FLUORESCENCE IMAGING INSIDE AN INTERNAL-COMBUSTION ENGINE USING TUNABLE EXCIMER LASERS

Tunable excimer lasers are used to obtain 2-D images of molecular (and some state-specific) density distributions inside a cylinder of a modified four-cylinder in-line engine that has optical access. Naturalfluorescence (i.e., without a laser) is used for some OH pictures, normal laser-induced fluorescence (LIF) forthose of NO and of the isooctane fuel, and laser-induced predissociative fluorescence (LIPF) for other OHpictures and for those of 02. Relevant spectroscopy is done to find the laser and fluorescence frequenciesneeded to measure isolated species. LIPF works well at high pressures, is state specific, and is ideally suitedto follow turbulent processes. No similar measurements in engines have been previously reported. Picturesare taken in succeeding engine cycles. Their sequence is either at a particular point of the engine’s cycle toshow cyclic fluctuations, or at succeeding portions of the cycle to illustrate the progress of the gasdynamics orof the combustion. © 1990 Optical Society of America.