ABSTRACT
The continuing development of gasoline direct-injection engines is under consideration in the automotive industry in Europe and Japan, due to disatisfaction with the first-generation engines and due to increasing competition from direct injection diesels. The advantages of adopting the direct-inj ection gasoline concept, because of its outstanding potential for fuel economy and CO2 reduction, have been well documented [ 1 -4] and remain its strongest selling point. Different configurations of combustion chambers have been designed, corresponding to wallo, air-or spray-guided systems, each with advantages and disadvantages [5] . The configuration adopted in this study is the spray-guided system, using the close spacing approach where the basic aim is to provide consistenly a slightly rich mixture around the spark plug at the time of ignition, by allowing enough time for vaporization of the fuel after injection and preventing wall wetting, In order to realize the maximum possible fuel economy, the engine has to be operated unthrottled. Burning an overall lean mixture in spark ignition engines but with local charge stratification [6], offers a number of advantages but the difficulties remain in achieving a stratified charge over the full regime of low loads and speeds; some degree of throttling may thus be required, resulting in losses under some operating conditions. Planar Laser Induced Fluorescence (PLIF) is a well established technique for in-cylinder measurements of local fuel concentration and fuel distribution, and it has been widely used for investigations in both port injection and direct injection gasoline engines [7-1 1 ] .
