Wednesday, 19 November 2014

GM’s Direct Injection Explained(SATURN)


GM’s Direct Injection Explained




Gasoline direct injection differs from the fuel delivery process of a conventional engine by delivering fuel directly into the combustion chamber, where it is mixed with air drawn into the chamber. The combustion process of conventional fuel-injected engines uses air and fuel that are mixed in the intake port or intake manifold prior to being introduced into the combustion chamber.
Direct injection is a continuation of the evolutionary process of moving the fuel introduction point closer to the combustion location to improve control.
With the Ecotec 2.0L Turbo, fuel is introduced directly to the combustion chamber during the intake stroke. As the piston approaches top-dead center, the spark plug ignites the mixture, giving the name spark ignition direct injection (SIDI). The fuel injectors are located beneath the intake ports. SIDI allows the mixture to be “leaner” — less fuel, more air — at full power.


SIDI also permits a slightly higher compression ratio than if the fuel were delivered with conventional fuel injection. The result is better fuel consumption at part and full throttle. The engine uses conventional spark plugs similar to those in other Ecotec engines.
A high-pressure, returnless fuel system is employed. It features a high-strength stainless steel fuel line that feeds a variable-pressure fuel rail. Direct injection requires higher fuel pressure than conventional fuel-injected engines, and an engine-driven high-pressure fuel pump is used to supply up to 2,250 psi of pressure. The system regulates lower fuel pressure at idle — approximately 752 psi and higher pressure at wide-open throttle. The cam-driven high-pressure pumps works in conjunction with a conventional fuel tank-mounted supply pump.
Direct injection’s precise fuel delivery enables more complete combustion to help reduce emissions, particularly on cold starts — the time when most engine emissions are typically created. Also, direct injection permits a higher compression ratio in the engine, which positively influences fuel economy. At certain power levels, the boosted SIDI engine can provide significant fuel economy benefits compared to a larger displacement naturally aspirated engine.
 

 

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