Experimental Study On Combustion And Emission Of Methanol Gasoline Engine With Combined Injection

Based on the energy structure of"rich coal,lack of oil and less gas",methanol,which has a wide range of resources,low price and excellent physical and chemical characteristics,provides a practical solution for alleviating the shortage of oil resources and exhaust gas pollution in China.In this paper,methanol and gasoline were used in the internal combustion engine with the combined injection technology.Two injection modes of GPI+MDI and MPI+GDI were adopted to study the effect of methanol/gasoline combined injection on engine cylinder combustion,conventional gas emission and particulate emission.The conclusions are summarized as follows:The comparative analysis of GPI+MDI and MPI+GDI injection modes at different operating conditions shows that the engine output torque,peak cylinder pressure and peak heat release rate increase with the increase of methanol ratio,moreover,the phase of peak cylinder pressure and the phase of peak heat release rate advance,which is not limited by the engine operating conditions.Compared with MPI+GDI,GPI+MDI injection mode is better at improving combustion and improving power performance.The increase of methanol content in the two injection modes can effectively reduce HC and CO emissions,and the emission of HC and CO in GPI+MDI injection mode is lower than that in MPI+GDI injection mode when pure methanol is used.In terms of NOx emission,the two injection modes show different trends.The NOx emission of MPI+GDI injection mode decreases continuously with the increase of methanol proportion,while GPI+MDI injection mode shows the trend of first decreasing and then increasing.Under the two injection modes,the addition of methanol can greatly reduce the particulate emissions of GDI engine.When the proportion of methanol is more than 60%,almost no particulate emissions are generated.In the particle size distribution,there are some differences between the two injection modes.When the methanol ratio is small,GPI+MDI injection mode mainly presents a single peak distribution of nuclear state,while MPI+GDI injection mode presents a double peak distribution of nuclear state and accumulation state.Compared with MPI+GDI,GPI+MDI injection mode is more effective in reducing particulate emissions.Focusing on the GPI+MDI injection mode with better combustion and emission performance,it was found that with the advance of the ignition timing,the engine torque increases first and then decreases,and the flame propagation rate is increased after the use of methanol,the MBT point of pure methanol is 2-3°CA later than that of pure gasoline.HC and NO_X emissions continue to increase with ignition advance,while CO shows a trend of first increasing and then decreasing.At a smaller ignition advance angle,as the proportion of methanol increases,HC,CO,and NO_X emissions gradually decrease;when the ignition advance angle is too large,the excessive methanol content causes HC and NO_X emissions to rise again.The nuclear mode particulate number,the accumulation mode particulate number,and the total particulate number gradually increase with the advance of ignition.When the fuel is pure gasoline,the TPN when the ignition advance angle is 25°CA BTDC is 2.7 times higher than that of 5°CA BTDC.For the study of excess air coefficient in the current range,with the increase of excess air coefficient,the flame development period and flame propagation period are gradually extended,and the COV_IMEP is gradually increased.The increase of methanol ratio is helpful to shorten the flame development period and improve combustion stability,while the flame propagation period shows a trend of first shortening and then increasing.With the increase of the methanol energy fraction,NOx emissions first decrease and then increase when?=1 and?=1.1,while NOx emissions continue to decrease when?=1.2.Nuclear particles occupy the leading position in particulate emissions.The increase of excess air coefficient makes the the nuclear mode particulate number,the accumulation mode particulate number,and the total particulate number decrease rapidly,the total particulate number at?=1.2 was reduced by about 50%compared with that at?=1.Combined injection with methanol content higher than 60%can make the particle drop more than 95%.