## Why do we have a fuel allowance and a max fuel flow rate?

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dave kumar
3
Joined: Tue Feb 26, 2008 1:16 pm
Location: UK

### Why do we have a fuel allowance and a max fuel flow rate?

As far as I understand, the max fuel flow rate of 100kg/hr was put in place to limit the engine power. For a given fuel flow, you can only extract so much energy, so by imposing a max fuel flow rate you impose a limit on the amount of power that can be generated by the power unit.

I think the intention here was to stop teams spending money on developing power units with crazy qualifying modes - I'm thinking of the rumoured 1500+hp qualifying engines of the 80s.

For PU manufacturers, the fuel flow limit rewards those that have the most efficient PUs, which aligns with their commercial aims. Also by having a fuel flow limit, different engines will converge over time in their maximum power output as they approach the theoretical efficiency limits of hybrid power units (somewhere around 50%).

What I don't understand is why we have the fuel allowance for a race (currently 110kg, up from 105kg last year). Every kg of fuel that a car starts with in the race is a weight penalty. A team will calculate the amount of fuel they will need to give the fastest time to the flag. This may include some lift-and-coast fuel saving on some tracks, depending on the fuel consumption - and we know many teams short-fill their cars based on this calculation.

But my point is that the amount of fuel is self limiting. No team is going to carry more fuel than they calculate is the optimal amount so why mandate a maximum?
Formerly known as senna-toleman

Maritimer
Maritimer
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Joined: Wed Sep 06, 2017 8:45 pm

### Re: Why do we have a fuel allowance and a max fuel flow rate?

Had a bigger influence in 14 did it not? Pretty sure when they first came up with a max mass the cars were much more marginal than they are now.

Jolle
Jolle
185
Joined: Wed Jan 29, 2014 9:58 pm
Location: Dordrecht

### Re: Why do we have a fuel allowance and a max fuel flow rate?

think about not knowing what constructors come up with. Without the 100kg limit you could run the ICE constantly and use the H unit to power the K or charge the ES. With the fuel limit that is not efficient.

I also think that the advances they made in tech were greater then expected. There are other now obsolete rules. For instance the max rev. Nobody even comes close to it because of efficiency.

dave kumar
3
Joined: Tue Feb 26, 2008 1:16 pm
Location: UK

### Re: Why do we have a fuel allowance and a max fuel flow rate?

Yes I see your point. In theory, without a race fuel allowance you could turn the ICE in to a generator and run it at max fuel flow (100kg/hour) for the whole race and use the energy storage to mediate the power to the wheels by charging or discharging according to the power requested by the driver.

But this doesn't happen during qualifying, presumably because there is a limit to how much energy can be deployed over a lap. Even without a limitation on how much energy you can deploy from the ES during a lap, in the race you have a weight penalty for extra fuel you burn to charge the ES - so we can get rid of the race fuel allowance right?
Formerly known as senna-toleman

SF Engineer
SF Engineer
14
Joined: Tue Apr 09, 2019 2:10 pm

### Re: Why do we have a fuel allowance and a max fuel flow rate?

dave kumar wrote:
Fri May 17, 2019 9:11 am
As far as I understand, the max fuel flow rate of 100kg/hr was put in place to limit the engine power. For a given fuel flow, you can only extract so much energy, so by imposing a max fuel flow rate you impose a limit on the amount of power that can be generated by the power unit.

I think the intention here was to stop teams spending money on developing power units with crazy qualifying modes - I'm thinking of the rumoured 1500+hp qualifying engines of the 80s.

For PU manufacturers, the fuel flow limit rewards those that have the most efficient PUs, which aligns with their commercial aims. Also by having a fuel flow limit, different engines will converge over time in their maximum power output as they approach the theoretical efficiency limits of hybrid power units (somewhere around 50%).

What I don't understand is why we have the fuel allowance for a race (currently 110kg, up from 105kg last year). Every kg of fuel that a car starts with in the race is a weight penalty. A team will calculate the amount of fuel they will need to give the fastest time to the flag. This may include some lift-and-coast fuel saving on some tracks, depending on the fuel consumption - and we know many teams short-fill their cars based on this calculation.

But my point is that the amount of fuel is self limiting. No team is going to carry more fuel than they calculate is the optimal amount so why mandate a maximum?
The fuel flow limit is 100kg/hr. For simplicity lets take an F1 race to be 2 hours in length.
That means that the engine must average 50kg/hr under the old regulations, and 52.5kg/hr now.

You have a certain percentage of the lap where you are using 100kg/hr, say 60%. Over 2 hours this would mean that you'd need 120kg + the amount you used at partial throttle (let's say 35% for the average). That's 35kg/hr for 40% for the race, so 28kg. So, in total you'd need 148kg of fuel to do the race this way (obviously I am taking lots of assumptions, but the point remains the same: it's probably not possible to do some of the races on the calendar using the full fuel flow limit (even only at full throttle) for the whole race.

This would not be the case if the maximum fuel you could carry was in excess of the result of a calculation like the one shown above. Subsequently, this is also one of the reasons why you see increased race pace under the new regulations.

For qualifying this is not a concern, as the fuel tank can easily carry more fuel than can be used, even if 100kg/hr could be used at all times.

The relationship between fuel effect and the amount of extra power you can get by carrying more fuel is also relatively simple and will result in a theoretical cross-point for each circuit. Should the permitted fuel limit be increased this would be up to the team and its engine manufacturer to decide how much fuel would give the best result. I have no idea what the limit would be, and at that point you would possibly end up with opinions of the engine side of the team and the sporting (guys who run the car) side of the team differing. From a design standpoint larger fuel tanks also take up more space, which creates headaches for packaging and at the very least is not positive for aero.

ENGINE TUNER
ENGINE TUNER
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Joined: Tue Nov 29, 2016 5:07 pm

### Re: Why do we have a fuel allowance and a max fuel flow rate?

The max race fuel limit is for 1 reason, to stop the teams from using fuel simply to create electrical energy.