Compression Ratio and Thermal Efficiency

[@EngineeringExplained]

That's the idea, learn it all! :) Ask questions along the way.

[@EngineeringExplained]

Apologies for the unclear voice. Let me know if you have any questions.

[@EngineeringExplained]

Yep. Reducing rotational inertia is one way, which I'll discuss in the next video. Also, if you can turn more of the heat into useful work. Any reduction in friction.

[@EngineeringExplained]

I believe it ultimately comes down to the temperature difference (before and after combustion) which is larger with higher compression ratios, as well as the expansion ratio (opposite of compression ratio).

[@gsilva220]

So basically, until you reach diminishing returns, the more you increase the temperature of the air-fuel mixture without getting knock/autoignition, the better? Would this explain the higher efficiency of diesel engines, in which fuel is injected _well above_ autoignition temperature?

[@Joeldc510R]

Can you make a video explaining volumetric efficiency?

[@EngineeringExplained]

Typically it's not something you'd change, but you can do so with different pistons, or different connecting rod geometry.

[@EngineeringExplained]

Basically higher boost engines may use lower CR because the boost will give them added pressure/heat, and higher compression ratios would require better internals to handle the additional added pressure.

[@EngineeringExplained]

The essence is, a higher compression ratio allows for you to theoretically use more of the heat your engine produces and turn this into mechanical work, than a lower compression ratio.

[@donchiller666]

Btw this is one of the most informative engineering channels I came across so far. :D Thank you

[@EngineeringExplained]

Yes, to the first question; diesels are more efficient. You can search my channel for the video "gasoline vs diesel."

[@bax442]

Engineering Explained we need a video about relationship of: Octane Rating vs Compression Ratio vs Ignition timing. (knocking) Could you make a video about it, everyone on the internet says different things. Very little letters and materials about it at all. With an example such as: An engine currently runs on 95 octane (European rating), how can CR and Ignition Timing be adjusted to get a benefit from switching to 100 octane (European rating) or equivalent. What is the max CR for certain octane rating? Thank you for all of your videos. Please let us know if you could, it seems very complex and complicated. Guys, thumbs up for the video.

[@GodGritGains]

bax442 he does a video discussing this. I believe it’s in the video where he talks about the differences in octane rating and knock.

[@787brx8]

I can advance ignition timing to the maximum factory setting possible without any knock. I made A short video on the subject.

[@manishmishra6613]

787brx8 can you please share a link for that...it will be good for us to know

[@karlwalker1771]

I know this video is over 4yrs old but after trying to study/comprehend this video explanation, could "YOU" or one of your viewers please explain this in a simple/ layman's terms as the equation is all fine and dandy for some but a simple explanation or anecdote of an answer would be very much appreciated :) PS, I want to basically know if a HONDA FIRESTORM 1000F ENGINE tuned or intended to run at 9.4:1 is good or bad and what engineering procedure would you use to perfect this engine? I would like to skim the head as this always gives ANY engine a boost. Any qualified or sensible answer/advise would be greatly accepted and spread on the VTR forums! Thank you, young man, for your science behind the 100-year-old combustion engine formula and I say this with as much passion as you have shown in your anatomical explanations, well done, sir :)

[@EngineeringExplained]

I hope so, if not I'd be glad to teach him.

[@EngineeringExplained]

Piston shape, rod length, cylinder heads; this of course means redesigning the geometry of the crank/connecting rods. It's not really something you do after the fact, more of when you're designing an engine from the ground up.

[@jimi2guns265]

Can compression ratio be controlled by timing . Shorter center lines or variable timing ?

[@arckon09]

This would have been a good opportunity to introduce the concept of dieseling, another great video none the less! Keep them coming!

[@EngineeringExplained]

Mazda's SkyActiv is 14:1, on high octane gasoline. On lower octane I believe it is still between 12 and 13:1.

[@xXJeReMiAhXx99]

turbos or any forced induction could do the same thing, it wouldn't alter the compression ratio of course but if it was forcing twice as much air into the cylinder to begin with than a 10-1 turns into 20-1 and comes with all the same perks, more efficient, bigger harder to contain bang and risk of engine knock.

