3 cylinder engine.

[Tommy Cookers]

well the piston CR is limited by the rules
and by the engineering practicalities eg the volume required for valve motion

[Jolle]

well the piston CR is limited by the rules
and by the engineering practicalities eg the volume required for valve motion

limited with a max CR, not a minimal. It's set on 1:18, to rule out diesel I guess.... I assume that F1 PU's don't run higher then 1:10 or something.

[wuzak]

First of all, you won't get higher revs in a turbo charged engine if you make it smaller. Power is a result of the amount of air/fuel you can get trough the engine. Boost pressure does this. In theory a 7l V8 will have the same power as a 1l 3L with the same boost.

This is not correct.

a turbo 7l V8 will have, roughly speaking, the same power as a turbo 1l 3L if they have the same boost and mass air flow.

To have the same mass air flow as the 7l V8 the 1l 3L will have to rev higher.

[wuzak]

You are forgetting that an I3 would be too small to become a stressed member.

I remember Adrian Newey saying that the small V6 was right on the limit.

The V6 should be better as a stressed member than the longer V8s and V10s.

The bank angle chosen was specifically for this reason.

Newey was opposed to the in-line 4 originally proposed, as it lacked strength in some directions.

The other side of the coin is the extended wheelbases the current cars have. This leads to a longer gearbox connection to the engine, which means that it is heavier to get the strength required.

[Jolle]

First of all, you won't get higher revs in a turbo charged engine if you make it smaller. Power is a result of the amount of air/fuel you can get trough the engine. Boost pressure does this. In theory a 7l V8 will have the same power as a 1l 3L with the same boost.

This is not correct.

a turbo 7l V8 will have, roughly speaking, the same power as a turbo 1l 3L if they have the same boost and mass air flow.

To have the same mass air flow as the 7l V8 the 1l 3L will have to rev higher.

No it won't, the pressure in the cylinders is just higher. Same air/fuel but in a smaller cylinder... same energy. If lower cylinder pressure would give more power with the same fuel flow, the current F1 PU's would rev to 15.000 rpm. Somehow low revs and high pressure is good for power and efficiency

[wuzak]

First of all, you won't get higher revs in a turbo charged engine if you make it smaller. Power is a result of the amount of air/fuel you can get trough the engine. Boost pressure does this. In theory a 7l V8 will have the same power as a 1l 3L with the same boost.

This is not correct.

a turbo 7l V8 will have, roughly speaking, the same power as a turbo 1l 3L if they have the same boost and mass air flow.

To have the same mass air flow as the 7l V8 the 1l 3L will have to rev higher.

No it won't, the pressure in the cylinders is just higher. Same air/fuel but in a smaller cylinder... same energy. If lower cylinder pressure would give more power with the same fuel flow, the current F1 PU's would rev to 15.000 rpm. Somehow low revs and high pressure is good for power and efficiency

Same boost = same pressure.

If they have the same air/fuel [mass flow rate] and boost, the 1L engine will need to have 7 times the rpm to take the volumetric flow rate.

[Jolle]

This is not correct.

a turbo 7l V8 will have, roughly speaking, the same power as a turbo 1l 3L if they have the same boost and mass air flow.

To have the same mass air flow as the 7l V8 the 1l 3L will have to rev higher.

No it won't, the pressure in the cylinders is just higher. Same air/fuel but in a smaller cylinder... same energy. If lower cylinder pressure would give more power with the same fuel flow, the current F1 PU's would rev to 15.000 rpm. Somehow low revs and high pressure is good for power and efficiency

Same boost = same pressure.

If they have the same air/fuel [mass flow rate] and boost, the 1L engine will need to have 7 times the rpm to take the volumetric flow rate.

I'm sorry, but that is not how a turbo engine works, that is how a NA works.

A turbo enige forces the air into the cylinder. For instance, if you have a NA 1L engine, at 10.000 revs, you have 0.5L of air (1 bar) per cycle, 10.000 cycles per minute is 5000 liters of air at 1 bar which will give for instance 150bhp.

