Gasoline Direct Injection (GDI) Engine is a kind of spark ignition engine where gasoline is directly injected into the combustion chamber. This is quite different from the conventional spark ignition engines where a mixture of fuel and air is inducted into the combustion chamber. The major advantages of a GDI engine are increased fuel efficiency and high power output. This is achieved by the precise control over injection of fuel. The fuel timings are varied according to the load conditions. In conventional spark ignition engines, fuel and air are mixed in the carburetor, which is outside the cylinder. This leads to wastage of fuel between the carburetor and the cylinder. There is also a problem of injection timing because of the lag between pressing of the accelerator and entry of fuel into the cylinder. In GDI, as gasoline is directly injected into the cylinder, the problem of fuel wastage during mixing is solved. The fuel in GDI is injected with precise timing which leads to complete combustion of the fuel. The idea to inject gasoline directly into combustion chamber was researched earlier either to increase power or to lower fuel combustion. The GDI engines attain both the objectives by operating in two modes of combustion: Ultra Lean Combustion Mode and Superior Output Mode.
Ultra Lean Combustion Mode
In the Ultra Lean combustion mode the air fuel ratio is much lower than that in the conventional spark ignition engines. The engine operates in this mode under normal conditions, when not much acceleration is required. In this mode the fuel is injected into the combustion chamber during the latter stages of the compression stroke. This results in an optimally stratified air fuel mixture just below the spark plug. Thus this mode enables the combustion of relatively lean air fuel mixture.
Superior Output Combustion Mode
The GDI engine switches automatically to the Superior Output Combustion Mode when the car accelerates. The fuel is injected during the intake stroke and it forms a homogeneous mixture.