[@EngineeringExplained]

I have a hybrid/electric playlist in the works, I could certainly add on hydrogen.

[@mrscrewu1199]

I 3D printed an environmentally friendly engine in PLA and in running renewable ethanol fuel with a compression ratio of 600:1. Keep up.

[@donchiller666]

Excellent video, you did a better job of explaining than all of my teachers. ^^

[@FreakinKatGaming]

like to start off with how thankful I am of your videos, you have taken many years of your life into learning the exact nature, mechanics and over all simplifying it all so I don't hafto :D now that's a RL high CR and knowledge gain if Ive ever seen one. Ok back to my question and curiosity, how could and or what could be done to overall increase the reduction of increasing negative temperatures? what I want to envision (simplified) is a new more efferent way to get rid of the built up heats around and in the compression chambers and at the same time because I believe it would be better to and a little more rational to instead of trying to find a place to vent the excess heat away from, vent it in sequence to decrease the minimum fuel burn (yes its in extremely low low low numbers) to cause combustion in a sense the longer the vehicles running Normally power is lost and the engine loses its peak from that point on, but if you can reuse and expel excess heat the car would maintain a longer peak and steady race where as the other vehicles would be suffering from. basically put turn a weakness into a strength. I know what id like in reality sense isn't going to happen out of the blue but if it was given a considerate amount of thought and effort with the right minds, if that car was in a race it should be clear that its power can be maintained a lot longer then its competition.

[@Kaydess]

Damn I wish I had known about your channel earlier, I have to watch each one of your vids to be sure to understand every bit of your new videos. Keep up the good work, I love it.

[@EngineeringExplained]

Sure it will; it gets the job done certainly but it's not very efficient, and will likely be phased out over time. Maybe not in our lifetime, but relatively soon. Diesels are superior from an efficiency standpoint; it's unfortunate they're not too popular in America.

[@EngineeringExplained]

Because this is the ideal equation, meaning if the engine turned all heat into work it would operate at an efficiency of what was shown. In reality engines lose a ton of energy through heat.

[@EngineeringExplained]

No, the high temperatures of the compressed gas is enough to ignite the fuel once it is injected.

[@EngineeringExplained]

It's not quite that simple. The higher compression ratio would mean you could create the same amount of power of an alternative engine (all things equal but with a lower CR) but at a lower RPM, thus using less air and less fuel overall.

[@EngineeringExplained]

Theoretically, yes. Because you're producing the power you need to accelerate with less fuel than if the engine had a lower thermal efficiency.

[@sportsmansparadice42]

Are you saying that the Mazda Sky active engine is 60% efficiency? That's kind of hard to believe. Mercedes Benz Engineers have an F1 engine that is 50% efficiency.

[@EngineeringExplained]

SkyActiv is not 60%. Peak is around 43% I believe.

[@sportsmansparadice42]

@@EngineeringExplained Even at 43% that's pretty impressive.

[@EngineeringExplained]

Correct, IC engines are not efficient at all. Electric will definitely become more prevalent. Tesla is pioneering the infrastructure as we speak. It's cool to think about.

[@C.J.M]

Funny how I did a final year project on this and just submitted about two weeks ago and bam, you make a video on it lol. Good video though.

[@Tomutho]

Very good video, at first I thought it wass very difficult to understand, but now I get the idea.

[@EngineeringExplained]

Thanks!

[@EngineeringExplained]

Interesting, I remember building an engine in high school and that was its CR.

[@smolbabyxx]

Can i just say i had a class test that takes up 20% of my gpa AND UR VIDS SAVE MY LIFE NO JOKE😂😂😂😭😭😭❤️

[@Davidtiff]

Hey Man. Very nice explanation for a newb like me. Thank you for the mathematical explanation prior to the compression ratio discussion, it made much more sense.

[@creedence1819]

Could you do a video on the ratio of specific heats?

[@SavageJim01]

I am subscribing! You give great summary lectures, even though they are not extensive as a thermodynamics class, you hit all the important points and explain the reasons why they are important wonderfully. Just a suggestion on another vid you can do to follow up this one: go over the factors that rob the system of this ideal efficiency return such as heat loss, materials strain absorbing energy, the surrounding materials absorbing heat, trapped CR vs geometric CR, exhaust gas temps,sound,etc.

