Combining Port Fuel Injection With Direct Injection

Direct InjectionWith all the auto manufacturers working to reach new fuel economy standards set by the U.S. for future vehicles, we are seeing new technologies, materials and techniques.

One of the newer technologies is direct fuel injection. Direct fuel injection has actually been around for decades, but it was only recently that materials development and computer speeds have reached the point where it would not only work, but work within the strict emissions regulations that are in place.

So what is direct injection? Right now there are two types of injection systems common on gasoline-powered vehicles — port injection and direct injection.

Both systems use computer-controlled electric injectors to spray fuel into the engine, but the difference is where they spray the fuel. Port injection sprays the fuel into the intake ports where it mixes with the incoming air.

The injectors are often mounted in the intake manifold runners and the fuel sits in the runners till the intake valve opens and the mixture is pulled into the engine cylinder.

Direct injection has the injectors mounted in the cylinder head and the injectors spray fuel directly into the engine cylinder, where it then mixes with the air. Only air passes through the intake manifold runners and past the intake valves with direct injection.

At Sterling Performance, we are developing the capability of combining port fuel injection with direct injection. With port fuel injection, you’re looking at low speed, idle emissions and drivability; direct injection will be for high speed running. In this case, we’re developing two systems on a single engine, interchanging between port fuel injection and direct injection to get better missions and performance out of the engines.

Source:; Jim Kerr; October 20, 2011.

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