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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