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

[saviour stivala]

<Mod intro: This topic is the discussion on the location (in RPM) of max power in the current (2014-2019) breed of F1 power units. Split form the thread about the use of pneumatic valves.>

10500 rpm is the maximum power speed of the present power unit, above 10500 rpm it is not possible to produce any more power. If it wasn't for the maximum fuel flow rate rule set at maximum of 10500 rpm these power units would have been designed to run and produce their maximum power output at a lower maximum rpm. and they would have achieved a much better efficiency percentage number.

[hollus]

10500 is max fuel. Max power is probably a bit over 10500 as they want to hit 10500 after the upshift, so they mostly live above 10500rpm, but let’s not derail too much for a few hundred rpm.

[saviour stivala]

10500 is max fuel. Max power is probably a bit over 10500 as they want to hit 10500 after the upshift, so they mostly live above 10500rpm, but let’s not derail too much for a few hundred rpm.

A maximum fuel flow rate of 100kg/h @ 10500 rpm sets the maximum power speed at that maximum rpm. Above that maximum rpm they cannot produce any additional power. it is normal practice to upshift at above maximum power speed. With an NA engine upshifts are normally made at 500 rpm above max power speed.

[Tommy Cookers]

10500 rpm is the maximum power speed of the present power unit, above 10500 rpm it is not possible to produce any more power. If it wasn't for the maximum fuel flow rate rule set at maximum of 10500 rpm these power units would have been designed to run and produce their maximum power output at a lower maximum rpm. and they would have achieved a much better efficiency percentage number.

where would this 'much better efficiency percentage number' come from ?
imagine we redesign to halve the rpm .....

this would need double the induction pressure ('boost') to double the mep
doubling the mep would double the frictional loads on the power stroke - so frictional power there wouldn't fall
piston compression work (already very high) would be more than doubled - so frictional power there would rise
doubled mep would also need bigger bearings and crankshaft - so more frictional load there (ok not more power)
compressor power would more than double - and compressor efficiency would plummet (unless it became 2 stage)
ie there is no increase in recovery from raising boost - and recovery will fall where compressor efficiency falls
and this all assumes that detonation can be managed without efficiency loss - despite the doubled mep

the engine rules weren't written by fools

[gruntguru]

10500 is max fuel. Max power is probably a bit over 10500 as they want to hit 10500 after the upshift, so they mostly live above 10500rpm, but let’s not derail too much for a few hundred rpm.

A maximum fuel flow rate of 100kg/h @ 10500 rpm sets the maximum power speed at that maximum rpm. Above that maximum rpm they cannot produce any additional power. it is normal practice to upshift at above maximum power speed. With an NA engine upshifts are normally made at 500 rpm above max power speed.

The fuel (energy) flow rate is constant from 10,500 to 15,000 rpm. 10,500 is the optimum speed to make maximum power since friction increases with speed. However it is probable that the engine is optimised for a slightly higher speed - say 11,000 to maintain the highest possible "average power" during acceleration through the gears - say 10,500 to 11,500. This "optimisation" would include selection of camshaft profiles, valve and port sizes etc. This would cost a small amount of "peak power" compared to optimising for 10,500, but would result in higher "average power" across the band from 10,500 to 11,500.

[henry]

10500 is max fuel. Max power is probably a bit over 10500 as they want to hit 10500 after the upshift, so they mostly live above 10500rpm, but let’s not derail too much for a few hundred rpm.

A maximum fuel flow rate of 100kg/h @ 10500 rpm sets the maximum power speed at that maximum rpm. Above that maximum rpm they cannot produce any additional power. it is normal practice to upshift at above maximum power speed. With an NA engine upshifts are normally made at 500 rpm above max power speed.

The fuel (energy) flow rate is constant from 10,500 to 15,000 rpm. 10,500 is the optimum speed to make maximum power since friction increases with speed. However it is probable that the engine is optimised for a slightly higher speed - say 11,000 to maintain the highest possible "average power" during acceleration through the gears - say 10,500 to 11,500. This "optimisation" would include selection of camshaft profiles, valve and port sizes etc. This would cost a small amount of "peak power" compared to optimising for 10,500, but would result in higher "average power" across the band from 10,500 to 11,500.

And, as we’ve discussed elsewhere, it’s useful for power to be the same before and after upshifts to help maintain constant tractive effort through the shift. This helps drivers to upshift any time they like, even on the entry to turn 9 at Barcelona.

[gruntguru]

Good info on PVRS - thanks SS.

Regarding power peak. "Fuel flow" and "power potential" have a proportional relationship which is independent of rpm. Under constant fuel flow conditions (eg between 10,500 and 15,000) "actual power" falls with increasing rpm but only because of increasing friction and other factors associated with airflow and combustion.

Because the slope of this section of the power curve falls more gently than the curve below 10,500 (which is governed by fuel flow regulations), the engines (at max demand) must be operated above 10,500 (say 10,500 to 11,500). Given this requirement it is clear that optimising for peak power at somewhat higher than 10,500 would be advantageous.



<Response on peak power from stivala, has to go here because of the thread split>

And finally, re ‘max power speed’, at its max power speed of 10500rpm the V6 will produce 30500 combustions/min. at 12000rpm it will produce 36000 combustions/min. 4500combustions/min more. Higher rpm equates to more fuel burn in the same amount of time. That fuel flow rate as per regulations is just not there so it is not possible for any additional power to be produced above its max power speed.

