Cranking-Startup Intake Port and In-Cylinder Mixture Preparation Behavior in a CFR Gasoline Engine

Engine startup experiments with intake port sampling were performed in a modified fuel injected single cylinder gasoline CFR research engine. Immediately after fuel injection, port fuel-air vapor sampling was performed in order to quantify the role of the fuel injector in creating a combustible mixture for the first cycle of engine startup. In-cylinder sampling was also performed to clarify the role of other mixture preparation mechanisms in the startup process. Sample analysis was performed using gas chromatography. Experimental data were also collected during steady-state operating conditions at the same intake port pressure and temperature as that of the first cranking cycle for comparison. Results show that approximately ½ to ¾ of a near stoichiometric combustible 1st cycle charge, as a function of first cycle fueling, is produced immediately after enriched cranking fuel injection. In contrast, the fuel injection event provides only ¼ of the required fuel-air vapor mixture under similar steady-state engine operation. Finally, detailed chromatograph results show the dominant role of the lighter ends of the gasoline in the post fuel injection intake port vapor for both cranking and steady-state engine operation.