Le Mans limits only the volume of the fuel tank. Diesel has ~13% more energy by volume so that means you can do ~16 laps on one tank vs. ~14 on gasoline. Fewer pit stops gives you a huge advantage in endurance racing. Note that the greater efficiency of the diesel engine in part load matters little when you spend 70% of the time at full throttle.

That said, hats off once again to Audi. Their four-lap winning margin was more than due to the fuel advantage alone. They have a world-class engineering and race team that has now earned its stripes in Le Mans seven years running. Perhaps the hardest part was delivering a lightweight diesel engine that could take advantage of the higher fuel density, and a gearbox that could cope with the stupendous 1100 Nm of torque. The R10 has a 650hp V12 with an aluminium crankcase - production diesels all feature cast iron blocks. Peak rated RPM is ~5,500 vs. ~4,500 in a production diesel. It helps if you have an oil major custom-tailoring your fuel for you (GTL has a high cetane number).

Sports cars are the only vehicle segment that had hitherto not featured diesel engines, because customers perceived the combination as an oxymoron. With this win under their belt, it's probably safe to say that Audi will want to offer a diesel in a future sports car. Here's what it might look like:

http://www.autotrend.com/Audi_LeMans_Quattro.html

Regenerative braking requires someplace to store the energy to, and then another system to get it back. Batteries store less energy per pound than diesel contains, and the electric motor and support system (including gear box) is more added weight. There's a reason they went with an aluminum block.

but not to forget that diesel is ~15% heavier then gasoline.

A properly designed and built, Diesel-Hybrid could easily win next years Le Mans.

You would be able to change the batteries after every race so you could really go for the most advanced chemistries for fast recharging and lightweight. All this would be worthless for street use (the battery portion...though efficient controllers and motors could carry over).

While such batteries might be worthless for street use, some important chemistry and stress test could be covered by motor sport's aggressive R&D.

They could start off light - maybe a 50 hp motor/generator with a small supercap. That shouldn't weigh much..?

Why batteries? Why not ultra caps?

Le Mans limits only the volume of the fuel tank. Diesel has ~13% more energy by volume so that means you can do ~16 laps on one tank vs. ~14 on gasoline. Fewer pit stops gives you a huge advantage in endurance racing.
So why is this the first diesel to win Le Mans? It is still an achievement, no matter how you look at it.

If my memory is not all that bad, there was a a biodiesel car racing at Le Mans a few years back (Team Nasamax). It would be interesting to see if this achievement (the R10 winning Le Mans) would spur a bit more interest in that technology again.

I'm taking a stab here but given the forum I'm sure someone will correct me if I'm wrong. Isn't this the first race car at anywhere near this level of competition to incorporate emission controls? I can't imagine that they have been a high priority on other projects. Also does anyone know how much of a power hit the particulate filters might have on the final HP and Torque numbers?