Race cars are hardly green machines, but Audi's purpose here is to persuade a sceptical US public that diesel technology is not just for trucks and tractors any more. The R10 is clearly a very capable prime mover, beating the entire gasoline competition at the very first test. Note that the crankcase is made from aluminium rather than cast iron, despite the high torque demand - the compression ignition parameters of gasoil limit diesel race engines to 5000-6000 RPM.

I don't know much about Sebring but at Le Mans the present rules restrict only tank volume. However, diesel contains 10-12% more energy per gallon than gasoline does. In an endurance race, that translates to fewer refuelling stops and hence, a competitive advantage. If Audi wins Le Mans as well, I would not be surprised to see a change in the rules next year.

Btw, in this case, the particulate filters are a bit of a marketing ploy. The most criticial test of a PM filter is igniting and burning off layers of accumulated soot without thermal damage to the monolith. This never occurs during a race because at full power, soot is burnt off long before it starts clogging the filter.

Is the pressure figure right? 1,600-bar is 24,000 psi. Most hydraulic systems (which I'm familiar with) run about 3,000 psi. Compressed Natural Gas is typically stored at 3,600 psi. I'm wondering if the fuel-system pressure figure has got an extra zero on it. Alternately, I could understand 1,600 psi for a fuel system (kinda high, but believable).

Tony

I only need 1/10 of that power and torque but this can give a message to those power loving people that diesel is one of their choice.

(a) Tony, Mike -

current-generation common-rail diesel injection systems do indeed operate at up to 1600 bar in series production vehicles, which can mean as high as 2000 at the injector tip because designers take advantage of wave dynamics in the conduits. VW had for the longest time insisted on individual pump-injectors for each cylinder, because that permits pressures as high as 2400 bar and avoids heating up the fuel. Higher pressures produce smaller droplets and improved admixture of the fuel and air. The combustion is more rapid and complete.

However, separating the pump from the injector has several advantages:
- piezoelectric actuation permits multiple pre- and post-injections even at high RPM, reducing combustion noise and emissions
- common-rail injectors are a little smaller, which is important in designing the cylinder head
- greater economies of scale, as everyone but VW is using common rail in new vehicles today. The company has announced it will switch to common rail in the foreseeable future.

The cental high-pressure pump is controlled to produce only the pressure level that is required for a given engine load. At first glance, it might seem that Audi's 1600 bar system is conservative - this is not true, as peak pressures are only rarely required in regular passenger cars but all the time in endurance racing.

(b) JB -

the fuel economy gap between diesels and gasoline engines narrows substantially as you approach full power. Your argument absolutely holds true for regular passenger cars that are operated at low load most of the time, but far less so for race conditions.

As for ethanol, perhaps that was an exception.

Note that the history of endurance racing in general, and Le Mans in particular, is one of constant cycling of rules to address both parity in competition and political/commercial interests. The ACO made a conscious effort to provide an advantage to diesel cars in its most recent rules revisions, including a 1500cc displacement advantage for turbocharged cars, larger inlet restrictors, and higher boost pressure.

More power plus better specific fuel consumption is critical at Le Mans, which is a high-speed circuit with over 8.4 miles between pit stop opportunities. Rules that enable a team to skip two pit stops in 24 hours, for example, provide a decisive tactical advantage.

While I agree that the rules will probably stay stable through 2007 to allow Peugeot some success when it enters next year, an adjustment to restore parity with gasoline-engined cars is likely in 2008 (perhaps a displacement increase for the SI cars or a smaller restrictor for CIs).

None of this should detract from Audi's magnificent technical achievement however. Very few new prototypes, diesel or not, win Sebring on the first try, and Audi and the Joest team are to be commended.

Audi is very slow to bring its great cars across the pond. The A3 is new in the USA--why not one of their amazing diesel quattros? You cant get them if you want them.

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Part of the reasons for quiteness of the Audi, is the engine is probably Revving up only up to 5000 RPM, whereas the gas engines will be buzzing aroud 8-12K. The slower engine speed means less air is moving through the engine and exhaust system. Diesels burn cooler so the thermal expansion of gas in the engine is less than gas engines. Also the fact they have installed particulate filters and cats on the exhaust system, will silence some of the exhaust noise. The Gas engines are most likely running straight pipes, you could actually take most diesel engines and run straight exhaust and barely notice the difference. Mainly due to the speed of the exahust gases, much slower (cooler) than gasoline.

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