I just stumbled across these video's while trying to learn more about vehicle engines and how they work. I love this kid he explains this information in such an easy way to understand. I subscribed and gave him a thumbs up.
I'm a 3rd year apprentice vehicle technician and my day today at collage was partly about compression ratio and that video made so much more sense than their half hour lecture 😂😂
Very good explanation of air acting like a spring. This is the very principle that engines with cylinder deactivation use to help prevent pumping loss. They realized that if only cutting fuel supply and spark to a cylinder still requires that cylinder to do work (pump) to move air. By keeping the valves closed during deactivation, the trapped air compresses and restores to its original energy state, no net energy consumed.
Yes, it's because adding forced induction increases the internal pressure in the cylinder, so on top of that, with the compression of the stroke, the pressure would be too high, and pre-ignition could occur. By lowering the compression ratio, this can be prevented, while still maintaining high output.
Hey Jason, fellow Mechanical Engineer here. I am doing TONS of research for this engine I am building and I want to recommend a video explaining DYNAMIC compression ratio and comparison against static compression ratio. Maybe that would shed some light to a bunch of viewers and engineers. Hope this inspires or encourages you. Thanks and I love your videos!
It's the displacement of the engine, as you first described. Referencing this video, it'd be the difference in volume between step 1 (piston at the bottom) and step 2 (piston at the top) of all the cylinders.
Typically 12:1 would have more power, if it were the same engine we're talking about, for multiple reasons. First, 12:1 is thermally more efficient, so less power is lost. Second, with more compression, the air has more time/room for expansion, so the power stroke is more effective.
Typically you'll want to use a lower CR with turbos (relative to the NA version of the engine) so that the internals can handle the extra pressure/temps and so you can prevent knock.
Hey dude! This has been said a gazillian times, but I just wanted to go out of my way to reflect the prior comments and thank you for taking the time to teach and explain things in such an easy to understand way. Super appreciated, much respect.
1) Apparently yes, based on Mazda's skyactiv diesel engines. Haven't quite figured this out - may have something to do with expansion ratios. 2) The ones in Europe do, and they have higher CR as well (14:1). Direct injection and the exhaust design help them achieve this. 3) Ethanol? Well I believe ethanol has a higher octane rating (search my channel) which allows for higher CR.
If you wanted to increase the CR of your engine, yeah it could be done with different pistons, or different cylinder heads, or connecting rods, but connecting rods would likely be a complex swap. Regardless it would need to be re-tuned.
They may use stronger pistons, if there is additional stress from the additional compression - it would be fairly application specific. You can alter the geometry of the pistons, crank, and connecting rods in order to alter the compression ratio.
@1971SuperLead Correct; gasoline engines use spark plug ignition, diesel engines use the heat of compression for ignition. I explain in greater detail in my Gasoline vs. Diesel video.
1) I think Mazda said they made their new skyactiv diesel with a low comp ratio because it can more reliably use a lightweight aluminum block and decrease the weight of the car.
Thank you for posting these videos, I don't know much about cars but I am in love with jap cars myself. These video's are slowly helping me learn more about my car and I hope to be able to work on my car at a proffesional level so I can fix any problem and tinker without worry ;). I just don't know where to start :( haha but this is a good start getting to know everything first so thanks!
Sir: You are very generous to explain these concepts for everyone to understand, I really feel grateful to you. One tiny question; How do you increase the internal pressure on the cylinder? And what does it have to do with the CR? Are Honda's engines (for ex the F20C, K20A)greater in this sense than others? Thank you in advance!!
Use the fuel that your car manufacturer recommends. Cooler air is more dense, yes, so everything else being equal, cooler air will have more O2. This isn't necessarily the case at higher elevations.
Change the engine geometry. New internals, domed pistons. It's not usually as simple as changing one thing, you'll have to have a group of components that work together including the crank, rods, pistons, cylinder head, and valves.
I swear, i come to your channel almost daily to watch at least two vids...some i've watched 4-5 times already...don't know a great deal about cars, just basics.
Refer away, I'm always looking for new material to learn from. As far as CR dictating efficiency, my source isn't wiki; that's just an easy one to check, which MOST of the time has accurate information. But if you'd like the source, it's the last book that I've referenced on the FAQ page of my website (see description) titled "Engineering Fundamentals of the Internal Combustion Engine."
You might have mentioned that when the piston is at BDC and ready to initiate the Compression Stroke, that the intake valve (and obviously, the exhaust valve) are closed.
