FSI stands for gasoline direct injection, a technology in which fuel is injected directly into the combustion chambers, rather than into the intake manifold in the traditional manner. More favorable in terms of thermodynamics, this method improves the efficiency of the engine. FSI engines achieve higher performance and better dynamics than conventional engines, with better efficiency. Whether they have four, five, six, eight, ten or twelve cylinders, all gasoline engines from Audi today employ the FSI principle.
Another common trait of all Audi engines is the homogeneous fuel-air mixture. In a so called stoichiometric ratio, one kilogram (2207 lb) of gasoline mixes with 14.7 kilograms (32.41 lb) of air – equivalent to a volume of approximately 12400 liters (437.90 cubic ft), since air is extremely light.
A turbocharger makes a TFSI (Turbo fuel stratified injection) out of an FSI. In 2004 Audi was the first manufacturer worldwide to combine forced induction with gasoline direct injection. The two technologies harmonize perfectly: the directly injected fuel swirls intensely in the combustion chamber, which in turn cools the walls of the combustion chamber. This solves an old problem with turbo technology – the tendency toward early spontaneous ignition of the mixture at hot spots in the combustion chamber due to strong heat build-up at high compression, a phenomenon known as knocking. With its TFSI engines, Audi can achieve high compression ratios, to the benefit of combustion quality and thermodynamic efficiency – and consequently fuel efficiency.
Like TDI engines, FSI and TFSI engines obtain fuel through a common rail injection system. In the gasoline engines, however, significantly lower injection pressures of about 150 bar (2176 psi) are sufficient, owing to the lower compression ratios of these engines versus self igniting diesel engines. The primary advantages are the same as in the TDI: the compact design of the system and the freedom it allows for controlling the injection event.
Advantages:
-Better fuel distribution and better fuel charge inside the combustion chamber
-During the injection process the fuel gets evaporated, cooling the cylinder chamber
-Higher compression ratios, which translates into more power
-Increased fuel combustion efficiency
-Higher power during pick-up of vehicle
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