If you turbocharge that with 2 bar at 10.000rpm you will have 1L of air per cycle at pushed into the engine (compressed into 0,5L) which gives 10.000 liters of air per minute which will double the power and gives you a theoretical 300 bhp.

To keep the combustion pressure the same, the compression ratio has to come down the same amount. lets say the NA engine has a ratio of 1:14, the turbo with 2 bar of pressure has a ratio of 1:7. This way the air/fuel mixture will be compressed the same, just with twice the amount of air/fuel in the cylinder, so twice the amount of energy.

So as you see, revs at a turbo engine is unimportant (in theory), it's all about boost. If you want more power, you turn op the boost and lower the compression ratio.

[Tommy Cookers]

high boost/low CR is a recipe for power at the expense of engine efficiency
(often useful in aircraft - and some relieved inefficiency by exhaust recovery turbine or (at high speed) exhaust 'jet' effect)

the cylinder doesn't know whether it's in a turbo engine or an NA engine - only the designer does
many centrifugal induction-impeller engines and turbo engines gave/give only NA-level induction pressures even at sea level

F1 could have existing engines designed around lower boost and a 13000 - 15000 rpm operating range
or even to run NA at eg 22000 rpm (with NA V8 bore:stroke ratio etc to allow this)
but the rules fixing fuel rate at 10500 prevent these design routes
because eg at 15000 rpm the boost would need to be c. half the 10500 boost (to maintain the AFR)

the high boost high pressure engine has higher piston friction forces, so friction power loss is not low

the best defence for the high pressure advocate is that with enough pre-cylinder charge cooling the CR may be kept high
and of course charge heating on in-cylinder compression is (relatively) independent of increased boost
ie high boost/ultra lean mixture scores very well here
(it also gains thermodynamically from the better in-cycle gas composition)

the benefits of ultra lean mixture are greater at present boosts than at lower boosts or NA
but they rely on the very efficient recovery turbine enabled by MU-H action and a very efficient compressor
higher boosts than current would be subject to reduced efficiencies or require multiple stages

[Jolle]

high boost/low CR is a recipe for power at the expense of engine efficiency
(often useful in aircraft - and some relieved inefficiency by exhaust recovery turbine or (at high speed) exhaust 'jet' effect)

the cylinder doesn't know whether it's in a turbo engine or an NA engine - only the designer does
many centrifugal induction-impeller engines and turbo engines gave/give only NA-level induction pressures

why, if a low CR is not efficient, do the current F1 teams all go for lowest revs they can be which means the highest cylinder pressure and therefor the lowest CR?

my theory is that you must have as much of a burn inside the cylinder before it hits the bottom, whether it's at 1:7 at 2 bar inlet or 1:8 at 1.9 bar. The lower the revs the more time you have to have a 100% burn. The energy stays the same.

[Tommy Cookers]

I wrote engine efficiency - meaning ICE efficiency not PU efficiency
CR (or really expansion ratio) is fundamental to conversion of heat to work (in any stage of a simple or compound engine)

if the rules dictated a smaller MGU-K then we might see higher rpm/lower boost
though I'm not suggesting that 15000 rpm allows much higher CR than does 10500

remember higher boosts do not give higher recovery (because compressor work rises strongly with boost)

the rules in effect demand a weakly-compounded engine
other levels of compounding are possible, but heavy compounding is/was restricted to CI (eg 15 bar boost Hyperbar CI 2 T ?)
500 bar DI as now allowed might with multiple injections allow an SI engine to have CI type CRs ?

[Jolle]

I wrote engine efficiency - meaning ICE efficiency not PU efficiency
CR (or really expansion ratio) is fundamental to conversion of heat to work (in any stage of a simple or compound engine)

if the rules dictated a smaller MGU-K then we might see higher rpm/lower boost
though I'm not suggesting that 15000 rpm allows much higher CR than does 10500

remember higher boosts do not give higher recovery (because compressor work rises strongly with boost)

the rules in effect demand a weakly-compounded engine
other levels of compounding are possible, but heavy compounding is/was restricted to CI (eg 15 bar boost Hyperbar CI 2 T ?)
500 bar DI as now allowed might with multiple injections allow an SI engine to have CI type CRs ?