[@KillerZero259]

i had to pause the video at 4:27 to say this: EngineeringExplained, PLEASE, PLEASE, PLEEAASSEEE do a series on thermodynamics!!!!

[@EngineeringExplained]

Yes, assuming the gas tank is the same size.

[@EngineeringExplained]

I wouldn't assume there's anything wrong with it for the winter. You don't need 100 kW just to drive in the snow.

[@leonidassaber7335]

Can you talk about ipm motors and why they are so efficient?

[@ArvinRedlineexpress]

thanks for your thoughtful and informative video. As a gear head i routinely come across all sorts of ratios but i couldn't comprehend their significance and the relevance to efficiency. I ran the numbers for my car and now i have one more thing to brag about =) jk

[@tomterahedrob]

Do you think its a good idea to coat the piston heads and insides of cylinder heads with ceramic coatings to resist heat and heat transfer to cooling in order to gain more power, fuel efficiency and longer engine life?Ceramic engines a possibility in the future?

[@jakegrimsrud7448]

@Engineering Explained In step 3 you stated that the thermal efficiency is equal to 1 - ((T4 - T1) / (T3 - T2)). This equation was originally: 1 - (Cv(T4 - T1) / Cv(T3-T2)). I'm assuming you just cancelled the Cv's on top and bottom to get the equation written on your whiteboard. Is that right?

[@nadzirahmuhsin6863]

What is CV?

[@luisgordillo1695]

On newer engines that have cylinder deactivation ,that thermal energy at the end of the combustion stroke doesn't leave through the exhaust valve anymore. when the cylinders deactivate the Inert gas gets trapped inside and causes a spring effect on those off pistons,! this helps with a smooth transition from all cylinders to the cut cylinders.

[@EngineeringExplained]

I do have a video on Octane ratings, do a quick search on my channel page. :)

[@BasedBidoof]

This helped me understand a lot more, thank you

[@samrattomar7552]

Very good my friend....I really appreciate your knowledge and sence of narration....keep it up..!!!

[@Recogru]

Ford along with another company helped create PWTA cylinder walls or Plasma transferred wire arc thermal spraying. Crazy sounding stuff and I think either Ford or Nissan own the rights to it. It completely eliminates having cast iron liners in an aluminum block thus saving weight and reducing friction from what I understand.

[@eduardwalhout1740]

Excellent lenght for a small nap. Thanks.

[@fraxonthefurry21]

Have you explained water/methanol injection? Thats probably a good one to add to the list.

[@bdigvijay]

Hello Sir, can you please explain what is dynamic compression ratio and how does it affect engine efficiency ?

[@hamdanalharbi2206]

how does boost affect compression ratio and thermal efficiency ?

[@treyz28]

It doesn't effect compression ratio. It's mechanically set

[@Tore_Lund]

@@treyz28 But cylinder pressure goes up, so it has the same effect = more power and higher efficiency, both because of higher pressures and because some of the energy wasted in the exhaust, gets reclaimed by the turbo. So it is like a higher compression engine, where the engine gets some help to compress the charge.

[@nicolastremblay7527]

​@@Tore_Lund The pressure goes up, but still the volume before and after is still the same. Even if you put more air in it, it will still compress that air in a ratio of 1:14 in the exemple of skyactiv engines. The big upside of an turbo for efficiency is the weight. Turbo setup doesn't weight that much compared to building an engine powerful enough to compensate that power. Less weight = goes faster. And its smaller too.

[@Tore_Lund]

@@nicolastremblay7527 -Which is exactly what I said; It is "like" higher compression ratio, but better because the extra volume is compressed by energy otherwise wasted. I could have written it more clearly! Cheers.

[@smh9902]

@@treyz28 Thats actually not entirely true. There is static compression ratio and dynamic compression ratio. Dynamic is all that matters, but because its so difficult to calculate at any given RPM and atmospheric condition most people use static because thats the mechanically set CR. The dynamic CR is affected by RPM, scavening ratio, volumetric efficiency, atmospheric conditions, etc.

