Mechanism Study About The Ingested Gas In The Orifice At The End Of Injection

In recent years, it can be found from a series of experimental studies that during the needle closing process, the gas will ingested into the orifice. In this paper, the visualization of the fuel flow characteristics inside the nozzle has been research, the controllable high-speed flash shadow imaging was used to photography the nozzle area, and used the STAR- CCM + to calculate the numerical simulation of the flow in the orifice at the end of injection.Build a controllable high-speed flash shadow imaging test bench, the basic principle is to use the different scattering rate when light go through the liquid and gas,so we can get the images in liquid and gas regions with different gray-scale. under different conditions, the images of different injection time show: the bubble inside the orifice and sac are due to the ingested gas outside of the nozzle;When the nozzle size is not the same, the volume of the cavitation inside the nozzle will influence the bubble size in the nozzle and sac.In order to analyze the mechanism of the gas ingesting into the orifice at the end of injection, this paper uses the VOF model to capture the gas-liquid interface change, adds the cavitation model and turbulence model at the same time, establishes the two-dimensional calculation model for the flow field inside the nozzle to simulate the cavitation and ingested gas in the orifice at the end of injection, and conduct the numerical simulation under the different initial fluid jet velocity, injection time and orifice length. The result shows that under the different initial fluid jet velocity, injection time and orifice length, with the increase of speed variation rate and orifice length, the maximum cavitation volume inside the orifice and the increase of ingested gas volume linearly increase in two stages with the decreasing growth rate in the later stage. Within a scope of speed variation rate and orifice length, the maximum cavitation volume is equal to the ingested gas volume, and the latter will be slightly larger than the former beyond the scope. Therefore, the cavitation volume inside the orifice is the main factor affecting the ingested gas volume. The non-dimensional cavitation number C is put forward,find the change rule between the cavitation number and the maximum cavitation volume and ingested gas volume. Finally, simulate the other two models with the different orifice diameter, and the simulation result is used to verify the correctness of the conclusion.Therefore, under different initial conditions, we can use the cavitation number C to analyze the change rule between the cavitation volume and ingested gas volume inside the orifice.