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A novel experimental technique was used to investigate the in-cylinder air-fuel ratio excursions of a port-injected spark-ignition engine during load and fuel transients. This involved sampling directly from the engine cylinder using a fast flame ionisation detector (FID) system throughout an engine transient test. All tests were conducted with the coolant at the normal operating temperature of 90°C. The research engine used was a 1.6ltr four-cylinder multi-point fuel injection spark-ignition (SI) engine with four-valves-per-cylinder, with sequential injection and an electronic management system. The engine transient involved a rapid throttle opening within about 15msec. Various load steps were investigated at 2000rev/min along with the effect of altering the type of fuel injector.

A mathematical model has been developed which describes the evaporation and trajectories of fuel droplets during their flight in the inlet manifold of port-injected gasoline engines. Based on the model, a computer simulation program was developed, and sample results of this program are given in this paper. Extensive results obtained using the simulation program are described in a companion paper. The simulation program can be used as a tool to improve understanding of mixture preparation in port injected engines. Such effects as: engine load and speed, air and fuel temperature, fuel type, fuel injection velocity, injection timing, and spray droplet size can be investigated.