A Diesel Wins at Le Mans

[PJGD]

Well, it looks like my original question from thread108-64541 has been answered; An Audi R10 car with a V12 5.5L turbo diesel convincingly won the 2006 Le Mans 24 hour race:

http://www.lemans.org/24heuresdumans/live/pages/chronos_gb.html

The second team car had a number of problems, and came in third. Now the question is: how many other racing classes will diesels be competitive in? I note that PSA are preparing a V12 diesel to compete with the Audi, and now JCB are preparing a diesel world land speed record car using their 4.4L industrial diesel engine!

PJGD

 

[GregLocock]

You should be aware that the rules were modified to favour diesels.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[SomptingGuy]

If I remember rightly it's all down to the amount of fuel energy you are allowed to carry around with you. And the relative densities and calorific values are biased towards diesels.

I must admit I've always found mixed-rules racing a little difficult to take seriously. The rule makers try to jiggle with details in the rules to level the playing field, but there's always one clear best package. Take the dominance of Ducati in the 90s WSB. They had a bigger engine and less weight. And the two strokes in MotoGP when engines had to be the same size (500cc).

 

[Fabrico]

Special rules are just as often made for marketing, smog, and popularity as they are to level the playing field.

2-strokes really got hammered for marketing and smog. They have to race against 4's nearly twice their size.

 

[SomptingGuy]

"They have to race against 4's nearly twice their size."

These days yes, in the 80'2/90's no. And that reinforces my point (and Greg's). In a mixed field the winners are determined by the rules. Remember the oval piston "v8" NR500 that Honda made to try to get even with the strokers?

 

[PJGD]

Surely it is a case that the rules have changed to favour fuel efficiency, which is (or should be) an issue of abiding interest to society as a whole, including motor sports. It just so happens that the ascendancy of the diesel engine is for obvious reasons coinciding with this interest. I don't believe that the rules were changed to specifically favour the diesel cars per se.

I am not familiar with the specifics of the rule change, but any views on how significant it was to this race? Who would have won if the rules had not been changed, and by how much?

PJGD

 

[SomptingGuy]

"fuel efficiency"

These cars are going around in circles! Their efficiency in real-world terms is zero.

 

[crysta1c1ear]

I don't believe that the rules were changed to specifically favour the diesel cars per se.

I don't know what the rules are now or what they were in the past, but a quick look at the website gave me this file.

http://www.lemans.org/sport/sport/reglements/ressources/auto_2006/Regl_2006_prototype_ACO_fr_gb.pdf

Just glancing at a couple of sections (and maybe taking them out of context) gives me the impression you could race say (examples)

a 4 litre gasoline engine with more than two valves per cylinder and about 1/2 an atmosphere of boost,

or

a 5 1/2 litre diesel engine with nearly 2 atmospheres of boost.

 

[SomptingGuy]

Expanding on my earlier point...

The rules also state that the fuel tank must be no more than 90l in size, regardless of what's in it. Gasoline and diesel have similar lower heats of combustion based on mass (within 1%), but diesel is about 11% denser. So a full tank of diesel contains slightly more than 10% more energy than a full tank of gasoline. That's a bit of a head start in endurance racing - at least 10% less pit stops.

 

[PJGD]

OK, on the face of it, the new rules would appear to favour a diesel engine but how do you arrive at a fair equivalence formula, if that is an objective? In an SI world, it is horsepower that wins races, hence the inordinate focus on that parameter. In this case, the rules seem to have arrived at a near equivalency on horsepower since both the Judd and the Audi claim somewhere around 630 HP, and I believe that the Judd is naturally aspirated, so not taking advantage of the boost regulation.

The Judd has a rated speed of about 8K vs 5K rev/min for the Audi.

As for fuel efficiency, well yes, the Judd had to make 29 fueling stops as against 25 for the winning Audi. Obviously, the fewer the stops, the better.

PJGD

 

[Ataloss]

If they allow larger diesel engines with more boost to make the HP equivalent to gasoline engines, then they should shrink the size of the gas tanks on the diesel cars to force them to have the same number of pit stops as the gasoline cars. Why equalize one parameter if you're going to leave another very important parameter with a huge disparity?

Another rule exception the Audis got was that they were allowed a larger diameter restrictor (38mm for diesel vs 33 for gasoline) on their fuel filling rig because diesel flows slower than gasoline, and the ACO didn't think they should have slower pit stops than everyone else just because they're using a different fuel.

Granted, this is the first year for a diesel endurance racer so the ACO can't be expected to have the rules perfect yet to equalize the competition, but it certainly seems like they tried to give plenty of help to diesels to make up for their shortfalls, but didn't give them any restrictions to lessen their natural advantages.

Bob

 

[PJGD]

What is the issue with multiple sets of rules (other than in the short term)? Is it not the case that where there are multiple rule sets, the competitors will migrate to the rules that consistently deliver the winner, so that it quickly becomes in effect a single set? In this way the organizers leave the door open for the sort of innovation that you would not get if it were a single set from the start.

PJGD