【作者】

Wanhua Su

【摘要】

论文已在中国上海举行的第27届CIMAC大会上发表。论文的版权归CIMAC所有。 In this study, experimental and simulated investigations on the effects of charge density(p tdc), temperature(Ttdc) and oxygen concentration(9 O2) on the emissions and thermal efficiency of high brake mean effective pressure(BMEP) diesel engines were conducted. Experimental studies were conducted in a modified single cylinder engine equipped with variable mechanisms of boost, exhaust gas recirculation(EGR), intake valve closing timing(IVCT)and a flexible fuel injection system to regulate the p tdc,p O2 and Ttdc. Simulations of engine combustion processes were performed with an ECFM-3Z combustion model. The results revealed that higherp tdc, leading to lower overall fuel/oxygen equivalence ratio, enhanced the rate of mixing and chemical reaction and benefited improvement of the thermal efficiency. It was found that increasing charge density played two opposite roles in NOx formation: one was inhibiting combustion temperature rise due to in-creased total heat capacity of the charge and another was increasing the mixing rate. The role of less EGR ratio used in high brake mean pressure (BMEP) was essentially to decrease mixing rate of fuel and oxygen and then the chemical reactivity of the fuel/gas mixture. Higher charge density, combined withmoderate EGR ratio, resulted in decreasing over rich mixture(Φ>2) due to increased mixing rate with higher charge density and reserving the in burning fuel as incomplete combustion products CO in beginning phase of combustion, because a larger amount of richer mixture(local equivalence ratio 2>Φ>1) was formed due to relatively lower mixing rate with the existing EGR gas. Thereby the soot formation rate was drastically reduced. Higher charge density combined with moderate EGR ratio led to a retardation of the rate of heat release(ROHR),a reduction of the tempera-ture of combustion gases(Tb) and the high temperature abidance scale(HTAS), which was defined in this study as a measurement of mass averaged temperature in the cylinder, decreased NO, emissions. And it was confirmed that finally exhaust soot depends on the later phase burning rate of CO formed in combustion first phase as mentioned above. The reduction in the temperature at the top dead center Ttdc was realized by retarding IVCT, which was proved to be an effective strategy for controlling combustion in high BMEP-clean diesel engines at meddle-full loads operating conditions. Keywords: High BMEP diesel en-gine; Combustion path; Emissions, Efficiency, Charge density; Oxygen concentration; LTC-Diesel

【会议名称】

第27届CIMAC会议

【会议地点】

上海

【下载次数】

1

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