【摘要】 将D19共轨柴油机的一维仿真模型与正庚烷简化机理耦合,计算不同EGR率下缸内进气组分的质量分数,以此为初始条件,利用三维CFD模拟,研究EGR的三种效应各自对燃烧及排放的影响以及三效应间的相互关系.结果表明:EGR的稀释效应是降低缸内压力、温度和累积放热量,推迟燃烧相位的主因,同时也决定着CO与NO的排放终值;由稀释效应引起的低温、缺氧抑制NO的生成,其中低温比缺氧的影响更强,并会削弱H₂O和CO₂的热效应对NO的抑制作用;对于EGR热效应而言,单位物质的量浓度CO₂吸热作用约是H₂O的4倍;碳烟排放在中等EGR率时主要受稀释效应影响,在高EGR率时,受三效应共同影响呈现低生成、弱氧化的变化趋势.更多还原

【Abstract】 One-dimensional simulation model of D19 common rail diesel engine is coupled with simplified n-heptane mechanism,and the mass fraction of in-cylinder inlet components is calculated under different EGR ratios.With the above as the initial conditions,three effects of EGR on combustion,emissions and their relationships are studied using three-dimensional CFD numerical simulation.Calculation results show that the dilution effect of EGR is the main factor in lowering in-cylinder pressure,temperature,cumulative heat release and delaying combustion phase,and it also determines the final emissions of CO and NO.In addition,low temperature and hypoxia caused by dilution effect inhibit NO generation.Compared with hypoxia,low temperature has greater effect,which also weakens the thermal effect of H2 O and CO₂ to inhibit the production of NO.In terms of thermal effect,heat-absorbing effect of CO₂ is about four times that of H2 O in unit molar concentration.At middle EGR ratio,soot emission is mainly influenced by dilution effect,while at high EGR ratio,it is mainly influenced by three effects working together,which presents the tendency of low generation and weak oxidization.更多还原