HC浓度对EGR冷却器沉积层表面微观结构的影响

Impact of Hydrocarbons Concentration on the Microstructure of Deposit Surface in an EGR Cooler

不同试验条件下沉积在EGR(exhaust gas recirculation)冷却器换热管内表面的颗粒物会形成不同表面微观结构的沉积层。为了量化分析沉积处表面微观结构的分布特征和三维表面的起伏特征,提出采用沉积层表面结构特征面积占比和表面分形盒维数两个参数分析沉积层的表面微观结构变化规律,并利用其分析碳氢化合物(HC,hydrocarbons)浓度对沉积层表面微观结构的影响。结果表明:试验气体中的HC等挥发性物质的析出会影响EGR气体中颗粒物的尺寸,改变沉积层表面凹坑和凸起结构的数量和尺寸分布;随着HC浓度的增加,沉积层表面凸起结构所占的面积百分比逐渐增加,凹坑结构所占面积百分比变化较小;用于表征沉积层表面起伏程度的沉积层表面分形盒维数随试验气体中HC浓度的增加而逐渐增加。

Under different test conditions,the particulate matter deposited on the inner surface of the heat exchange tube of the EGR(Exhaust Gas Recirculation)cooler will form a deposition layer with different surface microstructures.In this paper,two parameters,the characteristic area ratio of the surface structure of the deposition layer and the fractal box dimension number,are used to analyze the effect of hydrocarbons concentration on the deposit surface microstructure.It is found that the precipitation of volatile substances such as hydrocarbons in the exhaust gas would affect the size of particulate in the gas and change the number and size distribution of the deposit surface structure such as concave and convex.Moreover,with the increase of hydrocarbons concentration,the area ratio of convex structure on the deposit surface increases gradually while the area ratio of concave structure changes insignificantly.The fractal box dimension number of the deposit surface increases gradually with the increase of hydrocarbons concentration in the test gas.