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One week before Le Mans, Audi lifted the veil on how the technology it is using in racing is also beneficial to production cars.
Audi said that 15 years of engine development have been shaping Audi’s Le Mans prototype racing commitment. Through intensive development work the engineers have repeatedly compensated for the restrictions imposed by the regulations while consistently 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.
The Le Mans project began with a 3.6-liter gasoline engine that delivered around 544 horsepower(hp); this was raised to 610 hp only a year later.
A major stride achieved in 2001 was TFSI gasoline direct injection being used for the first time. It significantly reduced fuel consumption while drivability and response behaviour substantially 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.
Five years later, Audi celebrated an achievement with the TDI engine at Le Mans, introducing diesel to its racing cars.
The brand immediately clinched the first victory of a diesel-powered sports car at Le Mans in 2006. Out of 5.5 liters of displacement, the V12 engine of the Audi R10 TDI developed more than 650 hp. This was the first Audi diesel engine with an aluminum cylinder block.
Audi said its diesel engine development directly benefited 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 maximum specific performance and best 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 allowed combustion and power output to be optimized, 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.
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. Audi said that VTG technology clearly improves response behavior. In 2010, Audi with the R15 TDI not only celebrated victory at Le Mans but, after completion of 397 laps and 5,410 kilometers, broke the absolute distance record, which had existed for 39 years.
The most incisive change, as well as a major technical achievement by the Audi motorsport engineers, 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 liters.
Audi said it developed a V6 TDI engine packed with innovations. 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.
The Audi engineers respond to ever more limitations by making continuous progress, according to the company. 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 650 hp to around 490 hp 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 liter of displacement went up from 118 hp in 2006 to 146 hp 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 54 hp to an 90 hp, in other words by 65 percent.
Even more impressive is the development of fuel consumption.
Audi has improved fuel 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 liter has clearly increased.