| Single cylinder diesel engine is the main power source of small agricultural machinery,which has a large amount.The application of clean alternative fuel,coal to F-T(Fischer Tropsch)diesel and methanol in agricultural single cylinder diesel engine,is conducive to promoting the diversification of energy application of diesel engines in China and reducing the emission of pollutants.F-T diesel can be prepared by indirect liquefaction of coal,and its physicochemical properties are different from that of mineral diesel.The combustion process in the cylinder of diesel engine will change due to the mixing of methanol.This paper studies the formation of methanol atmosphere and the combustion process of agricultural single cylinder diesel engine fueled with F-T diesel and methanol by fumigation.The effects of methanol blending ratio,diesel engine working condition and oil supply advance angle on the formation,combustion process and combustion stability of F-T diesel cylinder in methanol atmosphere were studied by means of simulation and diesel engine bench test.F-T diesel has low density and viscosity,high cetane number and is easy to ignite;high methanol oxygen content,high latent heat of vaporization and low cetane number make it difficult to ignite.According to the physical and chemical characteristics of methanol and the characteristics of agricultural 186 FA diesel engine,the fumigation method is used to vaporize methanol,and the gaseous methanol is introduced into the intake pipe to mix with fresh air to form a uniform mixture into the cylinder.The definition of methanol blending ratio was put forward,and the methanol supply system suitable for 186 FA diesel engine was designed.The structure parameters of methanol evaporator,methanol evaporation capacity and control strategy of maximum methanol blending ratio were studied.According to the parameters of intake pipe of 186 FA diesel engine,a three-dimensional model of methanol mixing with air in intake pipe was established by using FLUENT software.The flow field and methanol concentration field in intake pipe were simulated,and the influence of methanol guide pipe structure,installation position and other parameters on methanol air mixing was discussed.The flow field and methanol concentration field of methanol/air mixture under different working conditions were studied.Combined with the parameters of diesel engine speed,power and exhaust temperature measured by bench test,the control strategy of maximum methanol blending ratio is proposed.Based on the structure parameters of 186 FA diesel engine combustion chamber,the combustion process model of F-T diesel engine in methanol atmosphere was established by using fire software.The turbulent velocity field,temperature field and concentration field of F-T diesel were simulated,and the change rule of spray mixing and ignition time of F-T diesel in methanol atmosphere was analyzed.The results show that the F-T diesel is mixed with methanol/air mixture after being injected into the cylinder,and ignites itself at high temperature,which leads to multiple ignition areas,which can lead to the combustion of methanol around.The formation and ignition process of the mixed gas in the cylinder are simulated by adjusting the parameters of methanol blending ratio and oil supply advance angle.The results show that the turbulent energy near the nozzle decreases,the temperature in the cylinder decreases,and the atomization effect of F-T diesel becomes poor,which is not conducive to the formation of the mixture in the cylinder and leads to the delay of ignition time.The advance angle of oil supply increases,the F-T diesel is injected into the cylinder earlier,the peak time of turbulence velocity field near the nozzle is ahead of time,the temperature in the cylinder does not change much,the F-T diesel is mixed with methanol/air,forming a more uniform mixture,and the ignition time is ahead of time.The 186 FA diesel engine test bench was built,and the maximum torque speed of 2700r/min was selected for the test.The indicator diagram of the diesel engine was collected,and the effects of different loads,methanol blending ratio and fuel supply advance angle on the characteristic parameters of combustion process and cycle variation coefficient were studied.The results show that at 2700r/min and 25% load condition,the maximum explosion pressure of diesel engine decreases gradually with the increase of methanol blending ratio.Compared with pure F-T diesel,the maximum explosion pressure decreases by 1.5%,4.5% and 7.0% respectively when the methanol blending ratio is 20%,40% and 60%.The peak value of heat release rate decreases,the average temperature in cylinder decreases,the ignition delay period prolongs,and the combustion duration has no obvious change.At 2700r/min and 75% load condition,with the increase of methanol blending ratio,the peak value of in-cylinder pressure and heat release rate in the cylinder increase,and the average temperature in the cylinder increases.At 2700r/min and 25% load condition,the cyclic variation coefficient of the maximum explosion pressure increases from 5.9%to 9.5% when the methanol blending ratio increases from 20% to 60%;at 75% load condition,the cyclic variation coefficient of the maximum explosion pressure increases from 3.1% to 5.1%,and the combustion stability becomes poor.Under the conditions of 2700r/min,75% load and 60%methanol blending ratio,the fuel supply advance angle was changed,and the variation law of methanol atmosphere F-T diesel combustion process and combustion stability with fuel supply advance angle was discussed.The results show that with the increase of fuel supply advance angle,the peak value of in-cylinder pressure increases,the ignition delay period prolongs,the peak value of heat release rate increases,the average temperature in cylinder slightly increases,and the combustion duration shortens.Compared with the original engine,when the fuel supply advance angle changes,the change of the cyclic variation coefficient of the maximum burst pressure is not obvious.The research content provides a reference for the application of F-T diesel in agricultural single cylinder diesel engine,and it is of great significance to promote the use of methanol in agricultural single cylinder diesel engine,reduce oil consumption and emissions. |
