综合可视化试验和数值模拟手段,研究分析了柴油机颗粒捕集器(DPF)主动再生时柴油氧化催化器(DOC)上游柴油喷雾特性及柴油在DOC内的氧化过程.利用高速摄影装置拍摄了柴油喷雾图像,分析了喷雾贯穿距和喷雾锥角,并利用相位多普勒粒子分析仪(PDPA)对喷雾粒径进行了测量.标定了DOC内的柴油氧化模型和喷雾模型,在此基础上对柴油喷雾及燃油在DOC内的氧化过程进行了模拟.试验结果表明:柴油喷射速率越高,喷雾贯穿距和喷雾锥角越大;喷射速率对喷嘴出口处喷雾粒径分布有较大影响,沿喷雾轴线方向液滴的索特平均直径(SMD)随大粒径液滴数的变化而变化.模拟结果表明:柴油喷雾特性决定了排气管路和DOC入口处的碳氢(HC)分布;DOC出口处温度分布与DOC入口处HC分布具有密切的对应关系;碰壁及重力作用使得HC向排气管路底部集中,HC质量浓度接近2%;管路底部柴油过浓使得DOC出口截面底部的对应区域温度较低,低于450℃;增加排气管路长度可促进喷雾与气体的混合均匀性,缓解管路底部的柴油过度集中现象.%The diesel spray characteristics at the upstream of a diesel oxidation catalyst (DOC) during active regeneration of a diesel particulate filter (DPF) and the diesel oxidation process in the DOC were investigated by means of integrated visualization experiment and numerical simulation.To the end, high-speed photography device was used to capture diesel spray images, and the spray droplet sizes were measured with a phase Doppler particle analyzer (PDPA).Based on the calibration of the diesel spray model and the DOC model, the diesel spray and oxidation process were simulated.Experimental results indicate that the higher the fuel injection rate, the greater the spray cone angle and penetration distance.The injection rate has a greater effect on spray droplet size distribution at the nozzle outlet.The SMD along the axial direction of spray varies with the number of large droplets.Simulation results show that the hydrocarbon distributions in the exhaust pipe and DOC inlet are determined by the diesel spray characteristics.The temperature distribution at DOC outlet has a close correlation with the hydrocarbon distribution at DOC inlet.The spray impingement and gravity force will cause hydrocarbon to accumulate at the bottom of exhaust pipe so that the mass concentration of hydrocarbon is close to 2%.While too much diesel fuel at the bottom of the pipeline will lead to lower temperature of the corresponding area at the bottom of the outlet section of the DOC, which is lower than 450℃.Increasing the length of exhaust pipeline can promote the mixing uniformity of the spray and gas, and alleviate the phenomenon of excessive concentration of diesel fuel at the bottom of the pipeline.
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