It's the distance from the top of the piston (assuming it's flat) to the top of the cylinder head when the piston is at its lowest point, divided by the distance when the piston is at it's highest point. Once again, this would assume the piston and cylinder head are flat, which they are not. So really you need to measure the volumes at BDC and TDC and divide.
The current compression ratio of your vehicle, yes. If you haven't altered your engine at all, yes, the stock compression ratio. Should be available online or in a user manual.
@IronPump89 Diesel engines have higher compression ratios because they use the heat from compression to ignite the fuel. Gas engines use a spark to ignite the fuel, so lower compression ratios are used; otherwise the fuel would ignite at an undesirable time. Yes, direct injection on gasoline exists and is now common, but a spark plug is still used to ignite the gas so lower compression ratios are still used. Though Mazda has incredibly achieved 14:1 in the Skyactiv engine for the Mazda3. Kudos.
Thermal efficiency, theoretically, is determined by compression ratio. Not sure what the equation is, but the theoretical thermal efficiency goes up as compression ratio goes up.
Well direct injection seems to help a lot with compression ratios. In the US the Mazda3's skyactiv engine has a 13:1 compression ratio, capable of using regular octane gasoline. In the rest of the world it has a 14:1 CR and uses premium. Not totally sure how they do it but I know direct injection plays a good role. Also, the R35 probably has a lot more boost than the 1.4 TSI, so a it's logical that a lower CR would be used. Could be wrong on that though.
Lol, so your telling me a 426 Hemi with 13 to 1 compression gets pretty good mileage? At least according to compression ratio? Love the vids man. I really learn a lot! One thing... Hit and Miss? I know how they work, but not sure if you or any of your other subs know how they work. If you don't already have a vid explaining, well here is a recommendation. Hit and miss is really interesting on how they work, and I'm sure people would enjoy a video explaining how they work from you.
No Sindbad. 8/1 is the volume ratio. Say 8 = V1 (volume at bottom dead center) and 1 = V2 (at Top dead center in simple terms piston pushed all the way up) this means the volume of the cylinder was compressed or made small from size 8 to size one. Think of a syringe filled with water lets say. If the top part is sealed (n opening). What do you think will happen when you try to push the syringe plunger up ? Higher pressure because you are compressing the water inside.
perfect mate. I am not thick. I just couldn't visualise what was meant. What the relationship actually was. so you explained that perfectly in the first sentence. Thanks
I suppose it depends on how you increase the stroke. If the stroke increases in length (closer to the crank) and has a larger gap at TDC, then I suppose a lower compression ratio could result. Haven't read up on it or anything though.
The engine is more efficient with high CR, so even though more power is produced, it doesn't necessarily mean more fuel is used. Higher CR means better fuel economy over a similar engine with a lower CR.
Two CRs are important here, geometric and effective. You can have different CR and ER geometric values, look at the Gomecsys crank for a geometric difference, or even the true Atkinson cycle (not what Toyota claim they have). Ways of achieving different dynamic CR and ER are possible with variable valve timing (psuedo-Miller cycle). Late intake valve closing means you get a low CR, but a normal exhaust valve opening means you have the geometric expansion ratio. Did you get my PM?
thank you for this video.. now i understand more about CR and the engine knocking... and why mazda is campaigning so much about their new Skyactiv engine which has 14:1 CR..
@mk91077 Yes, that engine is absolutely insane. And in the states it has a CR of 13:1, with 87 octane fuel. Absolutely phenomenal engineering. Watch my video on octane ratings if you're interested.
Assuming the 10:1 is more efficient than the 9:1, and it's essentially the same engine, with altered compression, then yes, it could be more powerful. But you can't simply use CR to compare engines' power.
Okay, I get what you're trying to say. But point is, higher expansion ratios are not possible without higher compression ratios. Surely, a car with a low CR can have a better expansion ratio than a car with a higher CR, but realistically speaking, there is a relationship, is there not?
Could you make a vídeo explaining the effects of camshaft duration and forced induction in dynamic compression ratio. It is allways tricky for people modifying their engines with longer duration cams and turbo to figure out correct cr and dcr. Thanks
Brilliant. Clear and concise the way I greatly hope a most astute human mind could fundamentally understand engineering as a human endeavor, necessarily being capable of making the detailed knowledge practical to the layman.
Only if your car requires it, use whatever the manual says to use, as that is what the engine was designed for. Going higher than necessary typically will not provide any benefit.
I just stumbled across these video's while trying to learn more about vehicle engines and how they work. I love this kid he explains this information in such an easy way to understand. I subscribed and gave him a thumbs up.
