The V12 TDI diesel engine, which will propel the Audi R10 in the 2006 Le Mans 24 Hours, marks many motor racing 'firsts' - and breaks new engineering ground.
The totally new powerplant has a cubic capacity of 5.5 litres - the maximum permitted at Le Mans - sending Audi into previously unexplored diesel-engine terrain with power exceeding 650 hp and a massive torque of more than 1100 Newton metres.
"This engine is the specifically (for its size) most powerful diesel there is in the world and, up until now, the biggest challenge that Audi Sport has ever faced in its long history," explained Ulrich Baretzky, head of engine technology at Audi Sport. "There has never been anything remotely comparable. We started development with a clean sheet of paper."
The V12 TDI used in the R10 is the first Audi diesel engine with an aluminium crank case. The cylinder-bank angle is 90 degrees, while the engine has four valves per cylinder and twin overhead camshafts.
The fuel induction is made by a modern "Common Rail System". The injection pressure easily exceeds the 1600 bar achieved in production cars, while the ignition pressures also reach values never previously seen in any Audi engine.
The turbo pressure produced by the two Garrett turbochargers is limited by the regulations to 2.94 bars (absolute), while the diameter of both engine air intake restrictors is also restricted, to 2 x 39.9 millimetres.
The engine's power and the high torque are available to the driver practically from idling speed - a characteristic of diesel technology - with the usable power band between 3000 and 5000 revs per minute, much lower than racing petrol engines.
Something else unfamiliar to the drivers will be the low noise level and, unique for a racing engine, the smooth running of the engine. At high speeds the 650 hp engine can not be heard from the Audi R10 prototype's "open" cockpit while there is hardly any vibration.
On the outside, the twelve-cylinder produces a faint, but deep sound that some would struggle to identify as a diesel. Indeed, the new R10 can only be recognised acoustically as a diesel-powered sportscar during the warming-up process or in the pit lane.
There are also no visual signs that a diesel power unit is at work in the back of the R10, which will be equipped with a pair of diesel particle filters for the 24 Hours of Le Mans. However, flashes of flame from the exhaust, which are created by unburned petrol in spark-ignition engines, will not be seen coming from the R10.
One of the diesel engine's biggest advantages is the low fuel consumption, especially at part-throttle and overrun. However, when compared to more classic circuits which demand a higher ratio of part throttle, the lower specific consumption will hardly be noticeable at Le Mans because the quota of full-throttle is almost 75 percent.
The enormous torque of over 1100 Newton metres posed previously unforeseen demands in the development of the R10 drive train - with the forces acting on the transmission system even greater than those experienced by a
Formula 1 racing car.
The use of traction control (ASR) reduces the high loads created by the torque fed to the rear tyres, and helps the driver to modulate the V12 TDI engine's power delivery, particularly in wet conditions, which represents a new dimension even for seasoned campaigners.
"It's impressive just how the engine keeps on pushing even in the high gears," said three-time Le Mans winner Frank Biela, who was at the wheel of the R10 during the roll-out at the end of November.
Inside the V12 TDI, the extremely high pressures in particular create forces never seen before in a racing engine. However, the main target of the Audi technicians is still to reach the reliability level of the R8, which never recorded a single engine failure in the 77 races it has contested to date.
