为改善柴油微引燃双燃料发动机的燃烧过程、经济性及排放特性,通过数值仿真方法研究了大负荷工况下喷油策略、废气再循环(Exhaust Gas Recirculation,EGR)及进气门晚关(Late Intake Valve Closing,LIVC)对柴油微引燃双燃料发动机缸内燃烧及排放特性的影响.结果显示:随着预喷时刻提前,缸压和放热率峰值降低,NOx排放量降低,但预喷时刻过早导致缸内燃烧状况恶化,热效率下降.随着主喷时刻提前,缸压和放热率峰值先升高后逐渐降低,碳烟、碳氢化合物(Hydrocarbon,HC)和CO排放量先逐渐降低后略微升高,NOx排放量先增多后减少;燃烧相位受主喷时刻的影响较大,合理调节主喷时刻可有效控制天然气/柴油反应活性控制压燃(Reactivity Controlled Compression Ignition,RCCI)燃烧相位和污染物排放.随着EGR率增加,缸压及放热率峰值减小,缸内温度降低,燃烧相位推迟,有利于发动机向更高负荷范围拓展.当进气门晚关角度为0时,EGR率从32％增至48％,NOx排放量下降66.21％;当EGR率大于40％后,碳烟、HC和CO排放量随EGR率增加而急剧升高.随着LIVC增大,缸压峰值和放热率峰值显著下降,指示热效率和NOx排放量逐渐降低,碳烟、HC和CO排放量增加.在大负荷工况下,采用合适的主喷时刻、较小的LIVC耦合较低的EGR率可提高发动机的热效率,维持NOx排放量较低的同时能有效减少碳烟、HC和CO排放量.
Study on combustion and emission characteristics of diesel micro-ignition dual-fuel engine
To further improve the combustion and emission performances of diesel micro-ignition dual-fuel engines to meet increasingly stringent emission regulation,the combined effects of fuel injection strategies,Exhaust Gas Recirculation(EGR),and Late Intake Valve Closing(LIVC)on the combustion process,performance,and emission characteristic in a natural gas/diesel Reactivity Controlled Compression Ignition(RCCI)engine was numerically studied.The results showed that the maximum cylinder pressure,peak heat release rate,and NOx emissions are found to decrease with advanced split injection timings.However,too advanced split injection timing can lead to poor combustion performances and a strong decrease in thermal efficiency.With advanced main injection timing,the maximum cylinder pressure and heat release rate gradually increased and then decreased,the opacity smoke,HC,and CO emissions gradually decreased and then increased slightly,while the NOx emission gradually increased and then reduced.The main injection timing has a more significant impact on the combustion phase.Proper adjustment of the main injection timing is important in the control of the combustion phase and pollutant emissions in natural gas/diesel RCCI engines.With an increase in EGR rate,the maximum cylinder pressure and heat release rate reduced,the gas temperature in the cylinder decreased,and the combustion phase significantly retarded.A higher EGR rate was beneficial for the engine to extend RCCI operating towards a higher load range.With the EGR rate increased from 32％to 48％with LIVC at 0,the NOx emission was reduced by 66.21％.However,the opacity smoke,HC,and CO emissions sharply increased when the EGR rate was more than 40％.With the increase of LIVC,the maximum cylinder pressure and heat release rate decreased,and the indicated thermal efficiency and NOx emissions gradually reduced,while the opacity of smoke,HC,and CO emissions increased.The analysis of critical parameters suggests that the optimum main injection timing,smaller LIVC coupled with a lower EGR rate can significantly improve the thermal efficiency,and effectively reduce the opacity smoke,HC,and CO emissions while maintaining lower NOx emissions of the RCCI engine at high load conditions.
environmental engineeringemissioncombustioninjection strategyExhaust Gas Recirculation(EGR)Late Intake Valve Closing(LIVC)
NETL
NSTL
万方数据