Thanks for subscribing!
+Nafir Alvarez Me too man--great job +EngineeringExplained
Rez "this kid" Chances are that you're a 14 year old Arab kid who wants to get into steroids and sweaty men grunting at the gym.
30 is kid? 😁
@@ArtofReliance l
Thanks for coming back, take it in bit by bit and soon enough you'll know a ton.
I'm a 3rd year apprentice vehicle technician and my day today at collage was partly about compression ratio and that video made so much more sense than their half hour lecture 😂😂
Very welcome, glad you find the channel useful!
Very good explanation of air acting like a spring. This is the very principle that engines with cylinder deactivation use to help prevent pumping loss.
They realized that if only cutting fuel supply and spark to a cylinder still requires that cylinder to do work (pump) to move air.
By keeping the valves closed during deactivation, the trapped air compresses and restores to its original energy state, no net energy consumed.
Yes, it's because adding forced induction increases the internal pressure in the cylinder, so on top of that, with the compression of the stroke, the pressure would be too high, and pre-ignition could occur. By lowering the compression ratio, this can be prevented, while still maintaining high output.
googled engine compression explained and this vid came up first, awesome. keep making more good vids
Hey Jason, fellow Mechanical Engineer here. I am doing TONS of research for this engine I am building and I want to recommend a video explaining DYNAMIC compression ratio and comparison against static compression ratio. Maybe that would shed some light to a bunch of viewers and engineers. Hope this inspires or encourages you. Thanks and I love your videos!
It's the displacement of the engine, as you first described. Referencing this video, it'd be the difference in volume between step 1 (piston at the bottom) and step 2 (piston at the top) of all the cylinders.
Thanks for your vids, for someone who loves cars but isn't a mechanic your explanations are easy to understand. Keep up the good work!
Certainly, but it will take me some time. Traveling now, starting work soon, and tons of requests to fulfill! But I'll get there!
Typically 12:1 would have more power, if it were the same engine we're talking about, for multiple reasons. First, 12:1 is thermally more efficient, so less power is lost. Second, with more compression, the air has more time/room for expansion, so the power stroke is more effective.
Typically you'll want to use a lower CR with turbos (relative to the NA version of the engine) so that the internals can handle the extra pressure/temps and so you can prevent knock.
Good you wrote it. I have been searching for this reason
Correct, to prevent pre-detonation from occurring since the air/fuel mixture will reach higher temps with higher pressures.
Hey dude! This has been said a gazillian times, but I just wanted to go out of my way to reflect the prior comments and thank you for taking the time to teach and explain things in such an easy to understand way. Super appreciated, much respect.
Helpful, short, straight to the point.
1) Apparently yes, based on Mazda's skyactiv diesel engines. Haven't quite figured this out - may have something to do with expansion ratios.
2) The ones in Europe do, and they have higher CR as well (14:1). Direct injection and the exhaust design help them achieve this.
3) Ethanol? Well I believe ethanol has a higher octane rating (search my channel) which allows for higher CR.
I love you, you're the cheat sheet to my life.
Man you have done it again!! ive learned why premium fuel is important and what "knocking" is. and the reason for compression ratios.
Great to hear, that's why I made these!
If you wanted to increase the CR of your engine, yeah it could be done with different pistons, or different cylinder heads, or connecting rods, but connecting rods would likely be a complex swap. Regardless it would need to be re-tuned.
Man you have come SO FAR since this video. Congrats on making it man.... I love your videos they’ve helped me on occasion.
They may use stronger pistons, if there is additional stress from the additional compression - it would be fairly application specific. You can alter the geometry of the pistons, crank, and connecting rods in order to alter the compression ratio.
Your videos are amazing and you explain everything from simple to complex in digestive chunks. Keep it up, and thank you.
WHAAT HE DIDNT SAY HELLOO EVERYONE AND WELCOME
Finn H He’s come a long way
doesn't matter, its informational
@@jpegjake i don’t care that you broke your elbow
9 years old
This is the first video I've seen and I'm triggered because of this, what an unwelcome experience 😭
Studying level 2 motor vehicle at college, these videos rlly help me revise 💪🏽🔥
Lol when people go to school to learn something their father should have thaught them in five minutes...
@1971SuperLead Correct; gasoline engines use spark plug ignition, diesel engines use the heat of compression for ignition. I explain in greater detail in my Gasoline vs. Diesel video.
Came here from ur new video, about VCR engines !! Totaly worth it !!
Really excellent video. Simple and to the point without telling us a long story or screaming into the camera.
