Comparison of Single and Dual Spray Fuel Injectors During Cold Start of a PFI Spark Ignition Engine Using Visualization of Liquid Fuel Films and Pool Fires

Video imaging has been used to investigate the evolution of liquid fuel films on combustion chamber walls during a simulated cold start of a port fuel-injected engine. The experiments were performed in a single-cylinder research engine with a production, four-valve head and a window in the piston crown. Flood-illuminated laser-induced fluorescence was used to observe the fuel films directly, and color video recording of visible emission from pool fires due to burning fuel films was used as an indirect measure of film location.

The imaging techniques were applied to a comparative study of single and dual spray fuel injectors for both open and closed valve injection, for coolant temperatures of 20, 40 and 60°C. In general, for all cases it is shown that fuel films form in the vicinity of the intake valve seats. For closed valve injection, films also form below the intake valves and below the squish region between the intake valves and the cylinder wall, while for open valve injection additional fuel films form below the exhaust valves. It is proposed that fuel films on the head near the exhaust valves are a possible source of unburned hydrocarbon emissions, that pool fires are the main source of soot emissions from properly-maintained gasoline vehicles, and that soot-laden fuel films on the cylinder wall are the main source of soot contamination of the crankcase oil.