Well 411A, I believe that Ozgrade3 was asking about direct (into the cylinder) fuel injection, NOT the FI used by TCM and Lyc which inject the fuel into the intake port.
The current systems provide a continuous spray of fuel into the intake port which is sucked/pushed (normally aspirated vs. turbo or super charged) into the cylinder when the intake valve is opened. On the other hand, direct injection employs a timed injector that sprays the fuel directly into the cylinder - usually on the compression stroke when both the intake and exhaust valves are closed.
The direct injection system is more complex, requiring precise timing (and duration) of the fuel spray "pulse". Since in these systems the fuel pressure is constant, the mixture is controlled by the duration of the fuel pulse. Automobile engines that use direct/timed injection use an oxygen sensor in the exhaust as part of the feedback loop to set the correct mixture.
Would such a system provide benefits for GA piston engines? Probably. Is the cost of getting FAA certification for such a system a barrier? Definately.
