Research On Combustion Process And Emission Characteristics Of High Compression Ratio Spark Ignition Methanol Engine

As petroleum resources decrease and climate warming becomes a major environmental issue,the search for alternative fuels is imminent.Methanol has attracted wide attention due to its advantages such as high oxygen content,sufficient combustion,high octane number,good anti-knock performance,and various preparation methods.It is considered to be one of China's most promising alternative fuels for automobile engines in the future.In this paper,a one-dimensional and three-dimensional simulation model of a high compression ratio methanol engine is established based on a modified engine of a diesel engine.The effects of EGR,initial flame kernel radius,equivalent ratio and compression ratio on the combustion process and emissions of high compression ratio spark-ignition methanol engines were analyzed.Combined with the detailed chemical reaction kinetics mechanism,the effect of EGR on the knocking combustion of high compression ratio spark-ignition methanol engines was analyzed,and the anti-knock performance of common high-octane alternative fuels methanol,ethanol and methane was compared and studied.Simulation results show that as the EGR rate increases,engine performance decreases,combustion deteriorates,NOx emissions decrease significantly,and HC and CO emissions increase.As the initial flame kernel radius increases,engine performance decreases slightly,and combustion is optimized.At low load,NOx and CO emissions decrease with increasing initial fire radius,while at high load,the results are reversed.As the equivalent ratio increase,the engine's power is enhanced,the economy is deteriorated,the peak in-cylinder pressure is increased,the peak HRR is increased,NOx emissions are reduced,HC and CO emissions are increased.As the compression ratio increase,the engine power slightly decreases,the peak in-cylinder pressure increases,the peak HRR increases,the peak in-cylinder temperature decreases,the ignition delay is shortened,the combustion duration is extended,the NO_X,CO emissions are reduced,CO₂ and HC emissions are increased.The introduction of EGR in the combustion chamber can reduce the knock intensity and delay the start time of knock.Without EGR,knocking is likely to occur on the intake side of the combustion chamber.As the EGR rate increases,the exhaust side of the combustion chamber is most prone to knocking.OH radicals can be considered as an indicator of temperature,H₂O₂ can be regarded as an indicator of the propagating flame front.OH marked the knock phase duration and HCO marked the onset of knocking.The reaction intensities of CH₂O,H₂O₂,CO and OH species were higher than other species during knocking combustion.The greater the reaction rate is,the greater the knock intensity will be.As the equivalence ratio increases,the intensity of knocking increased and the onset time occurred in advance for engines fueled with methanol,ethanol,and methane.The knocking intensity of methane is significantly weaker than that of methanol and ethanol.The knocking intensity of methanol is greater than that of ethanol.When the equivalence ratio is less than 0.9,the knocking combustion of methane disappears.