Fuel and Flame Imaging in SI Engines

An optical imaging technique has been developed which allows the visual observation of fuel vapour within selected planes in optically accessed combustion chambers of Spark Ignition engines. The technique utilises fluorescence radiation of hydrocarbon molecules to image fuel vapour distribution. This fluorescence radiation is induced by a pulsed laser light sheet projected into the transparent combustion chamber and it can be observed with an intensified camera gated synchronously with the pulsed laser at any selected time instant of the engine cycle. In addition to recording mixture distribution, the camera arrangement also allows visualisation of the gasoline flame propagation. These imaging methods are used for the investigation of mixture formation and flame development in a transparent, disc-shaped combustion chamber under low speed and low load conditions. The effect of fuel injection timing on mixture distribution is analysed in detail and operating conditions are demonstrated which may either yield homogeneous or inhomogeneous mixture at the time of ignition. Together with flame photography, the visualisation of mixture distribution before and during combustion presents a feasible tool for the analysis and tuning of fuel injection and in-cylinder mixture formation.