Investigation of cavitation in real size diesel injection nozzles

Abstract

Abstract The laser light sheet and shadowgraph techniques have been applied to investigate cavitation phenomena in the spray hole of real size diesel injection nozzles and the breakup at the spray hole exit. The experiments were performed with a Bosch Common Rail system for generating unsteady injection conditions. Rail pressures up to 60 MPa were used. The diesel-like test oil was injected into a chamber which could be pressurized up to 1.5 MPa. The local position and range of cavitation films, lying between the flow and the nozzle wall, as well as single cavitation bubbles could be observed at different times of the injection process. The pictures of the light sheet experiment taken with a CCD camera were compared with photographs taken by the shadowgraph technique under the same injection conditions. As a result the cavitation films could be observed as thin objects which do not extend into the internal flow of the injection nozzle. In addition, even under higher injection pressures, no accumulation or foam of bubbles could be noticed in the spray hole. This leads to the conclusion that there is an intact liquid core leaving the nozzle even at high injection pressures. Further experiments dealt with the coherence of flow conditions at the start of injection and the spray patterns produced at the beginning of the injection process. These measurements were made with a special optical setup including a high-speed ICCD camera.