Study On Cold Start And Transient Response Performance Of Methanol Engine

Compared with fossil fuels,methanol has high oxygen content and full combustion,so it is an ideal alternative fuel for petroleum.However,methanol has a high latent heat of vaporization,low calorific value and is a single component fuel.When it is used in internal combustion engines,the mixture quality will be poor due to the poor vaporization of methanol,resulting in difficulties in cold start and poor response to acceleration conditions.In order to improve the cold start performance and acceleration performance of methanol machine,three aspects of research work are carried out in this paper.In order to improve the cold start performance of the methanol engine,a scheme was proposed to heat a small amount of methanol to form a mixture and use the heat generated by the mixture combustion to vaporize the amount of methanol needed by the internal combustion engine.The multistage heater was designed based on the demand of driving and idle conditions,and the structural parameters of the multistage heater were simulated and analyzed by CFD simulation technology.The results show that the depth of the methanol intake pipe into the inlet pipe of the heater,the Angle of the expansion section of the heater,whether the porous medium is used and the Angle of the contraction section of the heater affect the performance of the multistage heater.After the use of porous media,the mass fraction of methanol in the mixture at the outlet of the heater increased from 53%to 71%.The multistage heater control system is developed,the experimental bench of multistage heater is built,and the performance of multistage heater is verified by simulation experiment.The results show that the air-fuel ratio of methanol-air mixture around spark plug can be adjusted by adjusting the heating power.When the mixture around the spark plug is the ideal air-fuel ratio,the ignition success rate of methanol is the highest,and the ignition success rate decreases as the air-fuel ratio deviates from the ideal air-fuel ratio.As the ambient temperature drops,the heat transfer of methanol vapor to the multistage heater housing increases,resulting in lower mixture temperature,and part of methanol vapor may turn back to liquid state,resulting in lower mixture concentration around the spark plug.When the ambient temperature is lower than-12℃,the ignition success rate corresponding to the ideal air-fuel ratio is also lower than 100%.When the ambient temperature drops to-21℃,the ignition success rate will be less than 70%.In the case of successful ignition,the ambient temperature is-21℃,and the methanol temperature at the outlet of the heater is still higher than the methanol evaporation temperature.Under the acceleration condition of multi-point injection methanol machine,the airway surface can not provide enough heating power,resulting in poor response of methanol machine in acceleration condition.This paper designs a methanol preheating system with high temperature circulating water as the heat source,and uses high temperature circulating water as the heat source to increase the temperature before methanol injection.The experimental results show that when the heat source of the preheater increases from 70℃ to 100℃,the amount of methanol that can be evaporated directly after injection increases from 1.36%to 4.21%,and the remaining methanol liquid is at a temperature of about 64.5℃.The design of preheater is completed.When the combustion mode of methanol-diesel dual fuel internal combustion engine is switched,the rotation speed fluctuation will occur due to the improper matching between increasing methanol injection and decreasing diesel injection.In this paper,it is proposed that methanol is injected into the EGR pipeline,and methanol is directly endothermic vaporized from the high temperature exhaust gas and uniformly enters each cylinder with the circulating exhaust gas.An external methanol evaporation system ECU based on tail gas heating was developed,and the prototype transformation and experimental bench construction were completed.The time between methanol injection and evaporation entering the combustor to participate in combustion was examined under different EGR valve opening.The results show that the time from methanol injection to methanol vapor entering the cylinder is related to methanol injection amount,engine operating condition and EGR valve opening.With the same amount of methanol injected,increasing the EGR valve opening reduces the time for methanol to evaporate and enter the cylinder.In practice,based on the time from methanol injection to its participation in combustion,controlling the time to reduce the injection amount of diesel fuel can reduce the rotational speed fluctuation during combustion mode switching.