[@GOD12A]

I'm curious to the relationship between compression ratio and boost (forced induction). Years ago engine builders were building low compression/high boost packages, but recently there's been a shift towards higher compression/lower boost packages. If the combustion pressures are the same (at a given rpm), what other differences may be seen other than intake temp on the high boost package and increased lag in the low boost package?

[@Iflyagrasshopper]

High compression creates heat which when squeezed into a small space tends to be absorbed by engine components. It also creates a lot of frictional losses. Mazda Lowered the compression yet improved the efficiency of it's diesel engine. Sky Active D is using valve timing to lower the effective CR yet maintains a high expansion ratio. Toyota recently achieved a 37% efficiency with a 9:1 compression Atkinson engine... Also Honda has achieved high efficiency with it's EX link engine. Why not talk about expansion ratios which are the real key to increasing an engines efficiency?

[@guillaumegaudin694]

+John Lucas actually the mazda skyactiv diesel reduce the CR so to reduce the heat in the chamber when burning lean, allowing a reduction of NOx production.

[@Iflyagrasshopper]

Yes, Maybe my comments were confusing but that's the point I was trying to make... low compression but high expansion...

[@barath4545]

Loved this video and waited for it, to check if I was wrong in my perception of it. Wasn't far off, that is, now hoping your'e right :) Thx again, btw you should mention the racing engines that run N/A only classes: F1 has a 17:1 CR last time I checked and Nascar is 12:1. Will you do a video on the octane rating soon and how fuels prevent knocking and how this relates to the CR? (Sorry if you did already and I missed it)

[@mahendradhepe7277]

Video on camparison of si and ci on the basis of Thermal efficiency Fuel consumption Operating variables Distribution of fuel Performance characteristics

[@UltraGamer77]

A video about how the steering works would be nice :)

[@alejandrotrabucco1827]

hello, you could make a video detailing the different configurations of the turbo engines, advantages and disadvantages. for example: 300hp engine. what if happens the engine have 12 -1 comprecion and 12 psi or another config 7-1 comprecion and 40 psi. Both are going to have 300hp

[@arghyakamolroy7760]

Actually, you have shown the relationship between fuel conversion efficiency with Compression Ratio(CR) and not thermal efficiency. To make Thermal efficiency and CR related, we need to consider combustion efficiency equals to unity. So please mention it if possible.

[@EngineeringExplained]

Yep, last Wednesday.

[@lanleg]

Hi, Impressive training !! I love. Little question from Paris - France.. Could you possibly explain how efficiency is increase in GDI's engines. Why does direct injection permit to increase the CR ? Thanks

[@johnnybanks61]

The internal combustion engine will never die. I just think we will move to more efficient fuels and engine technology. Are any companies using ceramic coatings in the cylinder walls? Or why don't we move to diesel as the preferred fuel for vehicles? I should really post some videos on the engineering feats in my ford powerstroke. My diesel will rev out to 5000 rpm and provides adequate fuel economy.

[@rgvakis]

very nice vid! could you make a video about what is cylinder head squish band? and how it affects horsepower?

[@robertdupond2154]

@Engineering Explained What does the K represent in the sheet you gave me?Also , what are you trying to prove on the graph.I understand if the compression ratios is 14:1 you get 60.29% of thermal efficiency . but red line(C) why 65.20 % . Why a blue and red relation why not just the blue one?

[@EngineeringExplained]

Interesting, right now I think it kinda looks like a stick shift pattern.

[@leonofdragonstone1250]

So, in theory, a high efficiency is an engine that uses hard to ignite fuel a high compression ratio? so we are limited by the physical properties the engine is made of, as well as how tight the relationship of the piston and cylinder is...

[@warrensmith410]

Wonderful video! Question: "K is a ratio of specific heats." Specific heats of *what*? (I am guessing air and the fuel -- am I right?)

[@robertdupond2154]

@Engineering Explained Can you please com up with a video that shows how to get from 1-(T4-T1/T3-T2) to 1- 1/(cr)k-1?Can you give us a better understanding of thermodynamics.

