04-10-2010, 02:47 PM
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Gasoline direct injection
INTRODUCTION
In recent years, legislative and market requirements have driven the need to reduce fuel consumption while meeting increasingly stringent exhaust emissions. This trend has dictated increasing complexity in automotive engines and new approaches to engine design. A key research objective for the automotive engineering community has been the potential combination of gasoline-engine specific power with diesel-like engine efficiency in a cost-competitive, production-feasible power train. One promising engine development route for achieving these goals is the potential application of lean burn direct injection (DI) for gasoline engines. In carburetors the fuel is sucked due to the pressure difference caused by the incoming air. This will affect the functioning of the carburetor when density changes in air are appreciable. There was a brief period of electronically controlled carburetor, but it was abandoned due to its complex nature. On the other hand in fuel injection the fuel is injected into the air. The objective can be attained by using gasoline direct injection technology in the automobiles.
In internal combustion engines, gasoline direct injection is a variant of fuel injection employed in modern four- stroke petrol engines. The petrol/gasoline is highly pressurized, and injected via a common rail fuel line directly into the combustion chamber of each cylinder. This helps in preventing leakage loss, that occurs in the conventional carburetor when the fuel is being transferred from fuel tank to the engine cylinder.
GASOLINE DIRECT INJECTION (GDI)
In conventional engines, fuel and air are mixed outside the cylinder. This ensures waste between the mixing point and the cylinder, as well as imperfect injection timing. Gasoline direct injection engine generates the air fuel mixture in the combustion chamber. During the induction stroke only the combustion air flows through the open intake valve. The fuel is then directly injected into the combustion chamber by the fuel injector. But in the GDI engine, petrol is injected directly into the cylinder with precise timing, eliminating waste and inefficiency.