Experimental Study On Cold Start Performance And Combustion Characteristics Of Spark Ignition M100 Methanol Engine

With the rapid development of social economy,the consumption of oil resources is huge.Considering the energy security and energy diversification,it is imperative to explore and apply alternative fuels.As one of the most potential alternative fuels,the application of methanol in internal combustion engine has always been concerned by the industry.However,due to the large latent heat of methanol vaporization and low evaporation rate during cold start,it is difficult to start methanol.Therefore,it is of great significance to study the cold start of SI Methanol Engine in this paper.The compressed air-assisted injection technology can achieve high atomization quality of fuel with lower fuel supply pressure,and spray SMD(Sauter mean diameter)can reach less than 10μm.From this point of view,a single cylinder gasoline engine is equipped with a self-developed inlet air assisted injection system(AAPI).In order to make full use of the high atomization effect of AAPI technology on methanol,the double injection strategy was applied to optimize the cold start performance of methanol engine.The effects of the advanced injection timing,the advanced methanol injection duration,the open valve injection timing and the ratio of two methanol injection on the cold start performance and the first cycle combustion characteristics of the ignition methanol engine were investigated experimentally.The experimental results show that the improvement of methanol atomization quality can effectively improve the quality of combustible mixture preparation under cold start condition,and the double injection strategy based on AAPI technology is an effective method to improve the cold start performance.The second stage methanol injection using open valve injection can make better use of the intake roll to promote the spray evaporation of methanol.The mixing of 30～40°CA before the crankshaft angle at the highest inlet velocity is more conducive to improving the combustion characteristics of the first ignition cycle.The injection time of the first stage should be kept at 250°CA before the second stage.At this time,extending the evaporation time is the main factor to promote methanol evaporation.In the second injection strategy,a large proportion of methanol should be injected into the airway in the form of second stage valve opening injection,which can greatly improve the maximum combustion pressure and cold start performance of the first cycle.Under the condition of fixed mixture injection duration,the increase of injection pulse duration will lead to the decrease of spray quality.The experiment shows that with the increase of the first injection duration,the cold start performance and the first ignition cycle combustion characteristic all decrease,so improving the atomization quality of methanol is more effective than increasing the methanol injection rate to improve the cold start performance.Under the condition of mixture injection duration,the increase of injection pulse duration will lead to the decrease of spray quality.The experiment shows that with the increase of the first injection pulse duration,the cold start performance and the first cycle combustion characteristic all decreased,so improving the atomization quality of methanol is more effective than increasing the methanol quantity to improve the cold start performance.The SMD of air-assisted methanol atomization is 5-10 times smaller than that of direct atomization.By comparing the effects of the two atomization methods on the cold start performance,it is found that the methanol injection with high atomization quality can effectively improve the cold start performance and improve the work ability under the cold start condition.Ambient temperature and ignition timing have great influence on the cold start performance of SI methanol engine.The experiment results show that the corresponding cold start time is 0.81 s,1.2s,2.1s,5.5s and 10.5s when the ambient temperature is 25℃,18℃,15℃,11℃ and 5℃,respectively.With the decrease of temperature,the starting speed fluctuates obviously,and the reliability and stability of cold start decrease.Under cold start condition,the ignition timing at 20-25°CA BTDC contribute strongest combustion quality and the shortest ignition delay,which can effectively shorten the cold start time and speed stability.Based on AAPI,the effects of different ignition timing,excess air coefficient λand injection start time on combustion characteristics were analyzed by steady speed bench experiments.The results show that when the ignition advance angle is 30 °CA BTDC,the cycle variation of the peak combustion pressure is small,the combustion is relatively delayed,the ignition angle is more stable,and the IMEP is the largest at this time.The methanol mixture concentration under warm-up condition is relatively diluted than that under cold start-up condition.The combustion stability is higher in the range of λ=0.75～0.8,and the average IMEP is larger,which is conducive to the dynamic performance under warm-up condition.Under the warm-up condition,methanol is injected when the intake valve is opened,and the methanol evaporation is greatly affected by the inlet air flow,which is conducive to the uniformity of the mixture in the cylinder.