I fail to see what the size of the K unit has to do with the rpm or boost of the ICE.

And yes, a lower CR results in a less efficient engine if you don’t change the boost to match it, which is the whole point of a lower CR of a turbo engine.

[Tommy Cookers]

lower boost requires far less compressor power (as repeatedly comes from M-H action)
and much of the time M-K action is powered directly or otherwise from G-H action
so the MGU-H side and the ES side are rather matched in power to the power of the MGU-K side

if the MGU-K was eg limited to 60 kW you wouldn't keep the rest as present
running faster will disproportionately reduce boost needed (work to raise above natural 1.2 bar) and compressor power
running faster and less boost would be expected to allow higher CR/ER as the charge is less heated by the compressor

your last point is at best unrelated to the subject of this thread (how to use current air and fuel flow rates)
indicated efficiency of the ICE is always related to the CR/ER
there's only friction power to be varied by cylinder pressure and rpm
the recovery turbine can recover only a fraction of the excess exhaust energy left by a less-than-maximal ER
said recovery turbine having an CR/ER of 3 or 4 not the cylinder's 13 or 14
remember there's blowdown recovery ie the 'free' recovery that exists without any back pressure

[wuzak]

why, if a low CR is not efficient, do the current F1 teams all go for lowest revs they can be which means the highest cylinder pressure and therefor the lowest CR?

Because the fuel flow rate is on a ramp, and lower rpm means less fuel, which means less power.

They are hardly running at low CRs. The rues had a maximum CR of 18:1 inserted into the rules last year. Which suggests that the manufacturers were working towards that sort of number.

[wuzak]

No it won't, the pressure in the cylinders is just higher. Same air/fuel but in a smaller cylinder... same energy. If lower cylinder pressure would give more power with the same fuel flow, the current F1 PU's would rev to 15.000 rpm. Somehow low revs and high pressure is good for power and efficiency

Same boost = same pressure.

If they have the same air/fuel [mass flow rate] and boost, the 1L engine will need to have 7 times the rpm to take the volumetric flow rate.

I'm sorry, but that is not how a turbo engine works, that is how a NA works.

A turbo enige forces the air into the cylinder. For instance, if you have a NA 1L engine, at 10.000 revs, you have 0.5L of air (1 bar) per cycle, 10.000 cycles per minute is 5000 liters of air at 1 bar which will give for instance 150bhp.

If you turbocharge that with 2 bar at 10.000rpm you will have 1L of air per cycle at pushed into the engine (compressed into 0,5L) which gives 10.000 liters of air per minute which will double the power and gives you a theoretical 300 bhp.

To keep the combustion pressure the same, the compression ratio has to come down the same amount. lets say the NA engine has a ratio of 1:14, the turbo with 2 bar of pressure has a ratio of 1:7. This way the air/fuel mixture will be compressed the same, just with twice the amount of air/fuel in the cylinder, so twice the amount of energy.

So as you see, revs at a turbo engine is unimportant (in theory), it's all about boost. If you want more power, you turn op the boost and lower the compression ratio.

At the same RPM, a 1L turbo engine will require a pressure ratio of 7:1 to the the same mass of air into the cylinder as a 7L non-turbo engine. Assuming the same volumetric efficiency, which probably wouldn't be the case (and would bring down the PR required).

But you specified a 7L turbo and a 1L turbo engine, running the same boost. Same boost = same pressure ratio.

First of all, you won't get higher revs in a turbo charged engine if you make it smaller. Power is a result of the amount of air/fuel you can get trough the engine. Boost pressure does this. In theory a 7l V8 will have the same power as a 1l 3L with the same boost.

[Jolle]

why, if a low CR is not efficient, do the current F1 teams all go for lowest revs they can be which means the highest cylinder pressure and therefor the lowest CR?

Because the fuel flow rate is on a ramp, and lower rpm means less fuel, which means less power.

They are hardly running at low CRs. The rues had a maximum CR of 18:1 inserted into the rules last year. Which suggests that the manufacturers were working towards that sort of number.

Could be, could also be to rule out the use of diesel. Which has more energy per kg but isn’t very F1