A Cooperative Fuels Research (CFR) gasoline engine has been modified to run on computer controlled Port Fuel Injection (PFI) and electronic ignition. Additionally a fast acting sampling valve (controlled by the engine control computer) has been placed in the engine’s intake system between the fuel injector and cylinder head in order to measure the fuel components that are vaporizing in the intake port immediately after the fuel injection event, and separately during the intake valve open period. This is accomplished by fast sampling a small portion of the intake port gases during a specified portion of the engine cycle which are then analyzed with a gas chromatograph. Experimental mixture preparation results as a function of inlet port temperature and pressure are presented. As the inlet port operates at higher temperatures and lower manifold pressures more of the injected fuels’ heavier components evolve into the vapor form immediately after fuel injection. The post-fuel injection fuel-air equivalence ratio in the intake port is characterized. The role of the fuel injection event is to produce from 1/4 to slightly over 1/2 of the combustible fuel-air mixture needed by the engine, as a function of port temperature. Fuel vapor sampling during the intake valve open period suggests that very little fuel is vaporizing from the intake port puddle below the fuel injector. In-cylinder fuel vapor sampling shows that significant fuel vapor generation must occur in the lower intake port and intake valve region.
