富氧燃烧对柴油机低温燃烧反应机理影响的数值分析

从柴油机缸内燃烧反应的化学反应动力学机理出发,利用CHEMKIN软件对富氧燃烧时的低温反应进行了研究,运用计算流体动力学分析方法,通过耦合柴油机三维燃烧模型和正庚烷氧化反应动力学模型对低温反应机理中重要的脱氢反应和加氧反应过程进行了数值分析.对比空气助燃、富氧浓度对脱氢反应和加氧反应的影响发现:富氧燃烧能够促进脱氢反应,在压缩的上止点时刻,氧的体积分数分别为23%、25%和27%时的缸内脱氢产物C7H15的质量分数最大值分别是空气助燃时的1.95倍、4.77倍和291.58倍;加氧反应的速率随富氧浓度的升高呈线性增长趋势;富氧燃烧可以提高柴油机的热效率,使缸内生成更多的OH自由基,从而加快了后续的中温反应和高温反应速度.

Numerical Analysis on Effects of Oxygen-Enriched Combustion on Low-Temperature Reaction Mechanism of Diesel Engine

From the chemical reaction kinetics of diesel engine combustion,the investigation into the low-temperature reaction of oxygen-enriched combustion was done by CHEMKIN.Two important low-temperature reactions,the dehydrogenation reaction and the oxygen-addition reaction,were numerically analyzed by the CFD three-dimensional combustion model coupled with the N-heptane oxidation kinetic model.The results show that oxygen-enriched combustion can promote the dehydrogenation reaction.At the compression TDC,the maximum mass fraction of C7H15produced by the dehydrogenation reaction in the oxygen-enriched combustion is 1.95 times,4.77 times and 291.58 times of in the ordinary combustion when the oxygen concentration is 23%,25% and 27%,respectively.The oxygen-addition reaction rate increases linearly with an increase in the oxygen concentration.In addition,oxygen-enriched combustion enhances the diesel engine thermal efficiency and generates more OH radicals,and accelerating the subsequent reactions at medium temperature and high temperature.