Simulation analysis of flow characteristics of Jatropha curcas oil in diesel injector

The formation and development process of fuel spray has a great influence on fuel atomization, fuel evaporation, fuel-air mixing, and combustion, which can further influence the properties of a diesel engine. The atomization process and its quality are affected not only by the mutual friction between the fuel spray and ambient air, but also by the flow behavior in the nozzle orifice such as the cavitation effect and the turbulent flow among which the flow disturbance induced by the cavitation is the first important factor effecting the atomization of fuel spray. A lot of research studies on an alternative fuel, Jatropha curcas oil (JCO), for diesel fuel have been carried out by both domestic and international scholars with the focus mainly on the preparation methods, and physical and chemical properties as well as the performance and the pollutant emissions of a diesel engine fueled with JCO. Nevertheless, the issues related to a systematic study of the cavitation flow and the spray outflow characteristics, which have a great influence on the injection and atomization of JCO, are seldom reported. In the present paper, a three-dimensional gas-liquid two-phase model of cavitation flow was developed, which took the influence of injection conditions on fuel viscosity, fuel density, and bubble number density into consideration. After the validity of the model was verified, a three-dimensional numerical simulation that was about the influences of injection pressure, injection back pressure and fuel temperature on the cavitation flow of JCO in a diesel nozzle was carried out. The results showed that: the mean flow velocity at outlet (MFVO) and the mass flow rate is enhanced gradually with the increment of injection pressure, and the discharge coefficient decreases simultaneously. However, the cavitation effect does not change significantly. The injection backpressure has little influence on the flow characteristics of JCO in the diesel nozzle. MFVO, mass flow rate, and discharge coefficient raise remarkably with the increment of JCO temperature, and at the same time, the cavitation effect is significantly enhanced. The cavitation effect and MFVO of JCO are lower than those of diesel fuel under the same injection condition, but whether the mass flow rate and the discharge coefficient of JCO are higher than those of diesel fuel also depends on the fuel temperature. The results obtained indicate that the increment of JCO temperature will remarkably enhance the cavitation effect, strengthen the flow disturbance, and improve MFVO and the cycle fuel injection quantity, which are beneficial for the fuel injection, atomization, and the performance of a diesel engine. The research can provide references for in-depth analysis on the working process of diesel engine fueled with JCO.