柴油机排气颗粒的结构特征

Structure characteristics of diesel engine exhaust particles

为研究柴油机排气管内颗粒的微观结构及其变化规律,运用Fluent软件模拟186F柴油机排气管内废气温度、压力、流速的变化趋势,并采集柴油机排气管不同位置的颗粒,采用高倍透射电镜分析颗粒的微晶结构特征的变化规律.结果表明:排气管内压力最高达0.3MPa,温度由500℃降至400℃时,排气弯管附近的气流运动方向发生反弹;随着颗粒运动,其基本碳粒子的微晶碳层排列结构趋于无序,内核与外壳边界逐渐模糊;颗粒从排气管进口运动3m后,微晶尺寸减小约19.6%,颗粒弯曲度增大约15.0%,分形维数逐渐减小,颗粒结构疏松,更容易被氧化.

In order to study the microstructure and variation of particles in diesel engine exhaust pipe,the variety of temperature,pressure and flow velocity of exhaust gas in the exhaust pipe of 186F diesel engine are calculated based on Fluent.The particles at different positions in the diesel exhaust pipe are collected and analyzed by high power projective electron microscope.The results show that the air flow direction is rebounded near the exhaust pipe when the pressure in the exhaust pipe is high up to 0.3 MPa and the temperature reduced from 500℃to 400℃.In the process of diesel engine exhaust transport,the arrangement of microcrystalline carbon layer of granular carbon particles tends to be disordered,the crystallite average size becomes smaller,and the boundary between core and shell tends to be fuzzy.When particles move 3 m from the intake,the microcrystalline size decreases by about 19.6%,the curvature of the particles increases by about 15.0%and the fractal dimension decreases gradually.The structure of the particles is looser and easier