In 2006, Audi made history at Le Man by becoming the first manufacturer to win the world's toughest endurance race with diesel power. This year marks the anniversary of this achievement and the TDI engine is more efficient than ever before, so much so that the Audi R18 is the most powerful and fuel efficient Audi LMP1 race car.
The "higher-further-faster" of TDI power was heralded ten years ago with a sound that even seasoned campaigners weren't used to. The Audi R10 TDI raced so quietly that the sound was almost undetectable. "At high speed, even the wind noise was louder than that of the engine," recalled Le Mans legend Tom Kristensen who leads the all-time winners' list of the 24-hour race with nine wins. Driving and shifting according to sound level was no longer the norm in the LMP1 race car.
In preparation for the 2006 season Audi Sport had to master one of its greatest challenges. A V12 TDI engine not only meant a new powertrain: We had to come up with a new concept for the entire race car,” says Head of Audi Motorsport Dr Wolfgang Ullrich. “From the proportions of the race car and its weight distribution to airflow, the cooling air requirement and power transmission, everything was new, as torque and output surpassed anything we’d previously known.”
Audi Sport tested their diesel engine for Le Mans with Audi AG's pre-production and production development. The 5.5 litre twelve cylinder unit for use in racing was the first Audi diesel engine with an aluminium cylinder block and the Audi R10 TDI completed its initial rollout on the Italian race track at Misano on 29 November 2005. Just 200 days later it competed in and won the Le Mans 24 Hours. In between, 30,000 test kilometres, plus another 1,500 hours of testing the V12 TDI engine on dynamometers, were clocked up. Frank Biela/Emanuele Pirro/Marco Werner (D/I/D) crossed the finish line after 380 laps as the winners having covered 5,187 kilometres in the process. The TDI engine from Ingolstadt and Neckarsulm came out on top the next two years against fierce competition from other diesel powered vehicles.
Audi achieved the next step with the R15 TDI in 2010. The twelve cylinder unit that had previously been used was replaced with a V10 TDI engine which was 100mm shorter, 10% lighter and powered the open-cockpit sports car to a new top performance. Timo Bernhard/Romain Dumas/Mike Rockenfeller (D/F/D) covered 5,410.713 kilometres in 397 laps at Le Mans, breaking a 39 year old record from an era when no chicanes slowed the pace on the Hunaudières straight. The R15 TDI achieved a one-two-three win and, for the first time, its 5.5 litre V10 TDI used two turbochargers with variable turbine geometry (VTG) which improved the engine's responsiveness.
A new era arrived in 2011 with the production of the Audi R18 TDI which boasted an innovative, compact and very efficient V6 TDI engine. Engine displacement decreased by 1.8 to 3.7 litres, meaning consumption was reduced and production relevance was increased. The cylinder banks with a 120-degree angle enclosed the exhaust side – in other words, the exhaust manifolds were inside the V configuration as well. A single double-flow turbocharger was fed by the exhaust of both banks and its compressor was of a double-flow design as well and directed the fresh air through two intercoolers into the intake manifolds on the outside. The diameter of the air restrictor decreased by 34% since 2006 in addition to charge pressure being reduced by 4.7% and the cubic capacity also decreasing by almost 33%. Power output also dropped from more than 650hp to 490hp, which equates to 24%. As a result of this decrease, output per litre increased from 118hp in 2006 to 146hp in 2011, which also equates to almost 24%. The higher injection pressures of the racing injectors lead to more efficient combustion. Now operating at 3,000 bar the racing engine was a precursor of the rising pressures making their way into the automobile.
Marcel Fässler/André Lotterer/Benoît Tréluyer (CH/D/F) won in 2011 with the R18 TDI and a year later with the R18 e-tron quattro that used a hybrid powertrain for the first time. In 2013, Loïc Duval/Tom Kristensen/Allan McNish (F/DK/GB) were victorious at Le Mans with a further developed version of the R18 e-tron quattro. Following Fässler/Lotterer/Tréluyer in 2012, they were the next title winners in the 2013 FIA World Endurance Championship (WEC). Efficiency regulations were introduced in 2014 and marked a significant change in racing. Beforehand, output was limited by factors such as air restriction or cubic capacity, whereas it now applied purely to energy. Audi's V6 TDI engine was enlarged and had to make to with around 22% less fuel that its predecessor to four litres of displacement. This was also the year that Fässler/Lotterer/Tréluyer achieved their third victory, the eighth for the TDI engine at Le Mans.
In the most recent 2016 season, the regulations have reduced energy consumption once again however Audi has developed the V6 TDI engine to a new level once again. “We’re now using the engine concept for the sixth consecutive year. This shows how good the basic idea still is,” says Ulrich Baretzky, Head of Engine Development at Audi Sport. “Due to efficiency increases, we’re compensating for the lower amount of fuel to some extent.”
The current V6 TDI engine consumes 32.4% less fuel than the first generation from 2011, however the progress made in comparison to 2006 is even more substantial. Today the Audi LMP1 race car with the current powertrain use 46.4% less fuel at Le Mans than it did ten years earlier. Despite this, it can now achieve laptimes between 10 and 15 seconds better than those a decade ago. All this can be attributed to the individual strides that have been made, particularly in the areas of aerodynamics, lightweight design and powertrain.
Audi will be providing extensive reports on its Facebook (AudiSport) and Twitter (@audisport) channels. The brand’s fans can additionally watch on-board footage with telemetry data and further information at www.audi-motorsport.com.