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A production six-hole conical sac-type nozzle incorporating a quartz window in one of the injection holes has been used in order to visualize the flow under cavitating flow conditions. Simultaneous variation of both the injection and the back chamber pressures allowed images to be obtained at various cavitation and Reynolds numbers for two different fixed needle lifts corresponding to the first- and the second-stage lift of two-stage injectors. The flow visualization system was based on a fast and high resolution CCD camera equipped with high magnification lenses which allowed details of the various flow regimes formed inside the injection hole to be identified. From the obtained images both hole cavitation initiated at the top inlet corner of the hole as well as string cavitation formed inside the sac volume and entering into the hole from the bottom corner, were identified to occur at different cavitation and Reynolds numbers.

The application of computational methods for the development of a high performance four-stroke motorcycle engine has here been evaluated. A single dimension fluid dynamic code has been employed to simulate engine performance at full load, and data predicted from computer simulation have been compared with experimental results. After the abovementioned validation process, computer simulation techniques were applied to develop a variable geometry exhaust system so as to optimize volumetric efficiency over a wider speed range. These techniques proved to be powerful and effective in the identification of the modifications required to obtain the engine performance targets.