Numerical Simulation Study of Spray Wall Impingement Combustion
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摘要: 燃油喷雾碰壁是小型高压直喷式柴油机中普遍存在的现象. 燃油碰壁会影响缸内燃烧过程，进而显著地影响柴油机的动力学、经济性和排放性. 为了更好地认识燃油喷雾碰壁燃烧现象，该研究采用数值模拟的方法对该过程进行计算，探究其特殊的燃烧特性. 研究结果表明：在碰壁喷雾的两阶段燃烧过程中，喷雾碰壁促进喷雾径向发展半径和卷吸高度的增加，促进近壁面油气混合，在近壁面形成有利于低温点火的条件. 低温燃烧反应在混合气较为稀薄的近壁面区域开始，随后向碰壁喷雾中心浓混合气区域发展. 随着低温氧化燃烧持续放热，碰壁喷雾雾束中心区域温度逐渐升高，同时积累大量甲醛. 由于喷雾碰壁会导致碰壁雾束中心形成较浓混合气，并且低温燃烧放热量较少，导致部分碳氧化物无法完全燃烧，增加了碳烟的生成量. 另外随着高温燃烧的进行，温度持续升高，碰壁喷雾卷吸更多环境气体，进而产生大量氮氧化物.Abstract: Fuel spray wall impingement is a common phenomenon in small high-pressure direct injection diesel engines. Fuel spray wall impingement influences the in-cylinder combustion process, and significantly impacts the engine's dynamics, fuel economy, and emissions. To better understand the combustion characteristics of fuel spray wall impingement, the numerical simulation was applied to calculate the process and explore this process. The results show that, during the 2-stage combustion process of spray wall impingement, the impingement promotes the radial development radius and the vortex height of the spray, enhances oil-gas mixing near the wall, and forms favorable conditions for low-temperature ignition near the wall. Low-temperature combustion reactions start in the near-wall region, where the mixture is relatively dilute, and then develop into the dense mixed gas area in the center of the impinging spray. As low-temperature oxidation combustion continues to release heat, the maximum temperature in the center of the impinging spray will gradually increase, and a large amount of CH2O will accumulate. Meanwhile, the impinging spray can cause the formation of a more concentrated mixture in the center of the impinging spray, and low-temperature combustion would release less heat, resulting in the incomplete combustion of some carbon, and increasing the amount of soot generated. Additionally, as high-temperature combustion proceeds, the temperature will continue rising, and the impinging spray will draw more oxygen, generating a large amount of NOx through oxidation reactions.
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Key words:
- spray wall impingement /
- spray combustion /
- soot /
- NOx
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图 1 在Kuhnke薄膜飞溅模型中，4种壁面相互作用类型
Figure 1. Four types of wall interaction in the Kuhnke thin-film splash model
图 2 碰壁喷雾液滴空间分布与实验对比
Figure 2. Comparison between the spatial distributions of impinging spray droplets and experimental results
图 3 喷雾贯穿距与实验对比
注 为了解释图中的颜色，读者可以参考本文的电子网页版本，后同.
Figure 3. Comparison between the spray penetration distances and experimental results
图 6 CH2O、OH和温度分布云图(白色轮廓线为当量混合分数Zst=0.068)
Figure 6. Distribution maps of CH2O, OH, and the temperature (the white contour line represents equivalent mixture fraction Zst=0.068)
图 7 低温燃烧阶段CH2O空间分布云图
Figure 7. Spatial distribution maps of CH2O during the low-temperature combustion stage
图 8 高温燃烧阶段OH空间分布云图
Figure 8. Spatial distribution maps of OH during the high-temperature combustion stage
图 9 不同时刻混合质量分数-温度散点图
Figure 9. Scatter plots of the mixture mass fraction and the temperature at different moments
表 1 喷雾碰壁等实验参数
Table 1. Experimental parameters of spray wall impingement et al
parameter value injection pressure Pi/MPa 15 ambient pressure Pa/MPa 0.1 ambient temperature Ta/K 296 wall temperature Tw/K 473 impingement distance l/mm 22.5 
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表 2 实验参数
Table 2. Numerical simulation parameters
parameter value injection pressure Pi/MPa 40 impingement distance l/mm 40 ambient temperature Ta/K 813 wall temperature Tw/K 408
下载: 导出CSV
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