富氢重整气对天然气发动机燃烧反应过程的影响

Effects of Hydrogen-Rich Reformed Gas on the Combustion Reaction Process in a Natural Gas Engine

为研究基于废气重整再循环(REGR)技术的天然气发动机燃烧排放调控机制,开展了富氢重整气添加对点燃式天然气发动机缸内燃烧过程影响的数值模拟研究。结果表明,添加富氢重整气与增大过量空气系数对天然气发动机的燃烧过程的影响规律相反。增大重整气添加率可使燃料着火时刻提前1.42°,燃烧持续期缩短;增大过量空气系数则会使缸内平均压力峰值和放热率峰值降低,着火时刻滞后2.24°。REGR率增加到16%时可使总碳氢化合物排放降低26.98%,NO x排放降低62.52%,但会导致发动机功率降低9.52%。基于此,从化学动力学角度进一步解析REGR率对天然气发动机缸内燃料燃烧反应过程与污染物生成演化过程的影响。结果表明,随REGR率增大,OH自由基参与CH 4消耗反应占比增大,从而加快基元反应速率,使燃烧相位提前,并使未燃HC排放降低。

To investigate the regulation mechanism of reformed exhaust gas recirculation(REGR)technology on the combustion and emission of natural gas engines,a numerical simulation study on the combustion process of the spark-ignition natural gas engine was conducted.The results show that the effects of hydrogen-rich reformed gas addition on the combustion process of natural gas engines are inverse to that of increasing excess air coefficient.Specifically,the ignition time of fuel advances by 1.42°and the combustion duration is shortened with the increase of the reformed gas addition rate(REGR rate).However,with the increase of excess air coefficient,the in-cylinder pressure and the heat release rate both decrease,and also,the ignition time is delayed by 2.24°.When REGR rate increases by 16%,the total hydrocarbon(THC)and NO x emission are reduced by 26.98%and 62.52%,respectively;but the engine power will be reduced by 9.52%.Thereout,the influences of REGR rate on the fuel combustion process and pollutant formation process of liquefied natural gas engines were further analyzed from the perspective of chemical kinetics.It shows that the proportion of OH radical participating in CH 4 consumption reaction increases with the REGR rate.Consequently,the combustion phase is advanced by accelerating the elementary reaction rate,and the unburned HC emission is reduced as well.