Mercedes F1

[naukkis79]

What do you mean by "100KG/s gas"?

F1 are fuel flow limited to 100KG/s gas. That amount of gas has thermal energy about 1240kW. F1-egines ICE outputs are somewhere about 750Hp, that's 550KW. So internal combustion engine efficiency is 550kw/1250kW=~44% at WOT. Turbine need to extract some 65kW on top of that to achieve 50% thermal efficiency.

[naukkis79]

On the other hand, if the engine and all systems can actually reach 50% fuel efficiency under a full power operating condition, what can it do under a maximum economy operating condition, 80%??? You are saying that the parameters for max power and max efficiency are the SAME!

F1 engine is fuel flow limited, only way to increase it's power output is with increased efficiency. And combustion engine is most efficient at WOT, if not it's due excessive richness of fuel mixture to calm engine down or to prevent pre-ignition. You can and should build engine to get work without that cheap shortcut to make it survive at WOT.

[140Air]

What do you mean by "100KG/s gas"?

F1 are fuel flow limited to 100KG/s gas. That amount of gas has thermal energy about 1240kW. F1-egines ICE outputs are somewhere about 750Hp, that's 550KW. So internal combustion engine efficiency is 550kw/1250kW=~44% at WOT. Turbine need to extract some 65kW on top of that to achieve 50% thermal efficiency.

So, you mean 100kg/s of fuel! That's what I thought you meant. But that is 3,600 times too high. But, that is a small detail.
Where did you get your 44% figure? That requires way higher peak temperatures in an Otto cycle engine than can be sustained by steel chambers. Granted they could be using ceramic or other liners. But then they have to have greatly increased the effective octane of ordinary (within the FIA formulary ingredients) gasoline.

Also, WOT does NOT, NOT mean maximum power! The article was reporting results on a test bench. It doesn't even have to be an engine in race trim.

[GARY C]

When did 50% become "more than half"?

I think the 50% thermal efficiency vs 35.5% is a little misleading, the Cup engines or in the 35.5 range but they are NA engines and therefore cannot recuperate the exhaust heat back into power through a turbo and then as F1 does add an electric motor to boot. I would be curios what the F1 engine would show if it was NA?

[naukkis79]

So, you mean 100kg/s of fuel! That's what I thought you meant. But that is 3,600 times too high. But, that is a small detail.

Only a little brainfart....

Where did you get your 44% figure? That requires way higher peak temperatures in an Otto cycle engine than can be sustained by steel chambers. Granted they could be using ceramic or other liners. But then they have to have greatly increased the effective octane of ordinary (within the FIA formulary ingredients) gasoline.

That's what engine manufacturers report. Peak temperatures are in control with leaner-than stoich afr rates with something different than normal ignition - they either use turbulent jet ignition to fastburn lean mixture or pure detonation ignition. Compression ratios are also in region of 15:1.

Also, WOT does NOT, NOT mean maximum power! The article was reporting results on a test bench. It doesn't even have to be an engine in race trim.

Point is that internal combustion engine achieves it's best thermal efficiency at full power. It's way harder to achieve part-power efficiency.

[140Air]

Point is that internal combustion engine achieves it's best thermal efficiency at full power. It's way harder to achieve part-power efficiency.

This is absolutely wrong. Normally, the highest thermal efficiency occurs at the torque peak. For F1 where the max power is limited by the fuel flow limit it would make no sense to make the torque peak occur at the power peak (which can be done). It would only unnecessarily diminish the max torque and the acceleration.

[naukkis79]

This is absolutely wrong. Normally, the highest thermal efficiency occurs at the torque peak. For F1 where the max power is limited by the fuel flow limit it would make no sense to make the torque peak occur at the power peak (which can be done). It would only unnecessarily diminish the max torque and the acceleration.

As they are fuel flow limited both max torque and max power are happening at 10500rpm.

Think it, as they are fuel flow limited and nothing else is limited max power will be at highest thermal efficiency point.

And why 10500rpm? At lower revs they are limited to less fuel flow, and at higher revs limited to same fuel flow with more mechanical losses.

[140Air]

This is absolutely wrong. Normally, the highest thermal efficiency occurs at the torque peak. For F1 where the max power is limited by the fuel flow limit it would make no sense to make the torque peak occur at the power peak (which can be done). It would only unnecessarily diminish the max torque and the acceleration.

As they are fuel flow limited both max torque and max power are happening at 10500rpm.

Think it, as they are fuel flow limited and nothing else is limited max power will be at highest thermal efficiency point.

And why 10500rpm? At lower revs they are limited to less fuel flow, and at higher revs limited to same fuel flow with more mechanical losses.

