Numerical Simulation And Experimental Validation Of Internal Nozzle Flow Characteristic Of Injector Under Hot Fuel Conditions

Because of the complexities of the nozzle flow, such as the cavitation phenomena and turbulence, the mechanism of the flow dynamics and its effect on the subsequent spray is unclear. The existing researches mainly focus on the influence of nozzle structure and injection pressure on the characteristics of internal flow. However, there is few research about the internal flow affected by the fuel temperature. Most experiments were conducted at room temperature.The shell temperature can be up to523K under ordinary conditions. The properties of fuel (like viscosity, density, vapor pressure and surface tension) change as the temperature changes, thus has different effects on the internal flow characteristics. Therefore, it is very necessary to do further study of effect of temperature on the internal flow characteristics.The development of researches for the internal flow characteristics was analyzed. A test bench based on an enlarged transparent nozzle was established to get necessary data. According to the mass, energy, momentum conservation laws, Rayleigh equation and so on, the mathematical model of internal flow was set up. The mass flow, velocity at the outlet, cavitation distribution and non-dimensional flow coefficients under different temperature and pressure conditions were considered in the analysis. The CFD results of the internal flow characteristics in the2D nozzle were compared with the experiments. Moreover, the flow characteristics of diesel in3D nozzle were also simulated to study the effect of temperature and back pressure on internal flow.The result showes that:the CFD results agree well with the experiments; critical super cavitation conditions are achieved easier when fuel temperature rises, injection pressure rises or back pressure drops; the mass flow rate first rises then decreases with the rise of temperature; while the volume flow rate and effective vefocity increases shows positive correlation to temperature and injection presure; Reynolds number rises with the temperature rising, the cavitation number decreases exponentially with increases in the Reynolds numbers; besides, discharge coefficient increases with the development of cavitation flow, then shows a slight decrease after supercavitation.