Effect Of Fuel Distribution In The Cylinder On The Combustion And Emission Characteristics Of An Engine With Alcohol-gasoline

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.