Mixture Preparation During Cranking in a Port-Injected 4-Valve SI Engine

This paper presents the results of an experimental investigation of the fuel-air mixing process in a port-fuel-injected, 4-valve, spark-ignited engine that was motored to simulate cold cranking and start-up conditions. An infrared fiber-optic instrumented spark plug probe was used to measure the local, crank angle resolved, fuel concentration in the vicinity of the spark gap of a single-cylinder research engine with a production head and fuel injector. The crank-angle resolved fuel concentrations were compared for various injection timings including open-intake-valve (OIV) and closed-intake-valve (CIV) injection, using federal certification gasoline. In addition, the effects of speed, intake manifold pressure, and injected fuel mass were examined. It was observed that CIV injection results in lower fuel concentrations near the spark gap during the early portion of the intake stroke relative to OIV injection, but results in essentially the same local fuel concentration at TDC of compression. This may mean either that there is significant charge stratification with OIV or that the amount of liquid fuel that remains on the port and cylinder surfaces at TDC of compression is essentially the same for the two cases. Lower intake manifold pressures were found to strongly promote fuel vaporization in the intake port and cylinder, but speed has little effect.