19 Apr 02
It's closely related to the Le Mans-winning R8, Audi says of its newest A2 variant, the A2 1.6 FSI. Well, they certainly don't look that similar, but the R8 and this A2 do share the same basic fuel injection technology. FSI stands for fuel stratified-charge injection, essentially a direct-injection system, as featured in the Le Mans winner and also in the original pre-production A2 concept, the Al2 study presented at the 1997 Frankfurt Motor Show, and now in Audi's first production car to feature such technology. Why fit such an advance to Audi's smallest, cheapest car rather than to, say, a range-topping A6 or A8? The A2 is, says Mischa Ehlers of Audi's Product Marketing team, "an important technology demonstrator for the Audi brand", and already showcases Audi's ASF (Aluminium Space Frame) construction, as also used for the A8, and the weight-saving benefits of an aluminium body structure. It now gets even cleverer with the addition of FSI technology.
FSI means that the A2's 1.6-litre engine can produce 13% more power, 10% more torque and 15% reduced fuel consumption than if it were a traditional indirect-injection unit. In the A2, this means an output of 110 bhp, 155 Nm (114 lb ft) of torque and 47.9 mpg. The fuel injector, which shoots fuel directly into the combustion chamber, can control injection to within thousandths of a second, at pressures of up to 110 bar. As a comparison, indirect injection operates at pressures of up to 8 bar. The higher the pressure, the better the efficiency. Audi isn't the first manufacturer to make a direct-injection petrol engine - Mitsubishi and Volvo have both offered such units for some years - but the FSI technology is particularly sophisticated.
Audi engine development engineer Rolf-Friedrich Dornhofer claims that this A2 has computer power "greater than that of the Apollo space ship", and its electronic control systems are indeed complex. The degree of control afforded in the FSI system allows, for example, for two different operating modes: homogenous and the stratified-charge mode, for which it is named. In homogenous mode, the engine operates pretty much like a traditional petrol engine, when a high power output is called for, but as it can operate at much higher injection pressures, fuel savings are still possible.
The really clever fuel-saving measures come in stratified-charge mode, however. When the engine is not under huge strain or full load, the fuel is not injected until the compression stroke, and then it passes directly into the combustion chamber. The aperture of the flap in the intake port and the special shape of the piston crown give a 'tumble motion' as the fuel passes through, meaning that the fuel is swirled through the air creating a charge, and reaches the spark plug at the moment of ignition. It's almost like a mini-thunderstorm in each cylinder. The fuel-air mixture is lean, and the excess air forms an insulating layer around each cylinder wall, reducing heat loss and again increasing operating efficiency. The engine automatically chooses the optimum operating mode, depending on the throttle position and demands.
