废气再循环对柴油机排气颗粒挥发与氧化特性的影响

The Effects of Exhaust Gas Recirculation on the Volatilization and Oxidation Characteristics of Particles from Diesel Engine

应用热重分析仪,在N2和O2氛围下,分别对不同EGR率(0,10%和30%)下采集的柴油机排气颗粒进行热重试验。结果表明,在N2氛围下,随着EGR率的增加,颗粒样品的失重质量逐渐减小,质量变化率峰值逐渐降低,对应温度有所升高;颗粒中含水百分率和soot含量升高;而SOF组分含量降低。在O2氛围下,SOF的变化规律与N2氛围下基本相同,但质量变化率峰值有所增加,对应温度有所降低;在soot氧化阶段,soot分解开始时刻温度降低,失重质量和质量变化率峰值均有较大幅度提高;随着EGR率的增加,颗粒中soot的质量变化率峰值逐渐增加,但对应的温度较高,且颗粒活化能增加,说明随着EGR率增加,颗粒的表面官能团和表面活性减小,达到质量变化率峰值所需的能量较大,颗粒不易被氧化分解;同时,颗粒的燃烧特性指数和燃尽特性指数均呈下降趋势,导致颗粒不易被完全燃烧,燃烧性能变差,燃烧效率降低。

Thermo gravimetric tests are conducted on the particles collected under different EGR rate （0%,10%,and 30%） in both atmospheres of N2 and O 2 by using thermo gravimetric analyzer. The results show that in N2 atmosphere,with the increase of EGR rate,both mass losses and the peak mass changing rate of particle sample gradually reduce,and the corresponding temperature rises. The contents of moisture and soot in particle increase while the content of SOF constituent deceases. In O 2 atmosphere,the changing pattern of SOF is basically the same as in N2 atmosphere,but the peak mass changing rate rises and the corresponding temperature lowers. In soot oxidation phase,the temperature at the start moment of soot pyrolysis lowers and both mass loss and the peak mass changing rate have an evident rise. With the increase of EGR rate,the peak mass changing rate of soot gradually rises but the corresponding temperature is relatively high,while the activation energy of particles increases,meaning that when EGR rate is going up,the surface functional group and activity of particles reduce,the energy needed for reaching the peak mass changing rate is relatively significant,and the particles are difficult to be oxidized and pyro lyzed. In addition,both the burning and burnout characteristic indices of particles tend to fall,resulting in the incomplete combustion with deterioration in combustion performance and efficiency of particles.