纯氢内燃机氮氧化物排放机内净化的仿真研究

Simulation of Inner-Engine NOx Emission Control on Pure Hydrogen Engines

摘要:

纯氢内燃机工作时不会产生一氧化碳、碳氢化合物等有害排放物，但会面临高氮氧化物排放的问题，而机内净化和机外净化是控制氮氧化物排放的两种常用手段。机外净化主要通过成熟的选择性催化还原（SCR）技术降低氮氧化物排放，但机内净化技术目前还很少被关注。为此，采用Chemkin Pro软件中的闭口均质反应器模型来模拟纯氢内燃机氮氧化物排放的机内净化。结果显示，废气再循环（EGR）技术可以降低氮氧化物排放，当EGR率为20%时，氮氧化物排放降低了45.3%，但仅使用EGR来降低氮氧化物排放的效果还不够明显，氮氧化物排放依然很高。与单独应用EGR技术相比，EGR技术与稀薄燃烧技术相结合能够更好地实现氮氧化物排放控制，如过量空气系数为1.4、EGR率为20%时，氮氧化物排放量降低了96.31%，实现了纯氢发动机的超低排放。与EGR技术以及EGR?稀薄燃烧技术相比，内部选择性非催化还原技术的氮氧化物排放控制效果更佳，仅10%的氨气比例就能使纯氢发动机氮氧化物排放降低96.32%，15%的氨气比例可以实现纯氢发动机氮氧化物零排放，且并不需要EGR或稀薄燃烧技术的参与；然而，精确控制发动机缸内氨气比例是十分必要的，否则会产生残氨排放污染环境。

Abstract:

Hydrogen is an ideal engine fuel. Pure hydrogen engines do not produce CO and HC emissions but face the high NOx emission problem. Inner-engine control and outer-engine control are two ways to decrease the NO_x emission. Outer-engine control mainly reduce NO_x emission through selective catalytic reduction （SCR）， which has been well studied. However， there are few studies on NO_x emission control of pure hydrogen engines through inner-engine control. In this paper， the closed homogeneous reactor （CHR） in Chemkin Pro was used to simulate the main inner-engine NO_x emission control in pure hydrogen engines. The results show that single exhaust gas recirculation （EGR） decreases NO_x emission by 45.3% at an EGR ratio of 20%， indicating that the NO_x emission is not significantly reduced. However， EGR plus lean-burn decreases NO_x emission by 96.31% at a λ of 1.4 and an EGR ratio of 20%， achieving ultra-low NO_x emission of pure hydrogen engines. Compared with single EGR and EGR plus lean-burn， SNCR are better for NO_x emission control. A NH₃ ratio of only 10% can decrease NO_x emission by 96.32% on pure hydrogen engines， while a NH₃ ratio of 15% can achieve zero NO_x emission on pure hydrogen engines without a large λ value and EGR ratio. However， it is necessary to accurately control the NH₃ ratio in the cylinder， otherwise it is easy to produce residual NH₃ which can pollute the environment.