A Comparison of Fuel Distribution and Combustion During Engine Cold Start for Direct and Port Fuel Injection Systems

Experiments have been conducted in a firing single-cylinder spark-ignition engine employing a Ford Zetec cylinder head that has been modified to operate with either standard port-fuel-injection, air-forced port-fuel-injection or direct-injection. The engine utilizes a fused silica cylinder and therefore provides extensive optical access to the combustion chamber. Tests were conducted using a constant speed simulated cold start procedure, which is composed of an initial start-up transient and a quasi-steady-state idle period. In this procedure, the engine is briefly motored at 889 rpm and then combustion commences shortly after the start of fuel injection. Measurements which were performed include in-cylinder pressure as well as intake valve, exhaust valve, piston, cylinder, head, and intake air temperature throughout each cycle of the test period. The engine-out total hydrocarbon emissions were also measured. Engine start quality is quantified by the length of the initial start-up period and the stability of the quasi-steady-state idle. Based on these two parameters, the influence of three fuel injection systems, operating temperature, ignition timing, and injection timing on the engine performance during cold start are presented and discussed. In addition, the pre-combustion fuel distribution is measured using two-dimensional laser-induced fluorescence. The pre-combustion fuel distribution images of the three injection systems at different crank angles and times during the test are presented and discussed relative to engine performance.