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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.

A mathematical model was used in order to investigate the trajectories of evaporating fuel droplets in the port of a four-valve per cylinder gasoline engine equipped with sequential port-injection. The effects on the trajectories and evaporation of the droplets of several parameters were investigated, including: injection timing, droplet initial size, droplet initial injection velocity, air temperature, fuel temperature, engine speed and load, fuel properties (in particular, volatility). The results of the computer simulation show that the most influential parameters on the droplet evaporation and trajectories are: the initial droplet momentum (droplet size and injection velocity), injection timing, air temperature, engine speed and fuel volatility.