Study On The Influence Of Ignition And Injection System On The Performance Of Methanol-Gasoline Dual-Fuel Rotary Engine

Methanol is considered an ideal alternative fuel for engines due to its high oxygen content,good combustion performance,and clean emissions.The composite injection system can flexibly adjust the injection ratio and injection timing to adapt to different operating conditions,avoiding the disadvantages of methanol fuel such as difficult cold start and fast combustion.Therefore,the application of compound injection system in Wankel engine is the key technology to replace fossil fuel with alcohol fuel in the future.In conclusion,this paper takes a premixed intake Wankel engine as the research object,establishes a CFD numerical calculation model of Wankel engine,and studies the influence of different mixing ratios,ignition timing and composite injection system on the performance of Wankel engine when it is fueled with methanol gasoline.The main research content is as follows:(1)The effect of methanol/gasoline blending ratio on rotary engine was studied.The results show that with the increase of the methanol-gasoline blending ratio,the turbulent kinetic energy of the intake process increases.At the end of the compression stroke,when the blending ratio is 75%and 100%,there is still tumble flow in the combustion chamber.The higher the mixing ratio,the higher the average temperature in the cylinder at the time of ignition,and the higher the pressure in the cylinder.When the mixing ratio is 100%,the temperature in the cylinder at the time of ignition is 8K higher than when the mixing ratio is 0.The mixing ratio has influence on the average pressure in the cylinder and the crankshaft angle and temperature corresponding to the peak pressure.With the increase of methanol-gasoline blending ratio,the increase rate of in-cylinder pressure increases,the crank angle corresponding to the peak pressure advances,and the increase rate of in-cylinder temperature increases.In terms of power performance,methanol-gasoline with medium and low blending ratio has a significant effect on improving the power of the rotary engine,and methanol-gasoline with 50%blending ratio has the most obvious effect on improving the power and torque of the rotary engine;When the mixing ratio is higher than 50%,the effect of improving the power of the rotary engine decreases.In terms of emissions,the higher the blending ratio of methanol and gasoline,the lower the amount of nitrogen oxide.(2)The effect of ignition time on the performance of methanol-gasoline rotary engine was studied.The results show that when the ignition time is delayed,the air velocity in the front of the combustion chamber increases when the rotary engine is ignited.With the increase of the mixing ratio,delaying the ignition time will strengthen the movement intensity of the air flow behind the combustion chamber.When the ignition time is delayed,the volume of the combustion chamber becomes smaller,and the pressure and temperature in the cylinder will rise at this time,which can provide good conditions for initial combustion;The generation of combustion intermediate products(OH)will be delayed with the delay of ignition time,and the generation amount will also decrease,and the distribution range in the cylinder will also become smaller.The ignition time can control the combustion proportion of methanol-gasoline before the top dead center of compression.Delaying the ignition time makes most of the methanol-gasoline fuel burn after the top dead center of compression,reducing the negative compression work generated by premature combustion.The ignition delay period(CA10)and combustion duration(CA90)shorten with the delay of ignition time,but due to the delay of combustion phase,the crankshaft angle corresponding to the combustion center of gravity(CA50)is delayed.Delaying the ignition time can improve the dynamic performance of the rotary engine,and the improvement effect will increase with the increase of the mixing ratio.At the same time,when using methanol gasoline with high mixing ratio,with the delay of the ignition time,low NOx emission can be achieved.To sum up,the ignition time of rotary engine fueled with medium-high mixing ratio methanol gasoline should be close to the TDC of compression.(3)The effect of different intake modes on the combustion of methanol gasoline(M25,M50,M75)with different mixing ratios in a rotary engine was studied.The research shows that the intake mode of combined injection(MPI+GDI)can strengthen the turbulent kinetic energy in the cylinder and keep the increased advantage near the ignition time.When compound injection is adopted,the heat release rate of fuel combustion decreases,the peak pressure in the cylinder decreases,and the crankshaft angle corresponding to the peak pressure is delayed.With the increase of GDI injection ratio,the degree of combustion phase delay increases.After the peak heat release rate of the fuel in the cylinder is delayed to the top dead center,the combustion temperature in the cylinder decreases and the volume fraction of NO_Xdecreases.(4)The influence of GDI location on the intake process,combustion process and emissions was studied.The research shows that the GDI arrangement position will affect the in-cylinder flow.When the GDI arrangement position changes,the number and position of the main vortices at the end of the in-cylinder direct injection are different,and the GDI arrangement position will affect the flow direction and speed of the inlet flow.When GDI is arranged closer to the front of combustion chamber(relative to GDI injection time),the area and mass of spray impinging on the rotor wall will be smaller,and the rich mixture in front of combustion chamber will be more during ignition.The GDI layout position will also affect the engine performance and emissions.When GDI is arranged at the front of the combustion chamber,the cylinder pressure is the most ideal during combustion,but the NO_Xgenerated is also the most.When selecting the GDI nozzle position,it is necessary to consider both emissions and power.