【作者】 陈旭；

【导师】 何邦全； 郑安国；

【作者基本信息】 天津大学 ， 动力工程（专业学位）， 2016， 硕士

【摘要】 进气道喷射和缸内直喷的独立控制能适时地改变一个工作循环内醇类和汽油的喷油比例,改变不同工况下缸内混合气的分布形式。乙醇和正丁醇是有潜力的内燃机替代燃料。为了揭示乙醇/正丁醇和汽油在不同缸内混合气分层方式下的燃烧耦合关系及其对汽油机的燃烧与排放特性的影响,本文研究了由进气道喷乙醇或正丁醇形成预混醇混合气和缸内直喷汽油形成分层汽油混合气方和不同正丁醇-汽油混合气形成方式下汽油机的燃烧和排放特性。得出以下主要结论:在转速为1500 r/min,进气道喷射正丁醇-汽油直喷(Bu-G)混合气形成方式下汽油机的最佳点火提前角迟于仅采用直喷汽油(GDI)方式下的,但是在固定的循环供油能量下,Bu-G方式下高的正丁醇能量比例(BER)时,汽油机的燃烧稳定性好于GDI下的。随着BER的增加,汽油机的指示热效率逐步增加。在转速为1500 r/min和2000r/min,循环供油总能量为0.65kJ,过量空气系数为1.3时,正丁醇和汽油混合气形成方式对发动机指示效率的影响依赖于BER。当BER为22%时,在进气道喷汽油-直喷正丁醇(G-Bu)方式下汽油机的指示热效率高于Bu-G方式下的。而在BER为66%时,在Bu-G方式下汽油机的指示热效率高于G-Bu方式下的。而在2000r/min和低的BER时,G-Bu方式下汽油机有高的指示热效率。无论是在Bu-G方式还是在G-Bu方式下汽油机的指示热效率均高于GDI方式下。而且随着转速增加,汽油机的燃烧稳定性恶化。在转速为1500 r/min和2000 r/min,循环供油总能量为0.65kJ,过量空气系数为1.1,BER为66%时,在进气道喷乙醇-直喷汽油(E-G)和Bu-G方式下,在直喷汽油压力一定时,在进气冲程中直喷汽油时汽油机的指示热效率和平均指示压力(IMEP)高于在压缩过程中直喷汽油下的。E-G和Bu-G方式下,汽油机的指示热效率,一氧化碳(CO),碳氢化合物(HC)排放都好于GDI方式下的。在转速为1500r/min,循环供油总能量为0.86kJ,过量空气系数为1.1,BER为66%时,进气道喷醇-直喷汽油方式下,提高直喷汽油压力能提高汽油机的指示热效率,并减小循环波动。直喷汽油时刻越早,汽油压力对汽油机的IMEP影响越小。更多还原

【Abstract】 The independent control of port fuel injection(PFI)and direct injection(DI)can timely change the blending ratio of alcohol fuels and gasoline within an operating cycle and thus change the mixture distribution in the cylinder at different engine operating conditions.Ethanol and n-butanol is now recognized as a potential alternative fuel.In order to reveal the coupling relationship between ethanol/n-butanol and gasoline combustion processes when the mixture is formed in different methods and its influence on the combustion and emission characteristics of a gasoline engine,the combustion and emission characteristics of a gasoline engine were investigated when different mixture formation ways of gasoline and ethanol/n-butanol were used with PFI and DI systems.The results show that,At engine speed of 1500 r/min,the optimum spark timing at the maximum brake torque(MBT)is later when n-butanol port injection-gasoline direct injection(Bu-G)is used than when pure gasoline direct injection(GDI)is applied.However,it is found that when a high n-butanol/gasoline energy ratio(BER)is adopted,combustion stability is better than that in the case of GDI.With the increase of BER,the indicated thermal efficiency of the engine increases.At engine speed of 1500 r/min and 2000 r/min,when fueling energy in a cycle is 0.65 kJ and excess air factor is 1.3,BER is an influential factor on the indicated thermal efficiency when different mixture formation methods of n-butanol and gasoline are applied.When BER is 22%,higher indicated thermal efficiency is discovered for the case of gasoline port injection-n-butanol direct injection(G-Bu)mode than that of BuG.However,when BER is increased to 66%,an opposite trend is found.At speed of 2000 r/min,there is a higher indicated thermal efficiency.Both the indicated thermal efficiencies of G-Bu and Bu-G are higher than that of pure GDI.With the increase of speed,combustion stability reduces.At engine speed of 1500 r/min and 2000 r/min,when fueling energy in a cycle is 0.65 kJ,excess air factor is 1.1 and BER is 66%,it is found that higher indicated thermal efficiency and indicated mean effective pressure(IMEP)can be obtained via gasoline injection in the intake stroke than in the compression stroke.Both the strategies of ethanol port injection-gasoline direct injection(E-G)and Bu-G show optimized indicated thermal efficiency,carbon monoxide(CO)and hydro-carbon(HC)emissions compared with pure GDI.At engine speed of 1500 r/min,when fueling energy in a cycle is 0.86 kJ,excess air factor is 1.1 and BER is 66%,higher direct injection pressure results in increased indicated thermal efficiency and reduced cyclic variation for both E-G and Bu-G.The influence of the gasoline injection pressure on the IMEP depends on the injection timing.The earlier the injection timing,the less impact the injection pressure imposes on the IMEP.At speed of 1500 rpm,In alcohol port injection-gasoline direct injection mode,with the increase of gasoline injection pressure,indicated thermal efficiency increases and Coefficient of Variation of IMEP(COVIMEP)reduces.In early gasoline direct injection,gasoline injection pressure have a little impact on IMEP.更多还原