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.
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!
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.
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.
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.
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.
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.
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.
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.
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!!
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.
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.
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.
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!
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.
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.
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.
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 was just trying to figure out what the average 2 cycle engine has as far as compression ratio and whether it makes sense for premix fuels to use 91 or 93 octane or not. Nice explanation of CR. Thanks
not sure if you're still reading comments from old videos, but what happens when you put low octane gas in an engine that is made for high octane gas? If I understand your lesson correctly, that means the fuel will combust before reaching the ideal compression ratio because the lower octane gas cannot withstand the temperature of the high compression. So does it mean it will combust before the spark plug even "gives the spark"? Will it then cause a timing issue on the engine/drivetrain?
Hey man, I have watched a bunch of your videos I really enjoy the way you simplify complex ideas. When you see 3 numbers in a ratio like; 9:0:1 what is the third number for? Also can you please elaborate on why the engine knocks because of the compression, what physically causes the engine to knock? I watched your video on knocking just not sure what makes the "ping" sound. Thank you again for your videos and explanations. Have a Great day.
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.
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.
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.
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?
@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.
Hey EngineeringExplained, can you explain what liters are when talking about engine size? For example, I've heard that a 2.0 L engine means that it produces 2,000 cc of displacement, but I've also heard that 2.0 L refers to the maximum amount of gas and air mixture that all the pistons can hold combined (2.0 liters of mixture). Can you explain what liters truly mean when talking about engine size?
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."
I don't know if you're still checking the comments on such an old video, but why would the compression test results be significantly higher than manufacturer specs? The car in question is an old aircooled VW 411, with an unknown capacity replacement engine. The workshop manual states 114-142psi (100 psi wear limit), but an actual test done today showed 165 psi on 3 cylinders, and 180 on the other one (that cylinder was also dead some time ago, due to a fouled plug). I'm already using Techron-laced fuel, and the plugs were all clean, so I don't think it's due to carbon buildup.
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
Nice and simple explanation, thank you. Was wondering what the third number represents as I often see drag race tuners mention three numbers instead of two. Cheers mate:)
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?
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.
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.
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..
Can you explain the relationship between compression ratio and turbo lag. I think i've read that the higher the compression ratio, the lower the lag. is this because high comp engines have a higher piston travel and hence are able to spool a turbo quicker?
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.
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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 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.
Very welcome, glad you find the channel useful!
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!
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!
googled engine compression explained and this vid came up first, awesome. keep making more good vids
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.
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 😭
Helpful, short, straight to the point.
Man you have come SO FAR since this video. Congrats on making it man.... I love your videos they’ve helped me on occasion.
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...
Your videos are amazing and you explain everything from simple to complex in digestive chunks. Keep it up, and thank you.
I love you, you're the cheat sheet to my life.
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.
Man you have done it again!! ive learned why premium fuel is important and what "knocking" is. and the reason for compression ratios.
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.
Came here from ur new video, about VCR engines !! Totaly worth it !!
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.
Certainly, but it will take me some time. Traveling now, starting work soon, and tons of requests to fulfill! But I'll get there!
Really excellent video. Simple and to the point without telling us a long story or screaming into the camera.
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.
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.
Great to hear, that's why I made these!
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!
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.
Humble beginnings!
Finally the explanation I was looking for
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!!
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 it how you activelly reply to comments on your videos. Good Job!
I love the way he explains compression ratio. Do you have any more engine videos?
pekis
Still found this super useful in 2020.
Maybe.
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.
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!!!
Correct, to prevent pre-detonation from occurring since the air/fuel mixture will reach higher temps with higher pressures.
You've come along way my man
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
Best explanation I've heard in years
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!
Very good explanation, thank you very much.
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.
This is throw back as hell bit I still learned something today
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.
This is a whole lot simpler than I thought it was
Correct, except for frictional losses of course. I do have a video on cylinder-deactivation as well for anyone who's interested.
@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.
