乙炔/空气预混火焰中CO添加对炭黑生成影响的数值分析

摘要

针对乙炔/空气预混火焰中CO添加对炭黑生成的影响进行了详细的数值模拟.通过对含有不同CO添加量的火焰的模拟结果比较,研究CO添加的温度和化学作用对于炭黑形成的影响.计算结果显示CO添加使炭黑的生成单调下降.炭黑体积分数和成核速率随着温度的升高而增加,到达一个阈值后,再随温度的升高而减少.从炭黑生成的H-萃取角度来看,由于反应OH+CO=CO2+H的向右速率增加,H原子增加以及OH自由基减少,CO添加会激发炭黑生成.从炭黑生成的C-添加机理来看,CO添加减小了C2H2的消耗速率,CO添加也有助于炭黑生成,但CO添加降低了燃料中C2H2的体积分数,使得炭黑表面增长速率降低.%The effect of carbon monoxide addition on soot formation in an acetylene/air premixed flame was investigated by detailed numerical simulation.This work focused on both the temperature effect and chemical effect of carbon monoxide addition on soot formation by comparing the results of flames with different CO contents.We find that the addition of carbon monoxide consistently reduces the formation of soot.The soot volume fraction and nucleation rate increase until a threshold temperature is reached and then decrease as the temperature increases.Considering that soot formation took place at the active site by H-abstraction mechanism,the addition of CO promotes the formation of soot.The concentration of H radicals increases and the concentration of OH radicals decreases because of the increased forward rate of the reaction OH+CO=CO2+H.For soot formation to occur by the C-addition mechanism,the degradation rates of C2H2 tends to decrease and this promotes the formation of soot along with CO addition.On the other hand,the addition of CO 5-greatly reduce the volume fraction of C2H2 in fuel resulting in a lower surface growth rate.