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燃油喷雾是直喷式发动机燃烧的关键过程,喷雾模拟的精度决定了燃烧计算的可靠性.然而,在KIVA和商业CFD代码中,传统喷雾模拟技术对网格精度非常敏感.因而,预测的发动机性能和排放依赖于计算网格.导致这个问题的两个主要原因是液滴碰撞算法和气液相间耦合.为了提高喷雾模拟精度,采用交错网格液滴碰撞(CMC)算法和气相速度插值算法对原始KIVA代码进行了修正.在定容燃烧室和直喷式柴油机条件下,分别从喷雾结构、预测平均液滴尺寸和喷雾贯穿距三个方面检验了改进KIVA代码对喷雾模拟精度的改善.结果表明,网格依赖性显著降低.通过这些改进,喷雾结构的失真现象消失.在定容燃烧室计算中,预测的平均液滴尺寸的不确定性从30μm减小到5μm;在发动机模拟中,这种不确定性进一步减小到2μm.在中等和精细网格条件下,发动机模拟预测的喷雾贯穿距也获得了较好的一致性.
Fuel Spraying is a key process for direct injection engine combustion and the accuracy of the spray simulation determines the reliability of the combustion calculation.However, traditional spray simulation techniques are very sensitive to the grid accuracy in KIVA and commercial CFD codes.Thus, the predicted engine Performance and emissions depend on the computational grid.The two main causes of this problem are the droplet collision algorithm and the gas-liquid phase coupling.In order to improve the accuracy of the spray simulation, staggered grid droplet collision (CMC) algorithm and gas velocity interpolation algorithm The original KIVA code was modified.The improvement of the accuracy of the spray simulation was verified by the improved KIVA code under the conditions of constant volume combustion chamber and direct injection diesel engine, respectively from the spray structure, the predicted average droplet size and the spray penetration. The results show that the grid dependency is significantly reduced, and the distortion of the spray structure disappears with these improvements.In the calculation of the volumetric combustion chamber, the predicted average droplet size uncertainty decreases from 30μm to 5μm; in the engine simulation , This uncertainty is further reduced to 2 μm. Under medium and fine grid conditions, the engine simulation predicts that the spray penetration is also better Consistency.