喷油嘴内流特性与喷雾特性研究及结构优化

Research and Optimization on Flow and Spray Characteristics of Nozzles

结合柴油机喷油嘴内部流动和喷雾数值计算模型,基于支持向量机构建了喷油嘴性能代理模型,研究了喷油嘴结构参数对内部流动和空化现象及喷雾特性的影响,并通过多目标遗传算法NSGA—Ⅱ对喷油嘴结构进行了多目标优化。结果表明:喷孔直径从0.10 mm增大到0.20 mm,喷孔出口质量流量增大336.31%,孔内产生剧烈空化现象,喷雾贯穿距和索特平均直径(Sauter mean diameter,SMD)分别增大74.04%和46.19%。减小喷孔长度会改善喷雾性能,但同时使孔内空化现象加剧,影响流动性能。入口圆角半径的存在能有效减弱孔内的空化现象,提高雾化性能,当入口圆角半径从0增大到0.016 mm时,出口质量流量和喷雾贯穿距分别增大22.50%、17.76%,SMD减小12.22%。喷孔倾斜角越小,空化现象越弱,其对喷雾特性影响较小。优化后的喷油嘴出口质量流量和喷雾贯穿距分别增大了21.19%和11.91%,燃油蒸气体积和SMD分别减小了81.38%和1.37%,流动性能和喷雾性能均得到改善。

The numerical model coupled the diesel injection nozzle flow and the spray was established.A surrogate model of the nozzle performance was established based on the support vector machine(SVM).The effect of the nozzle structural parameters on the internal flow and cavitation characteristics and the spray characteristics were studied,and the multi-objective optimization of the nozzle structure was carried out based on genetic algorithm NSGA—Ⅱ. Results show that when the orifice diameter increases from 0. 10 mm to 0. 20 mm,the nozzle outlet mass flow rate increases by 336. 31%. Severe cavitation occurs in the orifice.The spray penetration and the Sauter mean diameter(SMD) increase by 74. 04% and 46. 19%,respectively.Reducing the orifice length will improve the spray characteristics,but at the same time,it will aggravate the cavitation phenomenon in the orifice and affect the flow characteristics. The existence of the round radius of the entrance can effectively weaken the cavitation phenomenon in the orifice and improve the atomization performance. When the round radius of the entrance increases from 0 to 0. 016 mm,the mass flow rate and the spray penetration increase by 22. 50% and 17. 76%,respectively,and the SMD decreases by 12. 22%. The smaller the orifice slant angle, the weaker the cavitation phenomenon. And it has little effect on spray characteristics. After optimization,the nozzle outlet mass flow rate and the spray penetration increase by 21. 19% and 11. 91% respectively, while the fuel vapor volume and the SMD decrease by 81. 38% and 1. 37%,respectively. Both the flow performance and the spray performance are improved.