| 杜慧勇,任思铭,李可,等.基于计算流体力学的柴油机选择性催化还原系统尿素水溶液喷雾特性分析[J].内燃机工程,2023,44(6):20-27. |
| 基于计算流体力学的柴油机选择性催化还原系统尿素水溶液喷雾特性分析 |
| Spray Characteristic Analysis of Urea Water Solution in A Diesel Selective Catalytic Reduction System Based on Computational Fluid Dynamics |
| DOI：10.13949/j.cnki.nrjgc.2023.06.003 |
| 关键词:柴油机 选择性催化还原 尿素水溶液 喷雾 仿真 |
| Key Words:diesel engine selective catalytic reduction（SCR） urea water solution（UWS） spray simulation |
| 基金项目:国家重点研发计划项目（2016YFD0700700） |
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| 摘要:为探究影响柴油机排气管尿素水溶液（urea water solution， UWS）雾化效果的因素，搭建了UWS喷射试验台架，通过激光粒度仪测得尿素液滴粒径分布，并运用Rosin-Rammler 函数对试验获得的累积粒径分布进行非线性拟合，利用计算流体力学（computational fluid dynamics， CFD）软件对柴油机负荷工况、UWS喷射温度和排气管壁温3种不同因素对UWS喷雾雾化特征、NH3浓度分布及液膜形成的影响进行仿真计算。结果表明：低负荷工况下的排气流量和温度低，UWS喷入量少，尿素液滴分解NH3的速率较低，80 ms时刻NH3主要分布在排气管中游；中高负荷工况，排气温度高、UWS喷入量多，有利于尿素蒸发热解生成NH3，该时刻NH3浓度区域偏离轴线，贴近排气管上表面；喷雾液滴粒径随UWS喷射温度的升高而减小，范围在1~12 μm，空间内NH3浓度小幅增加，液膜沉积率随喷射温度升高显著降低；排气管壁温对UWS喷雾液滴粒径和蒸发热解速率影响较大，壁温升高加快了液滴粒径减小的速度，当壁面温度为473 K时，150 ms时刻下液滴粒径主要集中在30 μm以下，附着壁面的液膜厚度明显减小直至消失，尿素结晶问题得以改善。 |
| Abstract:In order to investigate the factors affecting the atomisation of urea water solution （UWS） in diesel exhausts， a UWS injection test rig was set up and the particle size distribution of urea droplets was measured by laser particle size measurement. A Rosin-Rammler function was used to fit the cumulative particle size distribution to the test. The computational fluid dynamics （CFD） software was used to simulate the effects of three factors， namely the exhaust flow rate， exhaust temperature and urea injection volume， on the atomisation characteristics， NH3 concentration distribution and liquid film formation of the UWS spray. The results show that under low load conditions with low exhaust flow and temperature and UWS injection quality， the rate of NH3 decomposition was low， and NH3 concentration region was distributed in the middle of exhaust pipe at 80 ms. Under medium and high load conditions， high exhaust temperature and large UWS injection quality were conducive to NH3 generation by the evaporation and pyrolysis of urea. At that time， NH3 concentration region deviated from the axis and was close to the upper surface of exhaust pipe. The particle size of UWS spray droplets near the upper side of the inner wall of the exhaust pipe was small， mainly concentrated in the range of 7~30 μm. The particle size of droplets near the center line of the spray was distributed in the range of 50~110 μm. The particle size of droplets near the downstream nozzle was large， mainly concentrated in the range of 110~130 μm. UWS injection temperature has little effect on spray particle size distribution. To some extent， the increase of UWS temperature was conducive to the decrease of spray particle size， ranging from 1 to 12 μm， and the increase of NH3 concentration. The deposition rate of liquid film decreased with increasing UWS temperature and injection time. Wall temperature of the exhaust pipe had a greater impact on droplet size and evaporative pyrolysis rate of UWS spray. Whereby an increase in wall temperature accelerated the decrease of droplet size， resulting in smaller droplets and more uniform atomization. The thickness of the liquid film decreased as the wall temperature increases. When the wall temperature is 473 K， droplet sizes were primarily concentrated below 30 μm at 150 ms. The thickness of the liquid film adhering to the wall was significantly reduced until it disappeared， thereby improving urea crystallization. |
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