One more week before Audi will be competing at the classic 24-hour race at Le Mans for the 15th time. On the 90th anniversary of arguably the world’s most important endurance race, the challenge is particularly great for the brand with the four rings, following the most recent changes in the regulations.

Le Mans 2013 will be a year of historic dimensions. The inaugural event of the endurance race was held 90 years ago. Audi is now competing for the 15th time. The current World Endurance Champions Marcel Fässler/André Lotterer/Benoît Tréluyer (CH/D/F) will enter the race in the number ‘1’ Audi R18 e-tron quattro. If successful, the three drivers, following two consecutive victories, could manage a hat-trick at La Sarthe. This was last achieved by another Audi trio: In 2000, 2001 and 2002, Frank Biela/Emanuele Pirro/Tom Kristensen (D/I/DK) remained unbeaten three times in succession.

This report, the third in our triad, reviews 15 years of engine development that have been shaping Audi’s prototype racing commitment. Through development work the engineers have repeatedly compensated for the restrictions imposed by the regulations while enhancing efficiency of the engines fielded.

Two major eras have shaped Audi’s commitment at Le Mans from the perspective of Ulrich Baretzky, Head of Engine Development at Audi Sport: Until 2005, gasoline engines powered Audi’s LMP race cars, since 2006 the engines have been diesel units. For Audi, this is linked to numerous innovations.

Audi’s 1st LMP sports car was propelled by a V8 twin turbo engine

The Le Mans project began with a 3.6-litre gasoline engine that delivered around 400 kW (544bhp), and over 449 kW (610bhp) a year later. A development which took place in 2001 was TFSI gasoline direct injection being used for the first time. It reduced fuel consumption while drivability and response behaviour improved. At the pit stops, the time for starting was shortened by up to 1.3 seconds because the directly injected fuel was burned more directly. The Audi team transferred the technology that was tested in racing into production cars when the first models with FSI and TFSI engines delivering fuel economy benefits of up to 15 percent were launched.

Audi’s V12 Diesel engine for Le Mans

Five years later, Audi celebrated a new achievement with the TDI engine at Le Mans. After Audi, as the inventor of the TDI, had offered its first production model with this technology in 1989, the brand immediately clinched the first victory of a diesel-powered sports car at Le Mans in 2006. From 5.5 litres of displacement, the V12 engine of the Audi R10 TDI developed more than 478 kW (650bhp) along with torque of over 1,100 Nm. This was the first Audi diesel engine with an aluminium cylinder block.

Audi’s diesel engine development directly benefitted from Le Mans technology. Experiences gained in pre-development were fed into the first racing pistons. The injection system with two high-pressure pumps and piezo injectors has been refined by Audi for improved performance and efficiency in racing. The injection pressures of the hydraulic system and the ignition pressures in the cylinder have continually been increasing to this day. This way, combustion and power output could be optimised, which has been beneficial to production development as well. Today, injection pressures of 2,800 bar are achieved in racing and 2,000 bar in production cars.

Double-flow design turbocharger with VTG technology

Variable turbine geometry (VTG), which has long been in standard use in volume production, was introduced into racing by Audi in the V10 TDI in 2009, following several years of development. The biggest challenge was posed by the high temperatures of over 1,000 degrees centigrade. VTG technology improves response behaviour.

The 2009 V10 TDI engine was the 2nd generation of diesel engines

The Audi R15 TDI was powered by a V10 TDI engine

In 2010, Audi with the R15 TDI not only celebrated victory at Le Mans but, after completion of 397 laps and 5,410 kilometres, broke the absolute distance record, which had existed for 39 years.

The current V6 TDI engine for Le Mans

The most incisive change was brought about by the engine regulations for 2011. For diesel engines, the regulations forced the engineers to reduce the volume by 1.8 to 3.7 litres. Audi developed a V6 TDI engine with new features. The exhaust side is located inside the V with its 120-degree angle (‘hot side inside’). A double-flow mono-turbocharger is fed with the exhaust gas from both banks and its compressor is of a double-flow design as well.

Audi engineers continued to respond to ever more limitations by making more design improvements. For example, the diameter of the air restrictor in the diesel era since 2006 was reduced by 34 percent. Boost pressure decreased by 4.7 percent and cubic capacity by almost 33 percent. Absolute output dropped from over 478 kW (650bhp) to around 360 kW (490bhp) today, in other words by 24 percent. Considering this, the increases achieved with respect to specific outputs are particularly noteworthy. For instance, the engine output per litre of displacement went up from 87 kW (118bhp) in 2006 to 107 kW (146bhp) in 2011 – a gain of nearly 24 percent. The piston area output – which is the measure for the output delivered by each individual cylinder – during this period of time grew from 40 kW (54bhp) to 66 kW (90bhp), in other words by 65 percent. Even more interesting is the development of fuel consumption. Audi has improved consumption per lap in racing operations at Le Mans from the first to the most recent generation of diesel engines by more than 20 percent, while the engine’s output per litre has clearly increased.

Source: Audi

Tags: André Lotterer, Audi, Audi R10 TDI, Audi R18 e-tron quattro, Audi Sport, Benoît Tréluyer, Emanuele Pirro, engine design, Frank Biela, Le Mans 24 Hours, Marcel Fässler, motorsport, racing, TDI engine, Tom Kristensen, Ulrich Baretzky, V12, variable turbine geometry, VTG