Combustion Control And Optimization Of A DMDF Engine For Meeting The Emission Legislation Of China Ⅴ

The expanding energy demand,surging oil prices,depleting oil reserves,environmental pollution and climate change problems associated with the utilization of fossil fuels have revived interest to find out clean alternative fuels.Methanol is one of the most competitive alternative fuels due to its liquid nature,high oxygen contents,and high octane number and could produce from renewable sources.In an attempt to overcome the problems,which prevent methanol to be applied to compression ignition engine,such as difficult to auto ignite and evaporate as well as insoluble with diesel fuel,our group has brought out a strategy be known as diesel methanol compound combustion(DMCC).However,the DMCC strategy also encountered challenges of further reduction of the emissions.To overcome the obstacles of combustion controlling and engine out emission reduction for DMCC engine.An engine experimental research has been conducted on a heavy-duty common rail turbocharged Diesel Methanol Dual Fuel(DMDF)engine.With the perspective of mixing process control,air system optimization and transient operation control,engine combustion process control and optimization has been investigated.(a)Pilot injection event would ignite the premixed methanol air mixture,and different injection timing and injection mass would change the level of this effect.In-cylinder mixing process is a dominant process for the combustion,performance and emissions of DMDF engine.As the pilot injection timing is earlier than a certain degree,the pilot heat release process would be diminished.Pilot injection would significantly reduce the NO_x emissions with the penalty of PM.However,with the assistance of post injection event,the penalty of PM would be alleviated.For the multi-injection process,increasing pilot injection fuel mass would increase the NO_x and PM simultaneously.Comparing with single injection strategy,using multi-injection strategy would expand the operation range of DMDF engine.At medium-low load,multi-injection strategy would significantly reduce NO_x emissions,with a penalty of PM.For high load to full load,multi-injection strategy has negligible impact on NO_x but could reduce PM.(b)Intake charge Temperature has a significantly impact on both ignition and heat release process of DMDF engine.As the increase of intake charge temperature,the ignition timing would be advanced.Higher intake charge temperature means higher thermal efficiency.However,if the intake charge temperature excesses a certain level,further increasing intake charge temperature would cause the damage of engine because of the high peak pressure and pressure rise rate.Moreover,with the increase of intake charge temperature,the NO_x and PM increased simultaneously.For the DMDF combustion,the intake charge temperature should be controlled at 40 to 60 ~oC.(c)Reducing AFR would significantly suppress the emissions of NO_x,with penalties of(Brake Thermal Efficiency)BTE and PM.Further air fuel ratio control method could be achieved with the combination of EGR and modification of Turbocharge system,which means even lower NO_x emissions.However,lower NO_xalso caused even more penalties on BTE and PM.For DMDF combustion the NO_xcould be controlled by reducing AFR,however the exponential increased NO_x caused by diesel diffusion combustion process should not be accepted.(d)The current research proposed a combined control strategy of diesel,methanol and EGR correlation.The strategy has been validated and the results show that lack of air charge and excess of EGR is the dominant reason for the excessive PM emissions.For DMDF engines the dynamic operation process could be even more complicated.With the combined control strategy,the PM emissions at transient operation conditions has been successfully reduced,with a small penalty of NO_x.(e)An artificial neural network(ANN)and genetic algorithm(GA)based optimization method has been investigated.DMDF has much more complicated trade-off relation with various emissions and control parameters.In an attempt to sovle this problem,an ANN and GA based optization method has been established.Based on the results of the simulations,the full MAP of DMDF operation has been calibrated.The results show that after the calibration,average methanol energy fraction has excess 40%with a significant reduction of NO_x.Finally,China V emission test has been passed just with a small penalty of thermal efficiency at low load operation points.