Let's Hear It for Gasoline Direct Injection
has absolutely dominated Le Mans and other endurance-racing venues, and the company gives a lot of credit to a single technical concept: Gasoline Direct Injection. As the name suggests, a GDI system injects its gasoline directly into the combustion chamber, not into intake ports, a throttle body or some such.
For road-going applications, GDI's extremely precise control of injection allows two distinct strategies of operation, stratified charge for light load and a homogenous mixture for power on demand. There are resulting benefits in efficiency, emissions and fuel economy (see "Technology Update: The Last Internal-Combustion Engine?" December 1997).
GDI cars have been on the streets for a while now, introduced by , which did a lot of R&D in the area. So far, these cars are Japan- and Europe-only, where low-sulfur gasoline is available. California's Phase 2 Reformulated Gasoline more than suffices for GDI's special catalytic needs, but our federal-standard gasoline doesn't cut it. Audi is introducing GDI on the 1.6-liter A2 FSI, its tidy city car that, alas, doesn't make it to the U.S. Its 4-cylinder powerplant has a 12.1:1 compression ratio and a common-rail injection operating at pressures as high as 1600 psi. The NOx generated by its lean-burn regime is handled in part by a barium-coated catalyst functioning in "storage" mode.
GDI Wins Races Roday
Audi has certainly demonstrated GDI benefits in endurance racing. As an interesting tidbit, there's no need for the concept's light-load regime, as more than 70 percent of a Le Mans lap is spent at full throttle. Nonetheless, Audi notes that other efficiencies of GDI translate into two fewer pitstops at a race like Le Mans.
Competitors at GM rate GDI even higher. They reckon it could give an advantage of 4 to 7 laps over a 24-hour race. In fact, the company cited its own lack of GDI as one reason for ending the LMP program. GM's European arm, Opel, offers several cars with GDI powerplants, their technology licensed from Mitsubishi. But it's a long way from R¨sselsheim to the Circuit de la Sarthe.
GDI Won Races Years Ago
Back in the 1950s, the fabled 300SLR sports racers and W196 Grand Prix cars had GDI, essentially derived from aircraft practice. The concept had supplanted carburetion in aircraft as more amenable to negative-g maneuvers. (It was to avoid fuel starvation in carbureted aircraft that the "wingover" initiated a dive with inverted flight.)
Mercedes fitted direct injection in its race cars for enhanced distribution of fuel to their inline-6s, inherently long powerplants. Another nuance of these engines was their crankshaft, its drive taken off the middle rather than the rear; this, to minimize torsional loads.
GDI in Tomorrow's Formula 1?
You can bet that Formula 1 engineers are thinking hard on the GDI concept. However, F1 revs exceeding 19,000 rpm make for a real challenge. Quoted in Race Tech, a specialized British monthly, Audi Sport's Ulrich Baretzky observed that it takes roughly 5 microseconds to get the fuel injected and mixed at 6000 rpm. Thus, there'd be less than 2 microsec. to perform this at F1 revs.
When this is achieved (and you'll note I don't say "if"), it'll be comparable to the introduction of pneumatic valve return.