We talked about FSI. But what does it stand for? The name FSI denotes Audi’s petrol direct injection technology where, in contrast to the conventional system of injecting fuel into the intake manifold, the fuel is injected directly into the combustion chambers. The superior thermodynamics of this method enhance the engine’s overall efficiency.
FSI engines develop more power and dynamism than conventional units with indirect manifold injection – and they do so whilst achieving a very high standard of fuel economy at the same time. By boosting efficiency in this way, Audi has once again demonstrated the brand’s proverbial "Vorsprung durch Technik".
In June 2001, Audi’s direct petrol injection technology confirmed its tremendous potential in what must be the most challenging endurance test in the world when an FSI power unit propelled the Audi R8 prototype sports car to an impressive overall victory in the Le Mans 24 Hours. This success was followed by numerous further victories over the next four years.
The FSI engines from Audi combine petrol direct injection with a newly developed, demand-controlled single-piston high-pressure pump for each bank of cylinders. This pump feeds exactly the right quantity of fuel into the system to attain the operating pressure of between 30 and 100 bar in the common rail. In the intake tract, which includes the two-stage variable intake manifold, charge motion flaps swirl the air intake to produce a fast, tumbling motion.
In this way a homogeneous fuel-air mixture with a lambda ratio of one is formed in the combustion chambers. Injecting the fuel directly also has the effect of cooling the chambers, thereby reducing the tendency to knock. This gave the development team sufficient scope to raise the basic compression ratio to 12.5:1 in both V engines, compared to a ratio of around 10.5:1 for indirect-injection engines.
The result is a more efficient combustion process resulting in higher power delivery, that translates first and foremost into more spontaneous response. The FSI units demonstrate another of their fortes in the frequently used partial throttle range where they burn less fuel than an indirect-injection engine.
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