闪沸喷雾孔几何形状对孔内流动特性影响的数值模拟

doi:10.3969/j.issn.1674-8484.2024.03.009

摘要/Abstract

摘要：

研究了汽车直喷汽油机喷嘴的几何形状对于闪沸喷雾孔内流动以及相变过程的影响机理。基于热不平衡假设建立了一维的两相相变流动模型，对于具有不同喷孔流道长度、直径、入口处圆角以及流道锥角的结构，分析了闪沸喷雾孔内流动的特性。将该模型结果与作者团队先前的实验结果进行了精度比对，验证了模型的准确性。结果表明：喷孔流道长度越长，孔径越小，从而孔内相变越剧烈。流道入口处圆角会减少喷孔内部蒸汽的生成。收缩型喷孔压降较小，孔内蒸汽相的生成也相应减少，从而扩张型喷嘴增大蒸汽产生速率。不同的喷孔结构，改变了流道内的压力以及速度分布；压力分布影响了气泡的生长速率，速度分布影响了气泡的生长时间，而两者共同作用影响了孔内的相变特性。

关键词: 汽车动力, 直喷汽油机, 闪沸喷雾, 热不平衡, 孔内流动, 两相流, 数值模拟

Abstract:

This paper investigated the influence of nozzle geometry on the in-nozzle flow and phase-change process of flash boiling sprays in the direct-injection gasoline-engine cars. A one-dimensional two-phase-flow model was developed based on the thermal non-equilibrium assumption to analyze the in-nozzle flow characteristics of the flash boing spray with different nozzle lengths, different diameters, different rounding angles at the inlet, and different taper angles. The model’s results were verified through the accuracy comparison with the previous experimental results by the authors' team. The results show that the longer the nozzle channel length, the smaller orifice diameter, and the more intense of the phase transition in nozzles, while the round corners at the nozzle entrance reduces the vapor generated inside nozzles. The convergent nozzle has a smaller pressure drop and the generation of vapor phase inside the nozzle is reduced accordingly, while the divergent nozzle increases the vapor generation rate. The different nozzle geometries change the pressure distribution and the velocity distribution in the nozzle. The pressure distribution governs the bubble growth rate, while the velocity distribution affects the bubble growth time, both of which ultimately affect the phase change characteristics within the nozzle.

Key words: automotive power, gasoline direct-injection engines, flash boiling spray, thermal non-equilibrium, in-nozzle flow, two-phase flow, numerical simulations

中图分类号:

U464.136+.1

尹鹏, 许敏. 闪沸喷雾孔几何形状对孔内流动特性影响的数值模拟[J]. 汽车安全与节能学报, 2024, 15(3): 360-367.

YIN Peng, XU Min. Numerical simulation of the effects of nozzle geometry on the in-nozzle flow-characteristics of flash boiling sprays[J]. Journal of Automotive Safety and Energy, 2024, 15(3): 360-367.

图/表 9

参数	液相	气相
液相修正压强，p_∞ / MPa	181.96	0.00
定容比热，c_v / [kJ·(kg·K)^-1]	1.902	1.477
比热比，γ	1.368	1.074
修正比体积，b / (cm³·g^-1)	0.439	0.00
修正焓， q / (kJ·kg^-1)	-806.99	-132.82
修正熵， q' / [kJ·(kg·K)^-1]	0.00	-5.064

表1 NASG状态方程(310~430 K)正戊烷参数

图1 喷嘴流道结构示意图

喷射压力	0.5、2.0 MPa
环境压力	101、120 kPa
燃油温度	41、65、71 ℃
喷嘴长度	10、14、25 mm
流道直径	0.8、1.0、1.5、2.0 mm
喉口圆角半径	0.0、6.0 mm
锥度角	直线性、扩张型、收缩型

表2 根据文献[16]实验的仿真设计参数

图2 不同结构喷嘴内部流动的实验结果[16]

图3 不同结构的流道内部的压力、速度、气相体积分数模拟结果

图4 喷嘴喉部内的平均蒸汽体积分数。

图5 不同喉道直径流道内部的压力、速度、气相体积分数模拟结果

图6 不同流道锥角的压力、速度、气相体积分数模拟结果

图7 3种不同喷嘴的气泡初始点的比较

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