How Direct Injection Works

Saturn's 2009 Outlook, Sky Red Line, and upcoming Vue 2-Mode hybrid models all feature powerplants using "direct injection" (DI) technology to improve power, efficiency, and emissions. In a conventionally port fuel injected engine, air and fuel are mixed before they enter the combustion chamber. With General Motors' DI engines, fuel is sprayed directly into the cylinder where it is mixed with air. As the piston approaches top-dead center, the mixture is ignited by the spark plug; and when the fuel vaporizes in the cylinder, the air and fuel mixture is cooled. This enables the use of a higher compression ratio in the combustion chamber, which improves the engine’s power and efficiency.

The video animation below demonstrates how DI works.

On cold starts, direct injection can be controlled to create a richer air/fuel mixture around the spark plug, making it easier to ignite in a cold engine. This results in a smoother operation of the engine and lower emissions during the cold start and warm-up, when most harmful tailpipe emissions are typically created. GM's direct injected engines reduce cold-start vehicle emissions by 25%.

Because the fuel is injected directly into the combustion chamber, direct injection uses higher fuel pressure than conventional fuel injected engines. This is enabled by a special high pressure pump driven by one of the engine’s camshafts.

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