高压燃油喷射诱导激波对喷雾特性的影响

Effect of Shock Waves Induced by High-Pressure Injection on Spray Characteristics

为了研究诱导激波对喷雾特性的影响,采用纹影法和仿真模拟的方法对不同喷射压力、不同环境介质条件下的喷雾和激波特性进行研究.结果表明:在相同喷射压力和环境密度下,在燃油喷射初期,存在激波条件下的喷雾贯穿距小于无激波条件下喷雾贯穿距,从仿真结果来看,在燃油喷射初期激波为附体激波,激波后环境气体密度和压力均大于激波前,激波后具有更大密度和压力的环境气体会阻碍喷雾的发展,从而导致贯穿距变小.在燃油喷射中后期激波与喷雾分离之后,存在激波条件的喷雾贯穿距则要高于无激波条件下的喷雾贯穿距.激波还可以增强燃油与空气混合程度,对增大喷雾体积有一定的促进作用,且促进效果会随着激波强度的增大而更加明显,有利于油、气混合气的形成.超高压喷射仿真结果表明,当喷射压力达到240 MPa和320 MPa时,喷射初期斜激波的末端会产生弓形激波,可以加剧湍流运动促进油、气混合,此外激波的产生使激波处环境气体温度升高,当喷射压力达到320 MPa时,激波处温度最多可升高16%,这有利于燃油的雾化蒸发.

Shock waves could disturb the surrounding gas.Then the turbulent gas will affect the spray.In this paper,image photography and numerical simulation were used to investigate the effect of shock waves on spray characteristics.The experimental results show that the spray penetration with attached shock waves is shorter than that without shock waves under the same injection pressure and ambient density conditions during the initial injection stage.From simulation results,the shock waves attach the spray tip during the initial stage.The density and pressure of the gas behind the shock waves are higher than that in the front of the shock waves.And the ambient gas with high density behind the shock waves will hinder the spray development.After the shock waves are separated from the spray,however,the spray penetration with shock waves is longer than that without the shock waves.The shock wave can also promote the mixing degree of the fuel and the ambient gas and increase the spray volume.The effect will be more obvious with the increase of the intensity of shock waves,benefit for the mixture formation.The simulation results for the spray under super-high injection pressure condition show that the bow shock wave is generated at the tail of oblique shock wave under the injection pressure of 240MPa and 320 MPa.Furthermore,the shock waves can increase the gas temperature up to 16%at the injection pressure of 320 MPa,improving the atomization and evaporation of spray.