Dr. Diesel would be proud: Audi hopes its V12 TDI race engine will advance the state of the art for production engines, and continue the company's domination of endurance racing.

A bar in Ingolstadt, Germany, is not where you would expect the future of sports prototype racing to change, but it is where Dr. Ulrich Baretsky, head of Engine Technology at Audi Sport, sat down one night in January 2003 with a representative of the ACO (Automobile Club de l'Ouest, the sanctioning body for the Le Mans 24 Hours) to discuss endurance racing's future. "During this conversation, we realized that 50% of the cars on the market in Europe were diesels. So why not race a diesel engine?" recalls Baretsky. The one problem was that Baretsky and his team were satisfied with the direct-injection gasoline race engine in the Audi R8, and they really didn't want to change. That's when--like the apostle Paul in the New Testament, as he puts it--lightning struck. "Why not do it?" he asked.

After VW Group chairman Ferdinand Piech gave his blessings at Le Mans in 2004, the first diesel race engine was running on the dyno in early May 2005. "One of our targets was to make an engine that would give diesel technology a real push." The aluminum-silicon alloy used in Audi's production gasoline engines (its production diesels use vermicular cast iron) is used in the block and heads of the 90[degrees] V12 TDI. Baretsky won't divulge any secrets about the motor, except to say there are some "clever solutions found in Audi engines many years ago," and that this technology could be applied to road engines in the future. Though relatively compact for a 5.5-liter V12, the block is heavily cross-braced, and engine masses are concentrated down low. This gives a greater area through which the diesel's high combustion forces can be dissipated. The twin-turbo engine runs an absolute boost pressure of 2.94 bar.

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"Compared to other diesels," he says, "the V12 is light--very light--and I am sure this weight will fall as we go forward." How light is light? Again, Baretsky is coy, but he does admit that the weight per cylinder is the same as the 3.6-liter FSI V8 of the Audi R8 that preceded it. What is lighter, however, is the five-speed X-Trac gearbox. Though the massive 1,100 Nm (approximately 810 lb-ft) of torque produced by the 650-hp V12 lets the team stretch out the gear ratios somewhat, the bigger gears and shafts necessary to handle this torque would suggest the gearbox weight should be similar to the R8's six-speed transmission, not less.

Despite early rumors that the R10's engine would spin to a heady--for a diesel--8,000 rpm, Baretsky insists the engine's power band lies between 3,000 and 5,000 rpm, and the rev limit is not much beyond this. The Bosch-supplied common-rail injector system looks outwardly similar to a production motor's, but runs to much higher pressures. "Our production car target over the next three years is to raise injector pressures to 2,000 bar," says Baretsky, "but we are already there with the V12." This suggests that Audi and Bosch are planning to fit hydraulically assisted injectors in place of the piezo units used today as the project develops.

Particulate traps are fitted aft in the chassis at the end of the exhaust pipes. This is not the ideal location for weight distribution, especially in terms of the chassis' polar moment of inertia. Says Baretsky: "We'd be happier to have them closer to the engine, but this would have put them in the middle of the rear axle." Again, the composition of the filters is secret, though he did admit the design is a new technology from Dow that is lighter than a typical particulate filter used today.

The engine control unit (ECU) is not a repurposed production unit, but one with software specifically written for this application. "There are 12,000 to 14,000 different labels you can address in a road car ECU, and functions for which we have no use," says Baretsky. "If you took out one, it would affect all of the others. It's better to start from scratch." Unlike a road car ECU, the race version has a pit lane speed limiter and a start function that keeps engine rpm up when exiting the pit lane so the engine does not stall. Asked if he might at least borrow the road car's traction control, Baretsky admits that the R10--like its R8 predecessor--does not have this function, though--since the regulations allow it--a tailor-made utility will be added to the software package. Asked how they keep the tires from wearing prematurely, especially in light of the available torque, Baretsky replies: "Good drivers!"

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Another item on the jovial engineer's to-do list is a sound system for those drivers. It's not your typical car audio system, but a speaker system for the driver's helmet that lets him hear the engine note as the vehicle speed rises. "Tom Kristensen [one of Audi's lead drivers] told me they missed the information they gain from the engine noise," says Baretsky. He estimates the R10 at full-throttle puts out about 104 dB, or about 4 dB less than the R8.

As the program moves forward, Baretsky expects it to greatly improve Audi's diesel simulation capabilities ("Those tools came to their limits quite quickly because the boundaries we set for this project passed the normal ranges in terms of combustion pressures and things like that," he admits.), and push the knowledge base in unknown directions. "I'm not a prophet," he admits, "but I would dare to say the diesel world will have changed significantly--I expect a bigger push than gasoline technology has gotten over the past 60 years--in ways that benefit us all. As more competitors join us at the track, this knowledge will grow."--CAS

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RELATED ARTICLE: A Diesel for Privateers

Audi is in. Peugeot says it will be next. Other manufacturers are certain to follow their lead and build diesel engines for endurance racing. Where does this leave the privateer? If you listen to Dave Morrison, the business operations manager for Ricardo Motorsport, and Russ Wakeman, technical director at Ricardo's Detroit Technology Campus (www.ricardo.com), running a race team without factory support doesn't mean you have to do without the latest technology.

"If you are willing to relax the cylinder pressures a bit," says Morrison, "then you limit the Pmax [the maximum in-cylinder pressure] to 130 to 140 bar and get a much lighter engine." This reduces the fuel economy below what a diesel running higher pressures would see, but makes the structure less critical in the overall design. In fact, it is possible to take a racing gasoline engine and convert it to run as a diesel, which is what Ricardo has done. They started with a standard 5.0-liter version of the Judd GV5 V10, changed the top end (heads, port shapes, valve sizes, fuel injection system, replacing the spark plugs with injectors), and added a pair of turbochargers. "We had to change the fuel pump to one that could handle diesel and produce 1,600 bar in the common rail system," says Morrison. To which Wakeman adds: "The combustion is completely different, but--beyond getting a spark plug out and a compact injector in--that's about the level of redesign needed." As such, they expect the Ricardo-Judd diesel to be very cost effective when compared to Audi's V12. If they can find a team willing to finance the project, the engine should be ready for testing in a chassis this fall.