Could Audi have raced with Biodiesel in Sebring 07?

[fernandes37]

Hello everybody,

I know the title might seem to be pure speculation. In fact it is, since the only thing I'm trying to get is a good answer to a slightly bizarre event.

Last weekend I watched the entire Sebring 12h race on Motors TV. That I was able to see (and please correct me if I'm wrong) neither of both Audi's were able to complete more than 27 laps per stint and throughout most of the race the usual was no more than 26, even at the end of the 9th hour when they were "under some pressure" by the XM Acura car.

In 2006 the Audi was, on average, capable of doing 33 laps per stint and one of the drivers, in one of the "yellow flag" free periods did 35 laps (from laps 271 to 305, in 2006).

Now, we all know that the fuel tank was reduced from 90L to 81L. This is a 10% fuel capacity reduction. If the same had happened to the number of laps per stint we would still get around 30 laps. But the fact is that Audi didn't! not one single time did the R10 even get 28 laps (excluding maybe pace car periods).

So, what happened to 3/4 laps per stint? In Sebring that's 20km per fuel tank, and that's about 12-14% of the range of the entire fuel tank. This might seem small but it is not. During this week I've searched for numerous possibilities. Some of them were eliminated from the onset:

1- I doubt that the car is heavier in 07 (if I recall correctly the R10 weight in Sebring 06 was 936kg, as Audi was not able to achieve minimum weight); in fact the evolution of the car from 06 to 07 should have made it lighter (if someone has data from the official weighting please give me some feedback).

2-Sebring 07 was in fact a race with an higher average speed than in 06. That can easily be seen comparing the 364 laps of 07 with the 349 laps of 06, but a more detailed calculation including time lost in the pit, plus yellow flag periods and race incidents (in 07, the winning car had a flat tyre while in 06 it lost 7 minutes in just one stop in the pits for repairs and checks) yields an interesting comparison. The average "on track" lap of the winning Audi in 07 was around 1:49 versus 1:52'9 for 06. This is a full 3% difference but it is not nearly enough to explain the gap.

3-Is the asphalt in Sebring new for 2007? This might explain some higher friction coefficient between tyre and road, accounting for an increase in fuel consumption...

4 - the aerodynamic factor is very relevant but unfortunately it is not my favorite engineering area. What I can say is that the overall aerodynamic efficiency should have improved the downforce to drag ratio of the 06 car, also explaining the 1% gain in the qualifying time. Still, once again, this fact on its own is not nearly enough to explain the gap.

5- the engine efficiency could be worse. Now, this is my engineering area and I most certainly doubt that this would ever be the case. If anything a new engine map for Sebring 07 should be available from the experience gained in Sebring 06 but also from the various events in which the R10 participated in 06, including the incredible fuel efficiency displayed in Laguna Seca 06. The engine was probably the part in which most weight gain should have been accomplished, reducing internal friction and hence consumption. Even more important, the optimization of cooling (difficult in a diesel since the lower exhaust temperature means that less heat exits the engine in this way, and more must be taken out through convection and radiation) should have yielded some aero gains. I have a very hard time imagining that engine efficiency did not improve.

Still the fact remains: 3 laps (at least!) have vanished somewhere. In order to have an idea what we are talking about, another stat is given here. During the 2nd/3rd hour of 06 Le Mans race Tom Kristensen twice made a 16 laps stint at an average time per lap around 3:44. This yields a 40-41L/100km fuel consumption allowing a 1lap fuel tank reserve. And this was achieved for an average speed of 218km/h. Sebring has more curves and hence an average speed of 202km/h, inferior to Le Mans. It is true that a larger part of the circuit is done at part throttle but then again the diesel (even a competition one) suffers much less from part throttle situations than a gasoline powered car. So how come does a similar calculation yield 48-49L/100km for Sebring 07? If we take 35 laps for Sebring 06 we achieve 41L/100km and if we do the same calculation with 33 we have 43L/100km.


In fact from my point of view only one explanation fits this scenario: could Audi be using Biodiesel in Sebring?
This question is really an open question because I do not know if it would be allowed. The thing is that Peugeot has already announced the intention to use it in Le Mans 2008. Now, I know Audi well enough to think that if they had a chance to beat Peugeot to this they would do it. Germany (and the rest of Europe for that matter) is currently undergoing a major discussion on CO2 emissions and to win an international competition with a biofuel would be absolutelly fantastic from a MArketing point of view. And we all know how Audi loves marketing.

