In Cylinder High Speed and Stroboscopic Video Observation of Spray Development in a DI Diesel Engine

For high-speed imaging a newly developed eight-fold CCD camera, which permits framing rates of up to one million pictures per second, was used to obtain pictures of the injected sprays during the operation of a diesel engine. For the particular case studied here the framing rate was set at 50,000 pictures per second. This rate was sufficient to resolve the temporal development of the sprays in the transparent version of the four-cylinder, in-line, 1.9 litre DI production diesel engine of Volkswagen. The advantage of the camera is that it needs no light pulses for illumination, but can operate with a continuous light source. Each of the CCD chips is arranged around a central eight face reflecting pyramid, which splits the light coming from the camera lens to each CCD chip. The chips can be shuttered freely (asynchronously) at programmable inter-frame spacings thus permitting operation with continuous illumination. In this particular case a 30 Watt halogen lamp was used. Also stroboscopic pictures of the sprays were taken with one CCD camera at different delay times after the beginning of injection showing the cycle to cycle variations of the spray structure. As an example of the results obtained with these techniques, a comparison between the sprays resulting from two-spring and one-spring injectors was made, showing that in the first stage of lift of the two-spring injector the sprays are more disperse but at the same time more stochastic in shape compared to those of a one-spring injector.