Max power, at 10500RPM or higher than 10500RPM?

[Tommy Cookers]

compared with 'old' F1
in current F1 the energy converted to work is higher because the heat dumped in cooling and exhaust is far lower .....
because the fuel is given excess air ie the AFR is far higher than 14.7

ie what is being called 'combustion' isn't 'strongest' in these engines at 14.7 AFR
that's how the 'old' rules as per Brian Lovell etc don't apply

the current design approach wouldn't work NA
great downsizing thermal and mechanically is needed, this enabled by the unusually efficient high boost
etc etc etc

[gruntguru]

The present forced induction ICE is fuel restricted to a maximum power speed of somewhere between 10500rpm and 15,000rpm, which is 4500rpm below its permitted maximum RPM of 15000.

Correction in red.

“None of this applies to the current F1 (power unit)”. On the contrary, all of it applies to the current F1 (power unit). We are still talking about an ICE that burns fuel to make power. The differences, while the NA ICE was always air restricted by design/optimised/tuned to achieve maximum power speed at a point 500rpm bellow the maximum RPM it could safely withstand for at least a race distance, and or whatever maximum RPM that was imposed.

The current engines are designed to operate with significant amounts of excess air throughout the normal operating region. This means that small changes (say +or-10%) in airflow at a particular speed (say 11,000 rpm) have very little effect on the power output. On the other hand, a similar change in fuel flow will produce approximately +or- 10% change in power.

Furthermore, if we ignore changes in BTE, the airflow required to produce the same AFR and power all the way from 10,500 to 15,000 is constant. With increasing revs and constant airflow, the air mass inducted per cycle will reduce (as noted by TC on many occasions). As a result, boost pressure needs to reduce to maintain constant airflow as revs increase above 10,500. This is even more true since the introduction of variable intake runners allowing correct wave tuning at all rpm.

The consequence of the above is that breathing ability plays almost no part in the designer's choice of operating rpm. The two main criteria in making this choice are:
1. Widest possible power band to reduce gearshifts. The ideal would be peak power near 12,750 rpm and near-constant power from 10,500 to 15,000.
2. Reducing mechanical (and possibly thermodynamic) efficiency as rpm increase. Because of this the designer will choose a lower peak-power-speed, slightly above 10,500 and an operating range from just below 10,500 to somewhere above the peak-power-speed.

So I agree with TC - none of that airflow-limited power curve stuff applies to current F1.

[saviour stivala]

“None of that ‘airflow-limited power curve stuff applies to current F1’ who said it did?. I said that the NA 2.4l V8 was air limited while the present power unit is fuel limited.

[Tommy Cookers]

..... the present power unit is fuel limited.

not in the sense that afaik you imply

increasing the fuel ratio from lean to stoichiometric (your 14.7) doesn't increase the power - it reduces it
because cooling must be increased (more than fuel increase) and so there is less heat left for conversion to work

100 kg/hr fuel burned at stoichiometric ratio (your 14.7) gives less power than 100 kg/hr fuel burned lean ie 20 or 25 AFR
in these 'heat dilution' F1 engines

hydrogen or methane fuels allow even greater heat dilution ie could be burned much leaner than gasoline
potentially gaining further efficiency/power
this assuming turbocharging efficiency is maintained - the boost being correspondingly even higher than F1's
energy loss to coolant can be entirely eliminated by (sufficient) heat dilution eg in some CI engines

[saviour stivala]

'100kg/h fuel burned at stoichiometric ratio (14.7:1) give/produces the strongest combustion possible on regular pump fuel, and with these present power units that point is reached at 10500rpm.

[hollus]

Tommy’s point was about heat loss to the cylynder walls, if I understand it correctly. Only heat that is produced by combustion and not lost to the walls goes on to propel the car.

[saviour stivala]

Tommy’s point was about heat loss to the cylynder walls, if I understand it correctly. Only heat that is produced by combustion and not lost to the walls goes on to propel the car.

‘100kg/h regular pump fuel burned at 20 or 25:1 air/fuel ratio gives more power than 100kg/h regular pump fuel burned at stoichiometric (14.7:1) air fuel ratio’. OK.I give-up. Over and out.

[Just_a_fan]

If you burn lean, you burn hotter, don't you? I think that's the point.

[Jolle]

We don’t know if the mixture gets leaner above 10.500 rpm. With the turbo and the H motor, they could regulate the amount of air and have a flat mixture curve all trough the powerband. The pressure would drop above 10.500.

[saviour stivala]

The mixture can only get leaner past the 10500rpm mark because the number of combustions per minute increases but the fuel flow does not. That is why 10500rpm is the maximum power speed.

[Zynerji]

The mixture can only get leaner past the 10500rpm mark because the number of combustions per minute increases but the fuel flow does not. That is why 10500rpm is the maximum power speed.

Your just baiting us, right?

On the surface, it's seems like that would be the case, but I would only think so if Mass Air Flow scaled with RPM.

[Jolle]

In the current setup it’s even possible to make the mixture richer past 10.500 rpm or choose how rich when and where you want the bang. The H unit gives almost unlimited control over the amount of air.

[gruntguru]

The mixture can only get leaner past the 10500rpm mark because the number of combustions per minute increases but the fuel flow does not. That is why 10500rpm is the maximum power speed.

Within sensible limits - the mixture can be whatever the engine designer chooses - at any engine speed. All he has to do is increase or reduce the manifold pressure.

[gruntguru]

'100kg/h fuel burned at stoichiometric ratio (14.7:1) give/produces the strongest combustion possible on regular pump fuel, and with these present power units that point is reached at 10500rpm.

This is not correct. If you have a fixed quantity of fuel in the chamber and vary the AFR by varying the amount of air, the "strongest combustion" occurs with excess air. For one thing - at the stoichiometric ratio, a significant percentage of the fuel will remain unburned. This has been known since the days of carburettors - the task of obtaining best economy is the same - how do you extract the most energy from a given quantity of fuel. See image below.

The reverse is the case when you have a fixed quantity of air and you vary the fuel. The "strongest combustion" occurs with excess fuel. For one thing - at the stoichiometric ratio, a significant percentage of the air will remain unburned. This has been known since the days of carburettors - the task of obtaining best power is the same - how do you extract the most energy from a given quantity of air. See image below.



Note also that the above image represents "old" technology. Lean-burn was limited by poor ignition and slow flame speed. With modern lean-burn techniques like TJI, the best efficiency point has moved way beyond the 15.4:1 (Lambda = 1.07) shown. See image below.

[saviour stivala]

In the current setup it’s even possible to make the mixture richer past 10.500 rpm or choose how rich when and where you want the bang. The H unit gives almost unlimited control over the amount of air.

Extremely interesting that the mixture can be made even richer past 10500rpm with the increase in number of combustions having to share the same amount of fuel flow in accordance with the increase in RPM. Hoping that some serious technical enlightenment will be shared on here on this suggestion.