What you are saying is that by limiting rpm to where the max torque is, you automatically get max power at that rpm. This is trivial! But, the same fuel flow limit will allow much more torque at a lower rpm where the engine will be more tractable and provide much better acceleration. Why tune the engine to be weak below the power peak? Thermal efficiency is normally highest when friction losses are lowest. RPM produces friction losses with an exponent greater than one.

[naukkis79]

What you are saying is that by limiting rpm to where the max torque is, you automatically get max power at that rpm. This is trivial! But, the same fuel flow limit will allow much more torque at a lower rpm where the engine will be more tractable and provide much better acceleration. Why tune the engine to be weak below the power peak? Thermal efficiency is normally highest when friction losses are lowest. RPM produces friction losses with an exponent greater than one.

That's not what I'm saying. Max torque happens at 10500rpm because that is lowest rpm which allow full fuel flow. Fuel flow is limited to lower level at less than 10500 rpm. And max power happens at that same rpm not because rpm is limited but because same fuel flow at higher rpm with increased mechanical loss and probably lower thermal efficiency due lower MBT.

F1-engines gearing is so that upper gear drops rpm to exactly 10500 rpm to allow full fuel flow and max rpm is what is gear steps, usually about 12000rpm, with higher gears bit lower to allow being closer to max power at 10500rpm.

As you say efficiency is easier to get at lower rpm range, and because they didn't want to have truck-like engine revs they created fuel flow limits to force engines to over 10500rpm.

[ptuomov]

What you are saying is that by limiting rpm to where the max torque is, you automatically get max power at that rpm. This is trivial! But, the same fuel flow limit will allow much more torque at a lower rpm where the engine will be more tractable and provide much better acceleration. Why tune the engine to be weak below the power peak? Thermal efficiency is normally highest when friction losses are lowest. RPM produces friction losses with an exponent greater than one.

That's not what I'm saying. Max torque happens at 10500rpm because that is lowest rpm which allow full fuel flow. Fuel flow is limited to lower level at less than 10500 rpm. And max power happens at that same rpm not because rpm is limited but because same fuel flow at higher rpm with increased mechanical loss and probably lower thermal efficiency due lower MBT.

F1-engines gearing is so that upper gear drops rpm to exactly 10500 rpm to allow full fuel flow and max rpm is what is gear steps, usually about 12000rpm, with higher gears bit lower to allow being closer to max power at 10500rpm.

They should drop the rpm to slightly below 10500 rpm if that’s peak power and efficiency point because that would increase both average power and average efficiency.

[peejay]

What you are saying is that by limiting rpm to where the max torque is, you automatically get max power at that rpm. This is trivial! But, the same fuel flow limit will allow much more torque at a lower rpm where the engine will be more tractable and provide much better acceleration. Why tune the engine to be weak below the power peak? Thermal efficiency is normally highest when friction losses are lowest. RPM produces friction losses with an exponent greater than one.

That's not what I'm saying. Max torque happens at 10500rpm because that is lowest rpm which allow full fuel flow. Fuel flow is limited to lower level at less than 10500 rpm.

Just to clarify: Fuel flow limits are RPM dependent?

[140Air]

That's not what I'm saying. Max torque happens at 10500rpm because that is lowest rpm which allow full fuel flow. Fuel flow is limited to lower level at less than 10500 rpm. And max power happens at that same rpm not because rpm is limited but because same fuel flow at higher rpm with increased mechanical loss and probably lower thermal efficiency due lower MBT.

F1-engines gearing is so that upper gear drops rpm to exactly 10500 rpm to allow full fuel flow and max rpm is what is gear steps, usually about 12000rpm, with higher gears bit lower to allow being closer to max power at 10500rpm.

As you say efficiency is easier to get at lower rpm range, and because they didn't want to have truck-like engine revs they created fuel flow limits to force engines to over 10500rpm.

That would explain the illogical power and torque curves. It is not just the fuel flow limit, but also the low rpm fuel flow limit. Now it makes sense.
However, this makes the test bench engine all the more interesting since it is free of rules and can pursue best efficiency. It also means the test engine should not resemble the race engine at all with respect to maximum efficiency and where in the rpm range it occurs.

[MadBill]

This "oil as fuel" article touches on several points in preceding posts: http://www.motorsportmagazine.com/opini ... RenaultOil

Myself, I liked the Pro Stock ploy of some years back of running used Top Fuel oil to allow its significant nitromethane contamination to vent into the cylinders...

[Ron E]

This "oil as fuel" article touches on several points in preceding posts: http://www.motorsportmagazine.com/opini ... RenaultOil

Myself, I liked the Pro Stock ploy of some years back of running used Top Fuel oil to allow its significant nitromethane contamination to vent into the cylinders...

I remember that. It seems the tech guys had no appreciation for recycling.

[naukkis79]

Just to clarify: Fuel flow limits are RPM dependent?

Yes

https://abulafiaf1.wordpress.com/2012/0 ... derations/