后喷射和正丁醇对柴油机碳烟影响的数值模拟

Numerical Simulation on the Effects of Post Injection and n-Butanol on Soot Emission of Diesel Engine

采用CFD计算程序耦合正庚烷-正丁醇-多环芳烃简化动力学模型,并结合多步现象学碳烟生成模型,研究了在将NOx控制在2.0g/(kW·h)情况下后喷射和含氧燃料正丁醇对碳烟生成过程和排放的影响.结果表明,后喷射提高燃烧后期温度、增强碳烟氧化和增强燃烧后期缸内充量运动,是其降低碳烟排放的主要原因;正丁醇降低碳烟排放主要是通过降低碳烟前驱物多环芳烃浓度和增强油气混合过程即降低当量比实现的.在后喷射基础上应用含氧燃料正丁醇,可以在NOx排放保持不变的前提下大幅度将碳烟排放(0.032g/(kW·h)降低至0.0073g/(kW·h)).因此采用多次喷射耦合EGR结合含氧燃料正丁醇,是降低柴油机排放的有效技术途径,可以显著改善柴油机碳烟排放.

Numerical simulation have been conducted to explore the effects of post injection and n-butanol on the combustion process and soot emissions of diesel engine with NOx kept at 2.0 g/（kW · h）. A reduced n-heptane-n- butanol-polycyclic aromatic hydrocarbon（PAH） mechanism was coupled with the computational fluid dynamics （CFD） code, and the soot emissions were predicted by a multi-step phenomenological soot model. The results show that soot emission can be greatly reduced by applying post injection, which can be attributed to the higher tempera- ture, accelerated soot oxidation process, and enhanced in-cylinder air motion brought by post injection; that the soot precursor PAH and the equivalence ratio can be effectively reduced by n-butanol through the oxygen in the mole- cule and the enhanced fuel-air mixing process, thus soot emission reduction can be achieved. By applying post injec- tion coupling exhaust gas recirculation （EGR）, combined with n-butanol, the soot emission can be reduced from 0.032 g/（kW · h） to 0.007 3 g/（kW · h） when NOx is kept at 2.0 g/（kW · h）. Therefore, it is one of the competitive control strategies to realize high efficiency and clean diesel combustion.