Simulation Study On Combustion And Emission Of Compression Ignition Methanol Engine

Methanol is a good clean alternative fuel,and the promotion of methanol engine is in line with China’s energy structure and carbon neutral environmental protection concept.In traditional diesel engine,increasing intake pressure can improve power and reduce NOx emission,increasing compression ratio can improve power performance and economy,and changing nozzle layout can better organize combustion.In order to provide theoretical guidance and direction for operation parameter optimization of glow plug combustion supporting methanol engine,a three cylinder diesel engine was transformed into a pure methanol engine with glow plug combustion supporting,A three-dimensional full port model was established to study the combustion and emission characteristics with different inlet pressure,compression ratio,nozzle layout and pre injection timingUnder the condition of constant injection parameters,the increase of intake pressure can improve the thermal efficiency of the engine,optimize the power performance and economy,and advance the combustion process as a whole.The maximum combustion temperature can be effectively reduced and the formation of NOx can be inhibited under the premise of keeping the intake temperature unchanged.However,the low temperature combustion can not oxidize the generated root and HC,and the amount of NOx is increased.CO reaches the lowest value at 0.12mpa inlet pressure.Under the four compression ratios of 17,18,19 and 20,the compression ratio of the original engine 19 has the highest thermal efficiency.Although increasing the compression ratio makes the whole combustion process move forward and the peak cylinder pressure increase,the combustion before TDC does negative work.At high compression ratio,the combustion temperature is high and the NOx emission is high,but the emissions generated by the earlier combustion are oxidized by high temperature,and the emissions of root and HC are reduced by full combustion,while the low temperature in the later combustion makes the generated CO unable to be oxidized.Under the premise that the total area of the nozzle is unchanged,the 10 hole homogeneous nozzle has the highest thermal efficiency,while the flame propagation anomaly of the non-uniform nozzle leads to its low thermal efficiency,increasing the number of nozzle holes,increasing the reaction area of the oil mist and air,reducing the penetration distance of the spray,resulting in an increase in NO_X emissions,but the HC emission is basically 0,and the generated SOOT and CO increase.The 6-hole uniform distribution nozzle is the best.The pre injection timing of-30°CA ATDC has the highest thermal efficiency.The pre injection strategy can effectively reduce the pressure rise rate and improve the thermal efficiency,but the emission is inferior to the single injection.Among the four kinds of pre injection timing,NOx decreases with the delay of pre injection timing,and the lack of oxygen in the cylinder at the end of pre injection combustion causes the rise of root and CO.The residence time and combustion duration of single injection methanol are the shortest,so its emission is the best.