[@EngineeringExplained]

The reason I did not is that it's fairly complex, and requires and understanding of many parts of thermo. I included a link to the derivation in the video description if you are interested, but it really isn't something that can easily be summed up in a few minutes.

[@LBB988]

Can u discuss the relation between the boost and CR,why lower CR at high boost and some keep it the same with forged internals, what's the difference between destroke and lower CR thanx.

[@tomterahedrob]

David Blume says in Brazil VW stopped making gasoline cars Now theyre ethanol only.He says they have cars with 12.5 to 15.5 to1 compression ratios and even though ethanol os 63-65% the heat value of gasoline they get same or slightly better fuel economy on ethanol.Heres what I want to do:I want to convert my 6.5HP gas engine (8.5 comp ratio) into a15.5 to1 comp ratio 100% ethanol only engine.How would I do that?Change the crank shaft? Thanks!

[@pratyushbhattacharya9527]

am a fan of urs!!doing a great job!!but hv a question.....thn CI engs r more powerful than SI as their CR is greater.therefore cars having CI eng shld be faster than SI eng cars as more HP means greater acceleration..but why do i feel that the lower end acceleration of petrol cars>diesel cars?

[@rickitickidicki]

Have you done a video comparing/contrasting diesel vs. gasoline engines? Which is more economically efficient? How long does a 50mpg diesel engine last? Is it turbo? Boost? What does the diminishing returns look like for supercharged gasoline engines as far as mpg goes. I know that's a crippity crap load a questions, so please feel free to brush them off or take as much time as you wish...I know you got a life outside tha tube.

[@alexanderjacobs7799]

So, if the Mazda engine can theoretically produce 6% more power, how does that relate to fuel efficiency? Are you saying because the thermal efficiency is higher that fuel efficiency and power will both increase?

[@kenterprise1]

Nice. For carbon based fuels this equations explain the ineficiency of engines. "Energy" is stored in a chemical form then is converted in a thermal form then in kinetic form. To improve efficiency the conversion phases should be reversed. The chemical stored energy is converted into kinetic form and losses are thermal. Engines are poor thermal machines but excelent pressure converters. This make explosives better "fuels" than gasoline. In fact are used to start some engines. But storage rise bigger problems and manipulation is dangerous also. What if a chemical compound like ammonia nitrate is detonated by spark plug ? How those equations will be written? What other implications ( other that oil industry restructuration) may have conversion of actual engines on this chemistry instead of carbon oxidation ? What if most of this "fuel" may be produced onboard in a super efficient close loop? I think that this was done and labeled " water car", called impossible and rejected because not fit in the theoretical 60% and practically no more than 20% efficiency of actual vehicles in a age of space exploration.

[@AndyRRR0791]

+Marius Moldoveanu thermodynamics is applicable to anything related to heat. It doesn't dictate carbon-based fuels. In fact, you can even have solar-powered heat engines.

[@sadsismint]

I think i'll have to watch this one again and pay more attention. I didnt get it so much the first time around.

[@shanejones809]

What's the CR at which the relationship between CR and efficiency begin to level off?

[@palmerjames29]

And you can change the curve if you change the type fuel a diesel and the direct injection can help with knock if you inject it at the right time

[@zeeqco]

Hello there... im here have a request for video... I have Ford fiesta 2012 with 6 speed dual clutch gearbox... I need you to explain how to reduce it n what electronical parts that controls the clutch... just so you know that lately my car sometimes make some noise when transmission... but when I send to service they told me that they have to update the software to make it less noise... but i dont feel it reduce the noise... please make a video what is going on with this dual clutch type

[@AliSalman]

I am going to build a new hellcat 6.2 litter with high boost what is the powerfully Compression Ratio ? I need advice

[@michaelstoltz58]

I thought the ECM controlled the AF mixture to keep it at Stoic pressure. Which would also control the burn. Also heat is a killer. Now were talking performance vs longevity.

[@bax442]

Please replay, are You talking about static or dynamic compression ratio?

[@konforzone]

hey. could you explain effective compression ratio in forced induction engines.

[@soundseeker63]

Although he didn't actually say it, this partially explains why diesels are more fuel efficient. The other factor of course being the higher specific energy of diesel fuel.

