For spark ignition engines, the most effective way to reduce the overall fuel consumption and CO2 emissions respectively is the implementation of gasoline direct injection technology. In comparison to the current wall and air guided systems, the direct injection system of the second generation - the spray guided DI- is the most promising one with respect to fuel economy and emission. In order to exploit its full potential, a thorough combustion process development regarding injector and spark plug design and their positioning within the combustion chamber is essential. Especially multihole injectors offer many degrees of freedom with regard to the nozzle shape and spray pattern. To reduce the development work and costs necessary to identify the ideal nozzle characteristic and spray pattern, reliable CFD models are necessary.
Although many investigations of the in-nozzle flow of real size multihole injectors for diesel applications have been carried out within the last decade, publications of research work using optical gasoline injectors, especially multihole injectors, are very limited. In order to improve and validate the CFD models, a comprehensive understanding of the flow characteristic within gasoline injectors is essential.
This paper presents the results of an investigation of the in-nozzle flow characteristic of a Valve Covered Orifice (VCO) type nozzle. A transparent real size single hole injector was developed and adapted to a pressure chamber. A series of experiments for the visualisation of the onset and development of cavitation inside the nozzle and the initial fuel break up process was conducted applying the back light illumination method. The influence of different chamber and injection pressures, as well as different nozzle shapes on the injection process and cavitation development were examined.