富燃条件下等离子体活性粒子对乙烯点火影响机理分析

Mechanism Analysis of Plasma Active Particles Effects on Ethylene Ignition Under Rich Burn Condition

为探究富燃当量比条件下,等离子体对乙烯/空气混合气体点火延时影响及其化学动力学机理,采用敏感性分析与化学反应速率方法,分析了当量比1.0、1.5、2.03种条件下,不同浓度的H、O原子对乙烯/空气混合气体点火延时影响机理。研究结果表明,在0.1 MPa、1000 K环境条件下,当量比不变,添加H原子浓度越高,乙烯/空气点火延时越短,点火延时最大降低99.5%;O原子也能缩短乙烯/空气点火延时,最小点火延时仅为添加相同浓度H原子后的1/3。与无等离子体工况不同,在当量比不同但添加相同浓度活性粒子条件下,随着活性粒子浓度的增加,乙烯/空气点火延时伴随当量比的提高出现了先降低后增加的变化。添加摩尔分数2.0%的H原子后,与最低点火延时1.5×10^-4 s相比,当量比的提高使得点火延时分别增加7.3%、18.4%。添加摩尔分数2.0%的O原子后,与最低点火延时4.8×10^-5 s相比,随着当量比提高,点火延时分别增加14.0%、32.9%。H原子主要通过直接影响反应H+O2=O+OH、H+O2(+M)=HO2(+M)缩短点火延时;O原子则是通过直接影响反应C2H4+O=CH2CHO+H,从而加速H原子的生成,促进链传递反应H+O2=O+OH、HO2+H=2OH化学反应速率,缩短乙烯/空气混合气体点火延时。

To investigate the influence and kinetic mechanism of plasma on the ignition delay of the ethylene/air mixture under rich burn condition,the sensitivity analysis and rate of production method were adopted to analyze the mechanism of ethylene/air ignition delay with different concentrations of H and O atoms under equivalence ratios of 1.0,1.5 and 2.0.The results show that,under the conditions of 0.1 MPa and 1000 K with constant equivalence ratio,the higher the concentration of H atom is added,the shorter the ignition delay of ethylene/air will be,and the maximum ignition delay reduces by 99.5%.O atoms can also shorten the ignition delay of ethylene/air,the minimum ignition delay is only 1/3compared with adding the same concentration of H atoms.Different with the condition of no plasma,under the conditions of different equivalence ratios but in the same concentration of active particles,the ethylene/air ignition delay decreases first and then increases with the elevation of equivalence ratio as the concentration of active particles increases.Compared with the minimum ignition delay of 1.5×10^-4 s,after adding 2.0%H atom,the increase of equivalence ratio will cause the ignition delay to increase by 7.3%,18.4%,respectively.When adding 2.0%O atom,compared with the minimum ignition delay of 4.8×10^-5 s,the ignition ratio will increase by 14.0%,32.9%respectively with elevation of equivalence ratio.The H atom mainly shortens the ignition delay by directly affecting the reaction H+O2=O+OH,H+O2(+M)=HO2(+M);The O atom accelerates the formation of H atoms by affecting the reaction C2H4+O=CH2CHO+H,and promotes reaction rates of the chain transfer reaction H+O2=O+OH,HO2+H=2OH to shorten the ethylene/air ignition delay.