Blown diffusers = blowing fuel

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Fred_C_Dobbs
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Blown diffusers = blowing fuel

Postby Fred_C_Dobbs »

When they began to talk of the odd exhaust note from the RB6s that was thought to be some engine tweak to maintain downforce when off throttle, you had to presume it meant added fuel consumption.

This is lifted from the Renault Sport preview of the Malaysian GP. Renault Sport supplies the RS27 lump to RBR, Team Lotus and Lotus Renault GP:


"Did you know...

The blown floors prevalent in the field this year mean that engine and exhaust management is even more crucial than in previous seasons. To power a blown floor effectively and generate additional downforce, an engine must produce significant amounts of exhaust gas. Simply put, the more fuel burned, the more exhaust is produced and potentially more downforce. Since the RS27's fuel consumption rate is extremely good, the Renault-equipped teams were able to burn 10% more fuel than normal during the Australian Grand Prix without running out of fuel, therefore giving more exhaust flow to its partners using the blown diffuser."
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Re: Blown diffusers = blowing fuel

Postby f1ea »

ouch....
so that means.. less fuel for Q also.... could that be about 1sec's worth of fuel?
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Re: Blown diffusers = blowing fuel

Postby What's Burning? »

^^ not really less fuel, I think what it means is that they can generate more exhaust with the same amount of fuel. If they load less fuel for Q then they won't be able to generate the same amount of blown exhaust, so the get only one benefit not both.
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Re: Blown diffusers = blowing fuel

Postby f1ea »

What's Burning? wrote:^^ not really less fuel, I think what it means is that they can generate more exhaust with the same amount of fuel. If they load less fuel for Q then they won't be able to generate the same amount of blown exhaust, so the get only one benefit not both.


If Mclaren need to burn 100 kg of fuel for a fast Q lap...
Wouldnt Red Bull be able to go with 90 kg of fuel for the same lap? running 90kg is faster.....
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Re: Blown diffusers = blowing fuel

Postby What's Burning? »

f1ea wrote:
What's Burning? wrote:^^ not really less fuel, I think what it means is that they can generate more exhaust with the same amount of fuel. If they load less fuel for Q then they won't be able to generate the same amount of blown exhaust, so the get only one benefit not both.


If Mclaren need to burn 100 kg of fuel for a fast Q lap...
Wouldnt Red Bull be able to go with 90 kg of fuel for the same lap? running 90kg is faster.....


No that's not the point of contention... you're claiming that they will put in less fuel because they are more efficient. But the OP is about burning more fuel with the engine timing in order to create more blow into the diffuser. So in order to be able to do that they need to have the additional fuel. Which would negate your weight savings equation. You can do one or the other, but not both.
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Re: Blown diffusers = blowing fuel

Postby f1ea »

What's Burning? wrote:No that's not the point of contention... you're claiming that they will put in less fuel because they are more efficient. But the OP is about burning more fuel with the engine timing in order to create more blow into the diffuser. So in order to be able to do that they need to have the additional fuel. Which would negate your weight savings equation. You can do one or the other, but not both.


who says they can't have both?

they can either:
1. run less fuel, for the same blown gasses = ligther car
2. run more fuel (equal to other teams), for more blown gasses = faster car
3. An optimum [mix between 1 and 2].... i'm sure they have graphs to figure out which is the fastest/optimum combo.
Last edited by f1ea on 07 Apr 11, 02:24, edited 1 time in total.
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Re: Blown diffusers = blowing fuel

Postby myownalias »

That's interesting and would explain the Renault powered cars pace; with the exception of Team Lotus. Being able to generate more downforce without needing to change the fuel mixture to finish the race is a big advantage. From my understanding; RB and Renault can run with a lower fuel load in qualifying for say three laps with full exhaust gasses to the blown floor to generate the additional downforce; the other teams would have to run an additional 10% more fuel to get the same effect; but the difference wouldn't be massive as 10% of 3 laps of fuel is only about a 1/3rd of a lap of additional fuel load, it would mean maybe 1 or 2 tenths of a second, yes it'll make a difference but it doesn't explain the 0.8 seconds Vettel had on Hamilton.
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Re: Blown diffusers = blowing fuel

Postby bud »

Other power plants could run the same blowing capacity in a race but would have to turn the mix down sooner to make it to the end. Renaults would have the advantage of a longer hard core blowing stint!
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Re: Blown diffusers = blowing fuel

Postby bigpat »

I'd take this announcement with a grain of salt....

Would you really openly reveal something like that?? Don't believe everything you read.

In F1, 10kg of fuel is worth approx 0.3 sec in lap time. That is a fair amount for the other manufacturers to be out by.....

To create more power, you must burn more fuel, simple. It is possible to use less fuel, if you make less power. Remember, the Renault is not considered the most powerful lump on the grid......... I think this needs to be remembered.

In Melbourne, the Renault engined cars had a distinct crackle and pop on over-run, the tell tale sign, of a lean fuel setting, so that statement baffles me even more.

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Re: Blown diffusers = blowing fuel

Postby myownalias »

bigpat wrote:In F1, 10kg of fuel is worth approx 0.3 sec in lap time. That is a fair amount for the other manufacturers to be out by.....

To create more power, you must burn more fuel, simple. It is possible to use less fuel, if you make less power. Remember, the Renault is not considered the most powerful lump on the grid......... I think this needs to be remembered.

But surely if the Renault engine is 10% less powerful; it would burn 10% less fuel so will allow it to run 10% more race distance at optimum fuel mixture. Red Bull have Adrian Newey on their side; his designs are probably worth more time than the deficit of the lesser powered Renault engine. I take everything I hear from F1 circles with a large pinch of salt but this is one of the more plausable things I have heard. Of course the amount of exhaust gases required to activate the blown floor will also depend on the exhaust design!

bigpat wrote:In Melbourne, the Renault engined cars had a distinct crackle and pop on over-run, the tell tale sign, of a lean fuel setting, so that statement baffles me even more.

