Impact dynamics and morphology of urea-water-solution droplets impinging on a hot plate under urea-SCR relevant conditions: Influence of surface tension

Impact dynamics and morphology of urea-water-solution droplets impinging on a hot plate under urea-SCR relevant conditions: Influence of surface tension
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DOI：
10.1016/j.fuel.2021.120671
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发表时间：
2021-08
期刊：
Fuel
影响因子：
7.4
通讯作者：
A. Kulkarni;T. Megaritis;L. Ganippa
A. Kulkarni;T. Megaritis;L. Ganippa
中科院分区：
工程技术1区
文献类型：
--
作者：
A. Kulkarni;T. Megaritis;L. Ganippa

文献摘要

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尿素选择性催化还原（SCR）系统的nox转化效率受尿素水溶液（UWS）在排气歧管中的分散程度的影响。较大尺寸的尿素液滴撞击混合分布风机和SCR系统内表面将导致沉积物的形成，这有可能降低尿素-SCR系统的有效性。在这项工作中，详细分析了UWS液滴在尿素- scr相关条件下撞击热板的液滴与壁面的相互作用。探讨了降低UWS表面张力对液滴形貌和冲击动力学的影响。加入表面活性剂DDA75后，UWS的表面张力由73.7 mN/m降至30.2 mN/m。确定了不同的液滴撞击模式，即沉积、热雾化、反弹和破裂。DDA75液滴表面张力降低59%，最大扩散因子（β max）显著提高37%。考虑壁面温度对扩散过程的影响，建立了预测UWS和DDA75液滴β max的经验关联；在不同壁温条件下，对水、碳氢化合物和替代燃料（正庚烷、正癸烷、麻疯树生物柴油和亚麻荠基替代喷气燃料）的预测β max值的平均误差小于8.2%。与UWS相比，二次DDA75液滴的粒径分布窄得多（可达36%）。表面活性剂添加的uws液滴有可能通过更好的蒸发和混合以及减少尿素沉积的形成来增强SCR系统中NO x的还原。
NO x conversion efficiency of urea-selective-catalytic reduction (SCR) systems are governed by dispersion of urea-water-solution (UWS) injected in exhaust manifold. Impingement of larger size urea droplets on mixture distribution fans as well as to the internal surfaces of SCR systems will lead to formation of deposits, which has potential to deteriorate the effectiveness of urea-SCR system. In this work, detailed analyses on droplet-wall interactions of UWS droplets impinging on a hot plate under urea-SCR-relevant conditions have been presented. The effect of lowering surface tension of UWS on droplet morphology and impact dynamics were also explored. The surface tension of UWS was lowered from 73.7 to 30.2 mN/m by adding a surfactant (DDA75). Distinct modes of droplet impact viz., deposition, thermal atomization, rebound and breakup were identified. The DDA75 droplets showed a significant increase in maximum spreading factor (β max) by 37% due to 59% reduction in surface tension. New empirical correlation was developed to predict β max for UWS and DDA75 droplets, which considers the effect of wall temperature on spreading process; the predicted β max values for different liquids including water, hydrocarbon and alternative fuels viz., n-heptane, n-decane, Jatropha biodiesel and camelina-based alternative jet-fuel had a mean error less than 8.2% across all wall temperature conditions. The drop-size distributions of secondary DDA75 droplets revealed considerably narrower drop-size distribution (up to 36%) compared to UWS droplets. The surfactant-added-UWS droplets have the potential to enhance NO x reduction in SCR systems through better evaporation and mixing and also through reduction in the formation of urea deposits.