One
week before the Le Mans 24 Hours race in France celebrates its 90th anniversary, it is worth noting that some 15 years
of engine development have been shaping Audi's 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-litre gasoline engine that delivered around 400 kW (544 bhp), but growing to over 449 kW (610 bhp) 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.
Some five years later, Audi
celebrated a pioneering achievement with the TDI diesel 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
(650 bhp). Particularly impressive was its torque of over 1,100 Nm. This was
the first Audi diesel engine with an aluminium cylinder block.
Diesel development benefits
Audi's diesel engine development directly benefited from
Le Mans technology. Experiences gained in pre-development were fed into the
first racing pistons. The fuel injection system with its two high-pressure
pumps and piezo injectors has been refined by Audi for maximum specific
performance and best efficiency in racing.
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| Audi Le Mans engine under development
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
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.
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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 clearly improves response behaviour.
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 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 litres.
In response, Audi 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. 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 (650 bhp) to around 360 kW
(490 bhp) 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 (118 bhp) in 2006 to 107 kW (146 bhp) 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 (54 bhp)
to 66 kW (90 bhp), in other words by 65 percent.
Even more impressive 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.
Le Mans event
Meanwhile, on June 22/23, Audi will be competing at the
classic 24-hour race at Le Mans for the 15th time. For Audi, the challenge is particularly great,
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.
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