Correct, except for frictional losses of course. I do have a video on cylinder-deactivation as well for anyone who's interested.
Met you at SEMA, thanks for this video! I've been trying to get my head around this all day.
+ExcessHorsepower thanks for saying hello!
1) I think Mazda said they made their new skyactiv diesel with a low comp ratio because it can more reliably use a lightweight aluminum block and decrease the weight of the car.
Thank you for posting these videos, I don't know much about cars but I am in love with jap cars myself. These video's are slowly helping me learn more about my car and I hope to be able to work on my car at a proffesional level so I can fix any problem and tinker without worry ;). I just don't know where to start :( haha but this is a good start getting to know everything first so thanks!
Sir:
You are very generous to explain these concepts for everyone to understand, I really feel grateful to you. One tiny question; How do you increase the internal pressure on the cylinder? And what does it have to do with the CR? Are Honda's engines (for ex the F20C, K20A)greater in this sense than others? Thank you in advance!!
Still found this super useful in 2020.
Use the fuel that your car manufacturer recommends. Cooler air is more dense, yes, so everything else being equal, cooler air will have more O2. This isn't necessarily the case at higher elevations.
Change the engine geometry. New internals, domed pistons. It's not usually as simple as changing one thing, you'll have to have a group of components that work together including the crank, rods, pistons, cylinder head, and valves.
I swear, i come to your channel almost daily to watch at least two vids...some i've watched 4-5 times already...don't know a great deal about cars, just basics.
Refer away, I'm always looking for new material to learn from. As far as CR dictating efficiency, my source isn't wiki; that's just an easy one to check, which MOST of the time has accurate information. But if you'd like the source, it's the last book that I've referenced on the FAQ page of my website (see description) titled "Engineering Fundamentals of the Internal Combustion Engine."
Finally the explanation I was looking for
You might have mentioned that when the piston is at BDC and ready to initiate the Compression Stroke, that the intake valve (and obviously, the exhaust valve) are closed.
I'm always interested to use Premium fuel. After watching this video, now I know where to use such fuel. Thank you !
It's the distance from the top of the piston (assuming it's flat) to the top of the cylinder head when the piston is at its lowest point, divided by the distance when the piston is at it's highest point.
Once again, this would assume the piston and cylinder head are flat, which they are not. So really you need to measure the volumes at BDC and TDC and divide.
This is throw back as hell bit I still learned something today
You've come along way my man
The current compression ratio of your vehicle, yes. If you haven't altered your engine at all, yes, the stock compression ratio. Should be available online or in a user manual.
Humble beginnings!
@IronPump89 Diesel engines have higher compression ratios because they use the heat from compression to ignite the fuel. Gas engines use a spark to ignite the fuel, so lower compression ratios are used; otherwise the fuel would ignite at an undesirable time. Yes, direct injection on gasoline exists and is now common, but a spark plug is still used to ignite the gas so lower compression ratios are still used. Though Mazda has incredibly achieved 14:1 in the Skyactiv engine for the Mazda3. Kudos.
Best explanation I've heard in years
Increase the CR to increase the pressure. High CR ratios are typically more efficient than lower CR engines.
For YEARS i never knew what this meant and i'm a damn car nut - thank you!
had to do a presentation on this but it seems like nobody knew how to explain it to me thank you!!
Yes, increasing the stroke would be a way to increase the compression ratio, which of course alters the geometry of the crank/connecting rods.
Yep, I need to look into this more, it's pretty interesting.
I love it how you activelly reply to comments on your videos. Good Job!
*Gone in 60 seconds*
3:00 minute video which is great, but you explained it in the first 60 seconds.
Thanks.
No, it depends on the design geometry of the engine. But you'll typically use higher octane fuels with higher compression ratios.
you explained better in the first 50 seconds what it means than anyone ever has in my life 😂
Thermal efficiency, theoretically, is determined by compression ratio. Not sure what the equation is, but the theoretical thermal efficiency goes up as compression ratio goes up.
I love the way he explains compression ratio. Do you have any more engine videos?
pekis
This is a whole lot simpler than I thought it was
Please keep making these videos!!! Me and my buddies love them. We are big gear heads and this is the easiest way to learn about engines Thanks!!!
Very good explanation, thank you very much.
Awesome, good luck to you!
Well direct injection seems to help a lot with compression ratios. In the US the Mazda3's skyactiv engine has a 13:1 compression ratio, capable of using regular octane gasoline. In the rest of the world it has a 14:1 CR and uses premium. Not totally sure how they do it but I know direct injection plays a good role. Also, the R35 probably has a lot more boost than the 1.4 TSI, so a it's logical that a lower CR would be used. Could be wrong on that though.
