Numerical study on the effect of air-assisted nozzle shape on kerosene spray and flow characteristics

Abstract

Due to its physical characteristics of large viscosity and non-volatilization, aviation kerosene has a poor atomization effect in aeroengine cylinder, and is inappropriate for aviation piston engine unless high pressure injection is used. Air-assisted injection can effectively solve this problem. In the paper, the CFD software is used to establish a 3-D numerical model of the air-assisted injector, and the influence of the nozzle shape on the airflow movement and interaction between gas and liquid is investigated. The accuracy of the simulation model is confirmed by the comparison of the simulation results with the spray morphology and penetration of the spray experiments in the constant volume bomb. Based on this, three nozzle shape models are established to simulate the air-assisted spray flow field of aviation kerosene RP-3 under various ambient back pressures. The influence of nozzle shape on the flow state of compressed air and spray characteristics is compared and analyzed. The results show that when the back pressure is 0.09 MPa, the oblique shock waves can be observed near both large and small circular arc nozzle exits, and the attenuation degree of airflow velocity by the oblique shock wave is relatively small. The stronger interaction between the gas-liquid two phases is beneficial to fuel atomization. Moreover, the normal shock wave appears in the conical nozzle where the injected nitrogen has less kinetic energy. Several large-scale vortices are generated in the near field of the spray, which promotes the mixing of fuel and surrounding nitrogen. Therefore, for aviation kerosene which is difficult to atomize, a large and small circular arc shaped nozzle with strong atomizing ability should be used. When the mixture is required to be evenly distributed in the combustion chamber, the conical nozzle should be preferred.