Simulation Research on Influence of Secondary Injection Strategy on Particulate Emission of GDI Engine
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摘要: 为降低GDI发动机微粒排放，搭建了某型缸内直喷汽油机的三维数值模型并利用AVL-Fire对发动机微粒生成过程进行仿真模拟，探究缸内微粒的生成机理和两次喷油策略对微粒生成的影响规律。首先对原机喷油参数下的单次喷射策略进行了仿真研究，其次，在单次喷射的基础上进行了燃油两次喷射，探究喷油时刻及喷油比例对微粒生成的影响规律，得到了如下的研究结论：原机喷射策略下未完全蒸发的油膜遇到火焰时在油膜表面产生扩散燃烧导致微粒大量生成；二次喷射策略下，随第二次喷油时刻推迟，最终微粒质量分数和数量浓度均先减小后增加，优化后的二次喷油策略最终微粒质量分数为1.28×10-11，最终微粒数量浓度为2.99×1013，较单次喷射策略分别降低了46.89%和31.42%。因此，合理的制定二次喷油策略可以减少微粒的产生。Abstract: In order to reduce the particulate emissions of GDI engines, a 3D numerical model of a certain type of cylinder direct injection gasoline engine was built and the AVL-Fire was used to simulate the generation process of engine particulates. The particulate generation mechanisms in cylinders and secondary injection strategies for particulates were investigated. The effect of the law is firstly simulated by the single injection strategy under the original fuel injection parameters. Secondly, two injections of fuel were performed based on the single injection to explore the influence of injection timing and the injection ratio on particle generation. According to the influence laws, the following conclusions have been obtained:in the original jet injection strategy, the incomplete evaporation of the oil film on the surface of the oil film caused diffusion combustion and resulted in the generation of large amounts of soot; Under the secondary injection strategy, as the second injection timing postponed, the final soot mass fraction and the number concentration firstly decreased and then increased. The optimized secondary fuel injection strategy has a final soot mass fraction of 1.28×10-11, and the final soot number concentration was 2.99×1013, which were 46.89% and 31.42% lower than the single injection strategy respectively. Therefore, a reasonable development of secondary injection strategy can reduce the production of soot.
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Key words:
- GDI engine /
- secondary injection /
- soot /
- CFD simulation
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表 1 某型号GDI汽油机基本参数
参数 设计值 压缩比 10.5:1 排量 1 395 cm3 冲程/缸径 80 mm/74.5 mm 额定功率 100 kW(5 500 r/min) 最大扭矩 250 N·m(2 250~3 500 r/min) 增压形式 废气涡轮增压 
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表 2 边界条件设置
壁面类型 边界壁面名称 温度设定值/K 固定 Inlet(进气岐管入口) 318.15 固定 Intake port(进气岐管壁面) 350 固定 Chamber(气缸盖壁面) 500 固定 Liner(气缸侧壁面) 461 移动 Piston(活塞顶部) 533
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表 3 初始条件设置
参数名称 设置值 缸内压力/Pa 123 952 缸内温度/K 921.75 湍动能/(m2·s-2) 2 湍流长度尺度/m 0.00 384 进气压力/Pa 137 725 进气温度/K 333.15
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表 4 两次喷射策略仿真方案
序号 喷油比例 第一次喷油时刻 第二次喷油时刻 Case1 5:5 425 ℃A 480 ℃A Case2 5:5 425 ℃A 500 ℃A Case3 5:5 425 ℃A 530 ℃A Case4 5:5 425 ℃A 560 ℃A Case5 5:5 425 ℃A 580 ℃A Case6 3:7 425 ℃A 最优第二次喷油时刻 Case7 4:6 425 ℃A 最优第二次喷油时刻 Case8 6:4 425 ℃A 最优第二次喷油时刻 Case9 7:3 425 ℃A 最优第二次喷油时刻
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