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May 2006: The diesel comes of age |
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By Bill Vance
The diesel engine made a significant
breakthrough this March when an
Audi R10 diesel powered sports
racer beat the worlds best gasoline powered
cars to win the prestigious Sebring,
Florida 12-hour race. It was like a coming
out party for diesel, just as the Mazda victory
in the 1991 Le Mans, France 24-hour
race had been for the Wankel rotary
engine.
With thousands of hours of dynamometer
and track testing
behind it, this was the
competition debut for
Audiís low-slung 925
kg diesel racer. A bigger
test will come in June
when it competes at Le
Mans. Audi is no stranger there; its gasoline
R8 racers have won five times in the
last seven years. It stepped aside in 2003 to
allow Volkswagen-owned Bentley to win
(using largely Audi technology).
Diesel cars are highly regarded in
Europe, driven by motor fuel prices far
higher than they are in North America.
More than half the new cars sold there,
including Audis, are diesels, whereas in
North America they have always been a
niche product. They enjoyed a brief popularity
spike during the energy panic of the
late 1970s and early 1980s, but that subsided
when oil crises memories faded.
Audi, a division of Volkswagen, hopes
racing publicity will contribute to changing
the dieselís image. Long an advocate of
diesels, Volkswagen/Audi wants the R10 to
publicize the significant advancements it
has made in diesel technology.
Diesel cars have been around since
1936 when Mercedes-Benz introduced its
260D diesel passenger car. Intended for
taxi use where high annual kilometres
would offset the higher initial cost, M-B
was surprised to discover regular motorists
buying them for their ruggedness and
economy.
But the compression
ignition oil burner had
several strikes against it
for passenger cars.
Although undoubtedly
more economical,
thanks to the reduced pumping losses of
unthrottled induction (power is regulated
by fuel flow, not air flow) and a compression
ratio typically twice that of a gasoline
engine, it developed a reputation for being
smelly, smoky, noisy and slow. But its 30 %
better fuel economy and bullet proof durability
made it the power of choice for longhaul
trucks and other transportation and
industrial applications.
Such advances in diesel technology as
quick-start glow plugs, direct fuel injection,
common rail fuel systems and particulate
filters have made them faster, quieter, cleaner
and more powerful. While limited
in overall crankshaft speed due to the combustion
process, diesels develop very strong
torque in the 1500 to 3500 rpm range
where motorists do most of their driving.
The Audi R10 racer is a showcase for
VW/Audiís latest diesel technology. It has a
twin turbocharged, double overhead cam,
4- valve-per-cylinder, 5.5 litre, 90-degree
aluminum V12. The air-to- water intercooled
turbochargers pump air into the
engine at up to 27 psi, and the TDI (turbo
direct injection) fuel system is the same type
fitted to VW and Audi passenger diesels.
Fuel is fed through multi-orifice injectors
directly into the combustion chambers at a
breathtaking 29,000 psi and particulate
traps will eliminate the characteristic black
sooty smoke from the R10ís exhaust.
Peak horsepower is 650, while peak
torque is a prodigious 811 lb ft, which
required Audi to beef up gears and shafts
over the R8, and use a ceramic and carbon
fibre clutch. Peak power and torque occur
in the 3000 to 5000 rpm range, about half
that of a gasoline engine, enabling Audi to
reduce its transmission ratios from the six
used in its all conquering R8 gasoline racer,
to five in the R10. Superior fuel economy
should also reduce pit stops.
The Audi is not the first high level diesel
racer. Cummins Diesel, based in Indiana,
entered diesels in the Indianapolis 500 in
1931, í34, í50 and í52. In 1952 it was on
the pole, and ran as high as fifth before
retiring with an obstructed turbo intake.
Whether Audi wins Le Mans 2006
remains to be seen, but it will no doubt give
a good account of itself. If it doesnít win
this year, it seems like only a matter of time
before a diesel racer captures the worldís
most prestigious endurance race.
You can also go to billvanceautohistory.ca
for author books.
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