LIF Visualization of Liquid Fuel in the Cylinder of a Spark Ignition Engine

Abstract

Laser-induced fluorescence (LIF) has been used to investigate the presence and location of liquid fuel films on the combustion chamber walls of a port fuel-injected engine. A frequency-tripled, Nd: YAG laser provided full-field illumination of the combustion chamber through a window in the piston crown. LIF from liquid-phase gasoline was imaged onto a gated, intensified solid-state camera, and recorded in real-time, synchronous with the engine, on video tape. The technique has been demonstrated on a production, four-valve head, comparing open and closed-valve injection timing. A cold start was simulated by motoring the engine at constant speed before enabling injection and ignition. For open-valve injection, liquid fuel was observed on and around the exhaust valves during the first injected cycle, and combustion occurred by the fourth cycle. For closed-valve injection, a detectable fuel film was seen near the intake valve seat by the fifth cycle, and combustion began by the eighth cycle.