I'm always interested to use Premium fuel. After watching this video, now I know where to use such fuel. Thank you !
THANK YOU always finding my way back to this channel! SUBSCRIBED
had to do a presentation on this but it seems like nobody knew how to explain it to me thank you!!
For YEARS i never knew what this meant and i'm a damn car nut - thank you!
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.
Watching in 2021 bro. Watched sinced the beginning. Happy for u man
Nicely presented, thanks.
Are you a teacher yet? You're better at this than my materials professor. Thanks, man.
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.
Brilliant explanation for beginners like me, thank you. Does some firearms also work based on this principle?
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.
Wow !!! absolutely brilliant explanation...thanks for the video...you have no idea how beneficial this is for me...keep it up mate !!!
I was just trying to figure out what the average 2 cycle engine has as far as compression ratio and whether it makes sense for premix fuels to use 91 or 93 octane or not.
Nice explanation of CR. Thanks
this is for my exam tomorrow, what is the relationship between engine efficiency and compression ratio? any points will help
not sure if you're still reading comments from old videos, but what happens when you put low octane gas in an engine that is made for high octane gas? If I understand your lesson correctly, that means the fuel will combust before reaching the ideal compression ratio because the lower octane gas cannot withstand the temperature of the high compression. So does it mean it will combust before the spark plug even "gives the spark"? Will it then cause a timing issue on the engine/drivetrain?
you explained better in the first 50 seconds what it means than anyone ever has in my life 😂
Hey man, I have watched a bunch of your videos I really enjoy the way you simplify complex ideas. When you see 3 numbers in a ratio like; 9:0:1 what is the third number for? Also can you please elaborate on why the engine knocks because of the compression, what physically causes the engine to knock? I watched your video on knocking just not sure what makes the "ping" sound. Thank you again for your videos and explanations. Have a Great day.
You, my friend, explain like a boss
Wow it's been so long dude!
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.
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.
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 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?
I have not heard much about relationships between compression ratios and turbo lag.
@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.
Hey EngineeringExplained, can you explain what liters are when talking about engine size? For example, I've heard that a 2.0 L engine means that it produces 2,000 cc of displacement, but I've also heard that 2.0 L refers to the maximum amount of gas and air mixture that all the pistons can hold combined (2.0 liters of mixture). Can you explain what liters truly mean when talking about engine size?
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."
Great job explaining it. Made it real simple to understand.
Great to hear!
I don't know if you're still checking the comments on such an old video, but why would the compression test results be significantly higher than manufacturer specs? The car in question is an old aircooled VW 411, with an unknown capacity replacement engine. The workshop manual states 114-142psi (100 psi wear limit), but an actual test done today showed 165 psi on 3 cylinders, and 180 on the other one (that cylinder was also dead some time ago, due to a fouled plug). I'm already using Techron-laced fuel, and the plugs were all clean, so I don't think it's due to carbon buildup.
Yep, I need to look into this more, it's pretty interesting.
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
Increase the CR to increase the pressure. High CR ratios are typically more efficient than lower CR engines.
No, it depends on the design geometry of the engine. But you'll typically use higher octane fuels with higher compression ratios.
Mostly from a higher compression ratio. Longer stroke as well.
Thank you for a very thorough and easily-understood explanation.
Wow just happen to stumble upon an awesome channel. Thanks for making such great content
Impressive to see this video where you started
Nice and simple explanation, thank you. Was wondering what the third number represents as I often see drag race tuners mention three numbers instead of two. Cheers mate:)
Just helped me pass a mechanics quiz
Thanks dude
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?
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.
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.
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..
Can you explain the relationship between compression ratio and turbo lag. I think i've read that the higher the compression ratio, the lower the lag. is this because high comp engines have a higher piston travel and hence are able to spool a turbo quicker?
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
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:-)))
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.
Thanks!
Very good video man! You are very good at making me visualize all of this. Thank you!
You are a very excellent teacher.