[@diotough]

Ehm, I might be wrong about it, but I always thought the correct firing order is: 1-3-4-2. If 3 just fired then 3 is in power stroke and 1 can not be in a compression stroke. 4 is about to enter compression while 1 is about to expel the burnt fuel-air-mixture. Your arrows are a bit misleading as 1 and 4 move in the same direction.

[@EngineeringExplained]

+diotough You're reading into this a bit much. The illustration is the various steps of a single cylinder firing. Never said it was a 4 cyl.

[@diotough]

+Engineering Explained Ok, but I think in that case it's at least misleading. You basically have 2x the compression stroke but no intake stroke and 2x the power stroke but no exhaust stroke. Or are you just trying to illustrate the times at which (hypothetically) the measurements are being made? I had to watch it 3 times until that interpretation of the illustration came to my mind. Don't get me wrong: the message and the facts are correct, it's just about the illustration. Your channel is great and very informative even for people who know a lot about the mechanics and principles.

[@EngineeringExplained]

+diotough T1 = Piston is about to start compressing. T2 = Piston has completed compression. T3 = Spark ignites mixture, peak temp/pressure. T4 = Exhaust stroke, piston reaches BDC.

[@diotough]

+Engineering Explained Yes, that was my second assumption. I had to watch it three times in order to understand it. It would be clearer if you'd have used captions. At first I thought of a 4 cylinder engine and after that of the 4 different strokes (Intake, Compression, Power, Exhaust). That's what confused me. Still: the last arrow needs to point upwards in order for T4 being Exhaust stroke. ;) Again, great channel and great work of yours.

[@JomanSofly]

+diotough it was clear to me .. i just don't get what are you trying to say ;S

[@sammyhtb]

so can the manufacturers increase compression ratio and decrease amount of fuel in air fuel mixture to get better mpg? Please confirm. love your vids

[@palmerjames29]

Could you/ or did you explain the thermal dinamics...... And I'm sure may or may not know this but the engine you're talking about with high compression "40/1" is a diesel... You should make a video on that for other people highly recommend a diesel super efficient vws

[@olipirard]

Hello 3E, Does a 14:1 combustion ratio would create a self fluel mixture ignition? If not can you tell me what would be the limit? Thanks.

[@EngineeringExplained]

Ferrari and Mazda have managed a 14:1 CR I believe.

[@goforthlp]

Engineering Explained Are you an Engineer, and if so where did you do to college?

[@ptmww3]

HI man, Can you please tell me how is a pressure cap tested for correst operation? thanks

[@bubster1981]

Can i take a direct psi reading from an engine and get a ratio? Like would a psi reading of 180psi be roughly 12';1 ?? 12 x 14,7.....if the limit is 11;1 on pump fuel what in the world is that same limit in psi??

[@PJWALL89]

my car has 13.5 compression ratio. Dose this meant i need to use higher octine?

[@K_Sadek]

b-but if all the heat is transferred to Work then the efficiency would be 100% right? I think that both equations won't yield the same result.

[@acelakid94]

Please do a future video about cars that can run on hydrogen. Like the BMW Hydrogen 7.

[@Vennillion]

Hi, I don't know if you heard about the new 5000hp Devel Sixteen Supercar, but anyway, is it possible for a normal gasoline engine to sustain all that power? And if yes, is it possible to sustain all the heat the engine is producing (more than 10000kW!) ? Thank you.

[@ΑΡΗΣΚΟΡΝΑΡΑΚΗΣ]

if you take an diesel engine and modify it to burn petrol...

[@jeff77789]

how about rotary engines?? im pretty sure rotaries are not efficient because the angle that the expanding air pushes the rotor is not very efficient, resulting in a lower thermal efficiency

[@LBB988]

thanx, can u tell me what's destroke is it = to lower CR

[@INCC74656I]

my engines factory ratio is 17.2:1 and i was thinking of boring it to increase the ratio, now i know i need to figure out where my diminishing returns makes it pointless to add the extra stress to the engine...

[@EngineeringExplained]

Bad timing on my part huh? Sorry man!

[@rickitickidicki]

thank you for responding so promptly, eventhough i just got rickrolled