I always thought the crackle and pop was a result of excess fuel being dumped on the exhaust?
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Re: Blown diffusers = blowing fuel

Postby bigpat »

myownalias wrote:
bigpat wrote:In F1, 10kg of fuel is worth approx 0.3 sec in lap time. That is a fair amount for the other manufacturers to be out by.....

To create more power, you must burn more fuel, simple. It is possible to use less fuel, if you make less power. Remember, the Renault is not considered the most powerful lump on the grid......... I think this needs to be remembered.

But surely if the Renault engine is 10% less powerful; it would burn 10% less fuel so will allow it to run 10% more race distance at optimum fuel mixture. Red Bull have Adrian Newey on their side; his designs are probably worth more time than the deficit of the lesser powered Renault engine. I take everything I hear from F1 circles with a large pinch of salt but this is one of the more plausable things I have heard. Of course the amount of exhaust gases required to activate the blown floor will also depend on the exhaust design!

bigpat wrote:In Melbourne, the Renault engined cars had a distinct crackle and pop on over-run, the tell tale sign, of a lean fuel setting, so that statement baffles me even more.

I always thought the crackle and pop was a result of excess fuel being dumped on the exhaust?


No , excess fuel in a naturally aspirated engine over-run, doesn't make any real sound, you just see the flames as the unburnt fuel ignites in the exhaust.
Running lean on overrun, also assists with engine braking. Sometimes you hear a pop, just as the driver touches the throttle, as the ECU tips in a excess amount of fuel, to re wet the wall of the inlet manifold, so the engine doesn't stumble as it comes under load.

Granted, if the Renault, makes less power, it will also use less fuel. But not 10%. I can't see the Renault engine being 75 HP down on the others...
Now matter how good Newey ( and his aero team) are, you can't overcome that power deficit, have competitive downforce, and still not be miles off the top speed of others. Remember in 2008, Red Bull were up up in arms when they thought the Renault engine was only 30 HP down...

I'm not doubting that the engine is more fuel efficient than the others, but 10% is a huge amount, in a grid where power difference is less than 5%. A fuel consumption advantage has to achieved hand in hand with the fuel supplier, something I doubt Shell, Mobil & Elf etc would be behind in fuel development. And it can't come from smarter electronics, as everyone uses the same ECU, with same capabilities. Just as much, having strictly controlled materials, and long life engines, I would be absolutely floored if one side could reduce frictional losses in a engine 10% compared to others. The cars would then have 10% smaller radiators, something Newey would be straight onto.....

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Re: Blown diffusers = blowing fuel

Postby Fred_C_Dobbs »

Burning fuel to gain downforce
On Red Bull RB7 At GP Australia

Once again Red Bull have devised another blown diffuser system, even after rules were made more strict. The team's car now makes use of the energized exhaust flow to separate the laminar flow of the rear wheels from the diffuser's airflow, hence creating a much more efficient diffuser and beam wing combination.

To make this work efficiently though, it is important that flow from the exhausts is more or less constant, or otherwise put, the car's behaviour will be more predictable when exhaust flow does not suddenly change. Therefore, Renault have been tuning its engine within the strict limits of the rules to optimise fuel burning, even when the throttle is lifted. While tuning details will be different for the forward exiting exhaust on the Lotus Renault, the same principle applies there as well.

The benefits are to such an extent that Renault have declared themselves: "Since the RS27’s fuel consumption rate is extremely good, the Renault-equipped teams were able to burn 10% more fuel than normal during the Australian Grand Prix without running out of fuel, therefore giving more exhaust flow to its partners using the blown diffuser."
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Re: Blown diffusers = blowing fuel

Postby acosmichippo »

So I was re-watching Practice two on BBC iPlayer just now, and around 29:10, the announcers made it sound like these Renault engines burn 10% MORE fuel in order to accomplish the greater exhaust flow during breaking, which makes a whole lot more sense.

So apparently in F1, 'more efficient' = MORE fuel use.
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Re: Blown diffusers = blowing fuel

Postby Fred_C_Dobbs »

acosmichippo wrote:So I was re-watching Practice two on BBC iPlayer just now, and around 29:10, the announcers made it sound like these Renault engines burn 10% MORE fuel in order to accomplish the greater exhaust flow during breaking, which makes a whole lot more sense.

So apparently in F1, 'more efficient' = MORE fuel use.

Magician though he may be, Newey has not created a perpetual motion machine, and the energy for that additional downforce has to be coming from somewhere.


(Hint: it's the fuel tank)
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Re: Blown diffusers = blowing fuel

Postby myownalias »

Fred_C_Dobbs wrote:
acosmichippo wrote:So I was re-watching Practice two on BBC iPlayer just now, and around 29:10, the announcers made it sound like these Renault engines burn 10% MORE fuel in order to accomplish the greater exhaust flow during breaking, which makes a whole lot more sense.

So apparently in F1, 'more efficient' = MORE fuel use.

Magician though he may be, Newey has not created a perpetual motion machine, and the energy for that additional downforce has to be coming from somewhere.

(Hint: it's the fuel tank)

Surely that's the whole point; 10% more fuel efficient engine means that Renault powered cars can have the same size fuel tank as everyone else and still be able to run optimum fuel mixture for 10% longer giving the blown floor full downforce unlike other teams that need to turn down the mixture or even have a larger fuel tank; which means more weight.

I guess we'll find out this weekend; if the Red Bulls streak away in the last 10% of the race; we'll know the answer!
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