Investigation of cavitation in real size diesel injection nozzles

The laser light sheet and shadowgraph techniques have been applied to inves tigate cavitation phenomena in the spray hole of real size diesel injection nozzles and the breakup at the spray hole exit. The experiments were perfo rmed with a Bosch Common Rail system for generating unsteady injection cond itions. 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 loca l position and range of cavitation films, lying between the flow and the no zzle wall, as well as single cavitation bubbles could be observed at differ ent times of the injection process. The pictures of the light sheet experim ent taken with a CCD camera were compared with photographs taken by the sha dowgraph technique under the same injection conditions. As a result the cav itation films could be observed as thin objects which do not extend into th e internal how of the injection nozzle. In addition, even under higher inje ction 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 co re 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. Thes e measurements were made with a special optical setup including a high-spee d ICCD camera. (C) 1999 Elsevier Science Inc. All rights reserved.