氢燃料内燃机NOx排放特性及机理

为深入研究氢燃料内燃机NO_x的生成机理,基于CONVERGE软件建立了三维网格耦合详细化学反应机理的氢燃料内燃机CFD仿真模型,进行了氢燃料内燃机在不同负荷下的燃烧及排放特性研究。模型的仿真结果和试验数据较为吻合。结果表明,氢气浓度增大有利于提高氢燃料内燃机的效率;NO的大量生成出现在不断升温的快速燃烧期,快速燃烧结束后NO总量不断减少,其缸内平均温度低于2 200K时NO总量趋于稳定;热NO,NNH和N_2O是NO生成最主要的路径,其中热NO路径产生的NO排放最多,其贡献率随着负荷增大而增大。NNH和N_2O路径在较低浓度时有接近25%的贡献率,而在燃空当量比为1.0时,这2种路径对NO生成的贡献率之和为负值。采用化学反应动力学方法得到了3种路径在不同负荷下对NO生成的贡献率,初步揭示了氢燃料内燃机NO_x生成的机理,为后续研究提供了理论参考。

Characteristics and mechanism of NOx emission of hydrogen fueled internal combustion engine

In order to deeply study the NO_x formation mechanism of hydrogen fueled internal combustion engine (HICE), a hydrogen fueled internal combustion engine CFD simulation model including three-dimensional gridding coupling detailed chemical reaction mechanism is built based on CONVERGE software, and the combustion and emission characteristics of hydrogen fueled internal combustion engine under different loads are researched. The simulation result is consistent with the experimental data. The simulation results show that the increasing concentration of hydrogen is beneficial to improving the efficiency of hydrogen fuel internal combustion engine. The large amount of NO generates in the rapid combustion period, the total amount of NO decreases constantly after the rapid combustion period, and the total amount of NO tends to be stable when the average temperature is below 2 200 K. NO is generated mainly through three paths including thermo NO, NNH and N₂O, and the thermo NO path contributes a large proportion of total NO emissions, whose contribution ratio increases with the increase of fuel-air equivalence ratio. NNH and N₂O contribute about 25% of total NO emissions at lower concentrations, while when fuel-air equivalence ratio is 1.0, the sum of the contributions of these two paths to NO generation is negative. The contribution ratios for NO generation of three paths under different loads are obtained using chemical reaction kinetics method, which can reveal the NO_x generation mechanism of hydrogen fuel internal combustion engine and establish the theoretical foundation for subsequent study.