[Tommy Cookers]

..... optimising for peak power at somewhat higher than 10,500 would be advantageous.

this (as I say on these occasions) imo implies with rpm exceeding 10500 and peaking typically c. 12200 .....

reducing air charge per cycle (by reducing boost) or ...
maintaining charge by leaning or maybe ...
increasing exhaust pressure relative to boost (for managed underscavenge) or ...
increasing fuel rate (having used less than 100 kg/hr at 10500)
or some combination of the above

optimising for peak power above 10500 (eg by exhaust tuned length effect) increases the charge/fuel rate mismatch as above
ok having eg inlet tract only at tuned length above 10500 would reduce this mismatch (but at some 10500 PU efficiency cost)

the mismatch is somewhat relieved as ...
the ICE is not in thermal equilibrium at 10500 rpm/100 kg/hr - (this charge/fuel rate combination is useable only briefly)

[saviour stivala]

When formulating the new engine specification rules the rule makers amended the “maximum100kg/h fuel flow” rule by adding the maximum RPM (10500) at which the maximum fuel flow could be reached, when doing this they also upped (amended) the maximum limit of 12000rpm up to 15000rpm. The rule makers had back than realized, through their fear of the engines going to have too much a drastic reduction of exhaust scream, that the engine designers were going to be pushed into designing for the least possible maximum power speed because of the new fuel restriction rules (100kg maximum fuel load and 100kg/h maximum fuel flow rate). To achieve the best power outputs with the best possible efficiency. It would have been logical for the engine designers to opt for the least possible maximum power speed, because the maximum 100kg/h mandated fuel flow rate would have given them a bigger volume of fuel flow rate requirement at lower RPM and unlimited boost.
Higher RPM equates to more fuel burn in the same amount of time.

[gruntguru]

Higher RPM equates to more fuel burn in the same amount of time.

I don't understand this statement. Did you mean to say something else?

If fuel flow rate is constant across a range of RPM, the fuel burn per unit time is also constant regardless of RPM.

[saviour stivala]

“Higher RPM equates to more fuel burn in the same amount of time” Goes to show that if the engine is running at higher RPM to produce any additional power at the higher RPM it needs more fuel to burn. If the additional fuel flow needed at the higher RPM is not there the engine will simply lean-out at the higher RPM.
And yes, if fuel flow rate is constant across a range of RPM (gapped above/past the maximum power speed-10500rpm) the fuel burn per unit time is also constant (as gapped) regardless of RPM. And that is precisely why these power units run at a 10500rpm maximum power speed and above which they cannot add/produce any additional power output.

[henry]

“Higher RPM equates to more fuel burn in the same amount of time” Goes to show that if the engine is running at higher RPM to produce any additional power at the higher RPM it needs more fuel to burn. If the additional fuel flow needed at the higher RPM is not there the engine will simply lean-out at the higher RPM.
And yes, if fuel flow rate is constant across a range of RPM (gapped above/past the maximum power speed-10500rpm) the fuel burn per unit time is also constant (as gapped) regardless of RPM. And that is precisely why these power units run at a 10500rpm maximum power speed and above which they cannot add/produce any additional power output.

Last year @mudflap produced a useful resource by analysing the video telemetry of Vettel’s pole lap at Singapore. Here’s a link viewtopic.php?p=748135#p748135

I analysed that data to look at the power curve. Here’s my most recent post on that. viewtopic.php?p=748502#p748502

I found the power peak above 11,000 rpm. This finding is consistent with the reasoning put forward above by @tommy cookers and @gruntguru.

The figures I got for absolute power level are subject to many errors based on assumptions on mass, CdA etc but the shape of the curve is much less sensitive.

These are not normally aspirated power units running around stoichimetric. They run very lean with the air supply under constant management by variable boost pressure and blow off recirculating. They can choose where to put maximum power and I’m convinced from my analysis that they put it midway between 10500 and their upshift rpm, probably 11800 nowadays. Peak power is less important than the average power, both from the ICE and the MGU-H, and this is what they optimise for.

[saviour stivala]

Suggesting that a particular formula car/one engine peak power was being produced at 11500 rpm means that car/engine maximum fuel flow has been shifted from the mandatory 10500 rpm to 11500 rpm.

[henry]

Suggesting that a particular formula car/one engine peak power was being produced at 11500 rpm means that car/engine maximum fuel flow has been shifted from the mandatory 10500 rpm to 11500 rpm.

Maybe so. I can’t tell from my calculations how the power was achieved only that it peaks at around 11200 rpm.

We have a difference between theories and an experimental result. The result supports several of the theories and is at odds with just one, that peak power occurs at 10500 rpm because of the mandated fuel rate prescription. The usual course of action in this circumstance is to explore the experimental method to see whether it is flawed. I’m happy to do that.

[Jolle]

maybe very off topic from the original question, but I think this fuel flow limit is one of the key things mercedes got right compared to Renault and Ferrari in 2014. It is very counter intuitive that with every extra rpm above 10.500 the fuel per cycle is less. To keep the golden 1/14 fuel/air ratio, they have to limit the air above that rpm (lower boost) or run less then a 1/14 ratio. This combined that no fuel must go to waste. Compared to more rpm = more power and unburned fuel is no problem (even good for cooling) in the old N/A era

this is one of the reasons I do like the latest formula, a whole new way of thinking.