Study On Cavitation And Gas Ingestion In Diesel Nozzle After The End Of Injection

In this paper,the cavitation and gas ingestion of diesel engine nozzle are studied by means of experiment and simulation.In the experiment,a visualized test-bed based on high-speed camera was built,and the effects of injection pressure,injection amount and nozzle length on the cavitation and gas ingestion inside the nozzle were studied.In the simulation,the effects of the needle valve's setting speed and maximum lifting height on the cavitation and gas ingestion in the nozzle are studied.In addition,a real six-hole nozzle model was established,and cavitation and gas ingestion in each nozzle were studied.Firstly,the test bench was improved to test the nozzle with different orifice lengths.It was found that the nozzle with long orifice was shorter than that with short orifice,and cavitation and gas ingestion occurred earlier and more in the oil breaking stage.The cavitation in the jet orifice increases with the increase of jet pressure,but the cavitation in the pressure chamber has an opposite trend.The backflow gas in the nozzle decreases with the increase of injection pressure,and the shape is dispersive.With the increase of the injection amount,the cavitation amount and gas ingestion amount in the injection hole show a decreasing trend.In addition,a certain amount of experimental research has been carried out on the linear cavitation in the injection nozzles.Subsequently,it is concluded that the low pressure caused by cavitation failure in the nozzle is the main cause of air gas ingestion.In the calculation,the influence of the needle valve's setting speed and maximum lift height on cavitation and gas ingestion is studied emphatically,which is mainly reflected in that the cavitation and gas ingestion amount in the pressure chamber increase with the increase of the needle valve's setting speed and decrease with the increase of the maximum lift height of the needle valve.However,the influence of the two on cavitation in the nozzle orifice is small.Finally,the actual six-hole nozzle is calculated,and it is found that the maximum cavitation amount and gas ingestion amount in each nozzle basically increase with the increase of nozzle Angle.When the gas ingestion is stable,due to the mutual influence of each nozzle,the gas ingestion amount does not change obviously with the nozzle Angle after stabilization.