pistons on 1 crank and 1 says I’m going to turn counter clockwise and the other says clockwise= not good
Have you heard of the ZD30 engine?
They like to blow up eg, blown hole through pistons and splitting the head.
All the engines seem to do it, so some modify them doing an EGR block to stop the hot gases going back into cylinder 3 and 4, these two cylinders are known to get the holes.
In some cases it works but the engines are still blowing up.
They just seem like time bombs, does the EGR block off do anything? And what can be done to stop these engines blowing up?
The peak of NO2 is around 15.5 to 16 A/F, not 15, so basically your engine can go lean and get your engine hotter. Your graph is incorrect mate. saying “lean reduces temp” is really inaccurate.
Hi Jason. Love your videos. Can you please explain to me why a cold engine requires a rich mix to start. Never understood it and nobody can explain it. Thanks a million.
Because the engine is cold, it has cold surfaces in the intake manifold and head so part of the fuel will not vaporize properly when it hits those cold surfaces. So you need excess amount of fuel because part of that fuel will not be in usable form to burn, until the engine achieves running temperature.
@@loverboy8476 thank you that makes perfect sense.
@@brendankohler1000 no problem brother
so its a matter of matter of "frame of reference" like most things...
running lean with stoich as the reference frame runs engine cooler.
running lean with peak power as the reference frame make engine run hotter.... so long as you are not beyond stoich where it begins to fall again.
I think I get it, Thanks!
Nice information
how does a car start to run rich without any outside influences like modifications?
In carburetor and manual fuel injection piston aircraft engines @ 75% throttle, the leaning process involves adjusting the mixture until the temperature for the hottest cylinder is just below the threshold for hot EGT for that engine. This normally equates to best range for that RPM/power setting. Would that setting equate to the 14:7 ratio on the graph?
At 100% throttle the mixture is set to full rich to keep temperatures down and ensure maximum power. Would that be around the 11-12:1 ratio on the graph?
So if you reduce the compression ratio you can get away with a leaner mix without NOX or knocks. Confused yet?
Here's a Questions: At wich A/F does the highest horsepower occur? In what way would you think the air in a combustion chamber brings down the temperature? (For trolls: if someone blows air at a gasflame it will become hotter: treu or false?)
In what scenarios would it run that lean? I can see that happening under cruising only I guess
How about a video on microwave ignition systems?
How about the exhaust? Doesnt it get hotter?
why don't OEMs target a leaner A/F ratio of say 16:1 at idle or Part throttle since NOx emissions are a lot lower?
Sometimes they do (like Mazda), however lean mixtures tend to be less predictable and burn slower, in addition to producing less power.
How do you prepare for these videos? Is a lot of your information already known from past work, or do you do research to prepare? Thanks for a reply!
Research for every video!
If your graph was correct, it would mean that diesel engines would emit far less NOx than gasoline engines, because of the leaner air/fuel-mixture in diesel engines. Why is the complete opposite the case?
Plus you didn't explain at all, why excess air in a lean mixture cools the cylinder. You simply said "it does". You sadly failed to explain the question in the video title fully.