Lol, so your telling me a 426 Hemi with 13 to 1 compression gets pretty good mileage? At least according to compression ratio?
Love the vids man. I really learn a lot! One thing... Hit and Miss? I know how they work, but not sure if you or any of your other subs know how they work. If you don't already have a vid explaining, well here is a recommendation. Hit and miss is really interesting on how they work, and I'm sure people would enjoy a video explaining how they work from you.
No Sindbad. 8/1 is the volume ratio. Say 8 = V1 (volume at bottom dead center) and 1 = V2 (at Top dead center in simple terms piston pushed all the way up) this means the volume of the cylinder was compressed or made small from size 8 to size one.
Think of a syringe filled with water lets say. If the top part is sealed (n opening). What do you think will happen when you try to push the syringe plunger up ? Higher pressure because you are compressing the water inside.
THANK YOU always finding my way back to this channel! SUBSCRIBED
perfect mate. I am not thick. I just couldn't visualise what was meant. What the relationship actually was. so you explained that perfectly in the first sentence.
Thanks
Mostly from a higher compression ratio. Longer stroke as well.
Watching in 2021 bro. Watched sinced the beginning. Happy for u man
mechanical engg?? nice actually i'm studying mechanical engg and your videos help me a lot to study about cars so thank you veryy much:-)))
Are you a teacher yet? You're better at this than my materials professor. Thanks, man.
I have not heard much about relationships between compression ratios and turbo lag.
Maybe.
I suppose it depends on how you increase the stroke. If the stroke increases in length (closer to the crank) and has a larger gap at TDC, then I suppose a lower compression ratio could result. Haven't read up on it or anything though.
The engine is more efficient with high CR, so even though more power is produced, it doesn't necessarily mean more fuel is used. Higher CR means better fuel economy over a similar engine with a lower CR.
Wow !!! absolutely brilliant explanation...thanks for the video...you have no idea how beneficial this is for me...keep it up mate !!!
Wow it's been so long dude!
Thank you. You explained this very well. It is so easy to understand 😊
Just helped me pass a mechanics quiz
Thanks dude
Great job explaining it. Made it real simple to understand.
Great to hear!
I like your videos dude. Keep up the good work because of you I'm learning about the stuff I love
Two CRs are important here, geometric and effective. You can have different CR and ER geometric values, look at the Gomecsys crank for a geometric difference, or even the true Atkinson cycle (not what Toyota claim they have). Ways of achieving different dynamic CR and ER are possible with variable valve timing (psuedo-Miller cycle). Late intake valve closing means you get a low CR, but a normal exhaust valve opening means you have the geometric expansion ratio. Did you get my PM?
Thanks!
Impressive to see this video where you started
thank you for this video.. now i understand more about CR and the engine knocking... and why mazda is campaigning so much about their new Skyactiv engine which has 14:1 CR..
You, my friend, explain like a boss
@mk91077 Yes, that engine is absolutely insane. And in the states it has a CR of 13:1, with 87 octane fuel. Absolutely phenomenal engineering. Watch my video on octane ratings if you're interested.
Depends on the aspiration, but from an engineering POV the higher CR engine will typically be more efficient, so that's what I'd go with.
Assuming the 10:1 is more efficient than the 9:1, and it's essentially the same engine, with altered compression, then yes, it could be more powerful. But you can't simply use CR to compare engines' power.
Wow just happen to stumble upon an awesome channel. Thanks for making such great content
Okay, I get what you're trying to say. But point is, higher expansion ratios are not possible without higher compression ratios. Surely, a car with a low CR can have a better expansion ratio than a car with a higher CR, but realistically speaking, there is a relationship, is there not?
Thank you for a very thorough and easily-understood explanation.
I did indeed, thanks for the info.
Could you make a vídeo explaining the effects of camshaft duration and forced induction in dynamic compression ratio. It is allways tricky for people modifying their engines with longer duration cams and turbo to figure out correct cr and dcr. Thanks
This is the first time I understood why CR=8.1
Thanks.
Brilliant. Clear and concise the way I greatly hope a most astute human mind could fundamentally understand engineering as a human endeavor, necessarily being capable of making the detailed knowledge practical to the layman.
Nicely presented, thanks.
Only if your car requires it, use whatever the manual says to use, as that is what the engine was designed for. Going higher than necessary typically will not provide any benefit.