Comments by "H. " (@LocPH.) on "Engineering Explained" channel.

@tcroft2165 now put a turbo on it...
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I think he only mentioned increased low load fuel efficiency, cylinder walls have less fiction.
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Peder Hansen that's not true. Good engine performance doesn't necessarily mean bad fuel efficiency. It is an engine of only 2 liter, with low friction cylinders walls, modern exhaust design, direct fuel injection and much more. I think it definitely has great millage.
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that car is a scam
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@NowAndyPlays I meant between VVT (including modern Atkinson cycle) and GM's design, that they would have same effect(?). Also, the intake valve is open during intake and a bit during compression, it's not closing until power/exhaust stroke.
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no but you died
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@Paul-pj5qu Well power itself has nothing to do with efficiency. Depending on what you're comparing the power increase to, it's probably higher than the efficiency gains. On the other hand, just an increase of say, 5 mpg, is a lot.
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@JQB45 Yeah, and that depends entirely on how you drive it, not the fundamental working of the engine itself. If I let my 80 years old grandma drive it, she'll get the same millage as any other small car. But like you said, if I'm buying any car with high horsepower, and I'm of course going to use that performance, then I must be ready to pay for that price of higher overall fuel consumption.
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I hope you don't confuse airplane speed for propeller speed. Do you mean that a cessna prop produces 37 lb at 2hp, at zero airplane speed? And I hope you mean that if prop speed goes up but airplane speed doesn't it will NOT produce 25 times more thrust at 50hp than 2hp? Please clarify.
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I think they took the expression "aim for the stars" a little too literally.
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@Cerberus984 well I guess you could see it that way...
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@sankeelchavan6150 actually, you want as quick flame propagation as possible, as temperature and pressure is higher (the more the better). That is one reason high compression ratio engines are more efficient. This is exactly how Mercedes managed to get about 45% thermal efficiency from their new F1 engine, video on this channel.
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@sankeelchavan6150 your last points are the actual reason for decreased efficiency - knock - which should not happen in a correctly designed engine.
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@sankeelchavan6150 Neither have I stated it :) With your last points I meant that you said the hot air leads to knock, which is completely true. I wanted to clarify that this is the reason why thermal efficiency decreases, and not because of the faster flame propagation. All good man.
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@sankeelchavan6150 No it doesn't work like that. If it results into then knock thermal efficiency will decrease, yes. But you are saying that TE will decrease because there will be a larger temperature difference between gases and coolant which will result in greater heat loss, then that is not the case. According to thermodynamics a larger temperature difference will result in higher TE mainly because the time intervall for burning will significantly decrease and it will actually do the opposite as you stated, much less heat will actually be wasted because there simply isn't enough time = energy must go somewhere = turns into pressure = more work (higher TE). If you want more proof, first of watch that Mercedes F1 video (it's interesting) and do research about energy conversion systems as thermal plants, and you'll see. It's easy to get it the wrong way, I hope this is clarifying :)
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@sankeelchavan6150 First of you need to get one thing straight. A higher pressure, higher compression ratio engine will basically always be more efficient. If you look at the figures, the hybrid system provides an increase from 44% to 50% TE, the engine does the rest (nearly 50% more efficient than most engines). Also, this has has nothing to do with engines lasting longer, the F1 engines last so short because they have extreme power output compared to their size (and therefore all problems that come with that, like knock and tolerance). This is the only reason for short life (yes I'm aware of that increasing pressure so fast might lead to mechanical issues, but not as much if power levels stay the same. The F1 engine use this technology to both get higher efficiency and more power, but it's possible to choose one). Thirdly, TE does not increase on paper while decreasing in practice, absolutely not. Either it increases or decreases, and it has been tested in real life to rise in efficiency. 44% for engine alone is real. Lastly. The better valve airflow, air-fuel mixing and therfore the sudden and huge increase in pressure can and does only one thing when it comes to TE - increasing it! It cannot do both, decrease and increase at the same time.
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Well first their not "slow" and secondly, even if they are slow compared to rotary engiens, piston engines compensate with torque so power is still high.
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exactly the effect would be the same?
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doubt it is lower than 25 mpg, as this is not a heavy car and uses only 5 l modern engine. How much power it can generate is not of that much importance as everything is nearly exactly the same (weight, friction) internally compared tona lower power v8. The turbo is the difference.
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@RS-nq8xk ?
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@RS-nq8xk why that? You know, turbo is spooled up by the exhaust gasses; the energy left in them. Yes, a little back pressure is created but that doesn't affect the engine much as the turbo isn't driven by the engine "forcing" out exhaust.
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Having a top speed of 300 mph means it doesn't have more power for higher speeds, so cruising at that speed would require constant 1600 hp of power. Consumption, based on typical figures, would be 400 l (~100 gallons)/h. This is all I can say.
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@blu3flare25 That's not what I said. Read again. You seem to confuse fuel efficiency with fuel consumption. Fuel consumption is always higher the more power an engine has, absolutely. But the amount of fuel burned compared to the work or power done is thermal efficiency. A large 6.2 v8 that produces 300 hp will consume less than a 400 hp 2.0 i4 at full throttle for both. But not 25% less as it seems like. The i4 will do it at a higher thermal efficiency, consuming less fuel for the specific power level than the v8.
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freezeme360 exactly my point, well said!
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Peder Hansen Didn't you read my comment? Pretty much everything is equal except the higher boost level on the 400 hp one. That does not in any way reduce fuel efficiency. Remember, if you floor it, it wall have higher fuel consumption, but the efficiency stays the same!
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@blu3flare25 Yes. Btw I'm comparing horsepower to fuel consumption.
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Peder Hansen I don't need to know about exactly this engine to understand how they work. I am familiar with the same type pf engines, this isn't something unique. Of course there are many other differences, but I'm talking about the significant ones. Everything else is very equal, if the 400 hp 2.0 uses extra fuel to prevent knocking, them yes, I agree. But this is far from always true. Hardware tuning does not significantly impact fuel efficiency, it's not the main source of power. It's there mainly to maintain optimal AFR and maybe, prevent knocking. Also, your statement about that fuel efficiency is very deep down in priority is completely taken out of your ass, absolutely false. Today's small cylinder high performance cars are all about fuel efficiency while having power, that's the main reason they build small i4s!
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