LIF and Flame-Emission Imaging of Liquid Fuel Films and Pool Fires in an SI Engine During a Simulated Cold Start

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 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 expected that fuel films on the head near the exhaust valves are a direct source of unburned hydrocarbon emissions, that fuel films on the cylinder wall are a source of fuel blowby into the crankcase, and that pool fires are a source of soot.