Now, from an engineering point of view could it be done? Yes, Biodiesel (RME) has an energy value of around 37000-38000kj/kg meaning that a car will experience a 10-12% fuel consumption increase (required to maintain the same energy produced, because the difference in density is very small 842g/litre for diesel and 875g/litre for biodiesel), especially since biodiesel brings no efficiency gains on its own. This in addition to the 9 litres lost in the fuel tank could explain a 7 lap reduction (from 33 to 26) per stint.

All the rest can be easilly changed for Biodiesel (in Germany the 3 major manufacturers actually provide the option of using 100% Biodiesel as an everyday fuel and in VW it is an extra costing less than 200euros). This fuel consumption would account for the 3/4 laps lost per stint.

Still a problem is adrift. To my knowledge no currently production diesel engine is able to cope with 100% biodiesel (though I stand to be corrected once again) while equipped with a Diesel Particle Filter. And the Audi R10 is eqquipped with 2! Could this be the key to explaining the huge clouds of white smoke coming from the DPF each time the audi accelerated away from the pits?

Ok, this was a very long comment, maybe too long! I would love to hear the opinions of all of you into this subject. It is quite possible that my mind just wandered way too much into the 12h of Sebring 07!

Nuno Fernandes

[AU N EGL]

Fuels are SET by the ACO and IMSA. Bio fuels have not been approved as of yet with out special consideration.

answer too your questions

2, 3, and 4. Mich has better tires this year, which accounts for better times, let alone slightly better aero and engine efficacy

Rember as the sun goes down, track temps go down too. Teams switch to harder compounds too allow longer stints.

It will be interesting too see if the ACO will allow Pug to use any fuel other then the OFFICAL FUEL, which is Shell.

[TheNewBob]

Interesting idea but would it maybe need more concrete proof? The conspiracy theorist in me would suggest some Audi sandbagging, to aid their complaints of P2 being too quick in the ALMS?

I guess we'll see how many laps they can manage at LM - when P1 entries are much bigger.

[Hammerdown]

I'm with NewBob on this one. I think Audi are just trying to substantiate their whining about the rules. I too stand to be corrected, and hopefully we will get a clearer picture at LeMans, but judging by the current pace of the Pug, they won't be pushing Audi too hard. I'm afraid I don't trust anything Audi says anymore, which is a sad state of affairs, but brought on entirely by themselves.

[gwyllion]

Last year Audi used a very special gas to liquid diesel fuel. Perhaps this year the supplied diesel was more regular, hence higher consumption...

[broadrun96]

Originally Posted by gwyllion

Last year Audi used a very special gas to liquid diesel fuel. Perhaps this year the supplied diesel was more regular, hence higher consumption...

didnt they use that fuel only at LM as shell developed it and is their (ACO) official fuel, i think. but im more inclined to believe that audi was sandbagging to make thier case to IMSA. and if IMSA is smart they will call audi's bluff and tell them to deal with it or not drive the competition off the track. Guessing with the tighter smaller track this weekend, it could lead to a P2 win and then audi might actually leave, but sorry dr ulrich the TEAM didnt look all that challenged on the track when they actually pushed it and pulled away from the acuras like they were standing still.

[AU N EGL]

Originally Posted by broadrun96

didnt they use that fuel only at LM as shell developed it and is their (ACO) official fuel, i think. but im more inclined to believe that audi was sandbagging to make thier case to IMSA. and if IMSA is smart they will call audi's bluff and tell them to deal with it or not drive the competition off the track. Guessing with the tighter smaller track this weekend, it could lead to a P2 win and then audi might actually leave, but sorry dr ulrich the TEAM didnt look all that challenged on the track when they actually pushed it and pulled away from the acuras like they were standing still.

Yes I agree here.

[Bob Riebe]

As this is about Bio-diesel; would it not be financially sound if one of the large fast-food joints, McDonalds, etc., would contract with a team or company to take the thousands of gallons of used french fry oil, and re-cook it into diesel fuel, and sponsor a car on the race track, which would not only be sponsord by McDonalds but powered by McDonalds?

Bob