乙醇DI/汽油PFI发动机性能与排放特性

Investigation on Performance and Emissions of Ethanol Direct Injection Plus Gasoline Port Injection Engine

基于一台点燃式发动机,对缸内直喷(DI)乙醇和进气道喷射(PFI)汽油的复合喷射方式进行了研究.与传统喷油模式相比,采用乙醇-汽油复合喷射能够提升发动机动力性.随直喷乙醇比例增加,缸内爆发压力升高;受乙醇燃烧速率和缸内冷却效果的综合影响,着火滞燃期和燃烧持续期先缩短后延长.最佳点火时刻下,单一汽油喷射(PFI和GDI)爆震频次超过10%,,发动机发生轻微爆震,而复合喷射乙醇比例超过20%,可消除爆震;随直喷乙醇比例增加,循环波动系数降低,当量燃油消耗率降低,指示热效率提高,复合喷射相对PFI可提高发动机热效率3.8%,;同时,能够有效降低NOx和HC常规气体排放物.通过采用相对较高的缸内直喷乙醇比例,复合喷射能够提高发动机热效率及抑制爆震并降低常规气体排放物.

A study of dual-fuel injection system,which is composed of gasoline port-fuel injection(PFI)and ethanol direct injection(DI),was performed on a single-cylinder spark-ignition engine.Compared with the traditional injection system,the dual-fuel injection strategy can improve the engine output performance.As the increase of ethanol DI proportion,the maximum cylinder pressure is slightly elevated.The ignition delay and main combustion duration are shortened initially and then expanded due to the comprehensive effect of the relative fast laminar burning speed and the cooling effect of ethanol.At maximum brake torque(MBT)spark timing,slight knocking combustion with a knocking possibility over than 10%,was detected under the case of PFI and GDI.Whereas with more than 20%,ethanol DI,dual-injection could eliminate knocking combustion at all.As DI ethanol ratio increases,the coefficient of variation and the equivalent heat value brake specific fuel consumption decreases.Meanwhile,the indicated thermal efficiency of the engine is improved.The indicated efficiency of G20E80 is 3.8%,,higher than that of the PFI.Simultaneously,regulated gas emissions of NOx and THC become less.With utilization of relative high ethanol DI,dual-injection could gain more benefits in efficiency improvement,knocking suppression and emissions reduction.