柴油机SCR系统尿素水溶液的喷雾特性
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摘要
通过建立柴油机SCR后处理系统的UWS喷射雾化模型,综合考虑UWS液滴在排气管道中的湍流扰动、变形、破碎、碰撞聚合和碰壁反弹等一系列理化过程,研究UWS的喷雾雾化分解特性,分析了喷嘴喷射压力、喷孔喷射角度α、喷雾锥角β、喷嘴偏置角度θ和排气管径长比对UWS液滴分解的影响.结果表明:喷射压力过小时,UWS液滴将呈液柱或大液滴状,喷射雾化效果差,NH_3平均体积分数随喷射压力的增大呈线性增大;α对UWS分解有显著影响,随着α的增加,NH_3平均体积分数升高;β对NH_3均匀性系数影响显著,随着β的增大,排气管内壁面附近NH_3的分布更加均匀;随着θ的增大,NH_3平均体积分数不断增大,但其均匀性系数急剧下降;NH_3平均体积分数随排气管直径的增大而减小,后逐渐趋于平缓.
Establishing the urea water solution(UWS) spray atomization model for selective catalytic reduction(SCR) aftertreatment system in diesel engine, the physical processes of UWS droplets of turbulence disturbance, distortion, breakup, collision-merging and wall-impingement bounce in exhaust pipe were investigated comprehensively. The effects of nozzle injection pressure, nozzle injection angle of α, spray cone angle of β, nozzle offset angle of θ and diameter-to-length ratio of exhaust pipe on the decomposition of UWS droplets were analyzed. The results show that when the injection pressure is too small, the UWS spray tends to be liquid column or large droplets with poor spray atomization ability of UWS, and the NH_3 average volume fraction is increased linearly with the increasing of injection pressure. The value of α has significant effect on UWS decomposition, and the NH_3 average volume fraction is increased with the increasing of α. The value of β has significant effect on NH_3 uniformity coefficient, and the distribution of NH_3 tends to be uniform with the increasing of β.With the increasing of θ, the average volume fraction of NH_3 is increased, while the uniformity coefficient is decreased sharply. With the increasing of exhaust pipe diameter, the average volume fraction of NH_3 is first decreased with latter gradually gentle decreasing.
Establishing the urea water solution(UWS) spray atomization model for selective catalytic reduction(SCR) aftertreatment system in diesel engine, the physical processes of UWS droplets of turbulence disturbance, distortion, breakup, collision-merging and wall-impingement bounce in exhaust pipe were investigated comprehensively. The effects of nozzle injection pressure, nozzle injection angle of α, spray cone angle of β, nozzle offset angle of θ and diameter-to-length ratio of exhaust pipe on the decomposition of UWS droplets were analyzed. The results show that when the injection pressure is too small, the UWS spray tends to be liquid column or large droplets with poor spray atomization ability of UWS, and the NH_3 average volume fraction is increased linearly with the increasing of injection pressure. The value of α has significant effect on UWS decomposition, and the NH_3 average volume fraction is increased with the increasing of α. The value of β has significant effect on NH_3 uniformity coefficient, and the distribution of NH_3 tends to be uniform with the increasing of β.With the increasing of θ, the average volume fraction of NH_3 is increased, while the uniformity coefficient is decreased sharply. With the increasing of exhaust pipe diameter, the average volume fraction of NH_3 is first decreased with latter gradually gentle decreasing.
引文
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[12] 王静,王谦,徐航,等.车用柴油机SCR系统NOx转化效率影响因素[J].内燃机学报,2015,33(5):453-460.WANG J, WANG Q, XU H, et al. Influential factors on NOx conversion efficiency of vehicle SCR system[J]. Transactions of CSICE, 2015, 33(5): 453-460.(in Chinese)
[2] 帅石金,唐韬,赵彦光,等.柴油车排放法规及后处理技术的现状与展望[J].汽车安全与节能学报,2012,3(3):200-217.SHUAI S J, TANG T, ZHAO Y G, et al. State of the art and outlook of diesel emission regulation and aftertreatment technologies[J]. Journal of Automotive Safety and Energy, 2012, 3(3): 200-217.(in Chinese)
[3] CHOI C, SUNG Y, CHOI G M, et al. Numerical analysis of NOx reduction for compact design in marine urea-SCR system[J]. International Journal of Naval Architecture & Ocean Engineering, 2015, 7(6):1020-1034.
[4] 王谦,张铎,王静,等.车用柴油机Urea-SCR系统数值分析与参数优化[J].内燃机学报,2013,31(4):343-348.WANG Q, ZHANG D, WANG J, et al. Numerical analysis and parametric optimization on Urea-SCR system of vehicle diesel[J]. Transactions of CSICE, 2013, 31(4): 343-348.(in Chinese)
[5] BALETA J, VUJANOVI, et al. Numerical modeling of urea water based selective catalytic reduction for mitigation of NOx from transport sector[J]. Journal of Cleaner Production, 2015, 88(12):280-288.
[6] GAN X B, YAO D W, WU F, et al. Modeling and si-mulation of urea-water-solution droplet evaporation and thermolysis processes for SCR systems[J]. Chinese Journal of Chemical Engineering, 2016, 24(8):1065-1073.
[7] HELDEN V R, VERBEEK R, WILLEMS F, et al. Optimization of urea SCR deNOx systems for HD diesel engines[C]//SAE Technical Paper Series. USA: SAE Publication Group, Paper Number:2004-01-0154.
[8] 唐韬,赵彦光,华伦,等.柴油机SCR系统尿素水溶液喷雾分解的试验研究[J].内燃机工程,2015,36(1):1-5.TANG T, ZHAO Y G, HUA L, et al. Experimental study of urea solution spray and decomposition of SCR system for diesel engine[J].Chinese Internal Combustion Engine Engineering,2015,36(1):1-5.(in Chinese)
[9] STR?M H, LUNDSTR?M A, ANDERSSON B. Choice of urea-spray models in CFD simulations of urea-SCR systems[J]. Chemical Engineering Journal, 2009, 150:69-82.
[10] CAPETILLO A, IBARRA F. Multiphase injector modelling for automotive SCR system:a full factorial design of experiment and optimization[J].Computers and Mathematics with Applications, 2017, 74:188-200.
[11] ZUKERMANA R, VRADMANA L, HERSKOWITZA M, et al. Modeling and simulation of a smart catalytic converter combining NOx storage ammonia production and SCR[J].Chemical Engineering Journal, 2009,155:419-426.
[12] 王静,王谦,徐航,等.车用柴油机SCR系统NOx转化效率影响因素[J].内燃机学报,2015,33(5):453-460.WANG J, WANG Q, XU H, et al. Influential factors on NOx conversion efficiency of vehicle SCR system[J]. Transactions of CSICE, 2015, 33(5): 453-460.(in Chinese)