Experimental Investigation Of The Performances And Combustion Characteristics Of Methanol Engine With Turbulent Jet Ignition System

As a potential alternative fuel for internal combustion engines,methanol has the advantages of clean combustion,and it has a wide range of sources.The promotion of methanol fuel can not only alleviate the dependence of the transportation industry on petroleum resources,but also promote the efficient utilization of coal resources.Methanol has the characteristics of high-octane number,strong anti-knock ability,fast burning speed and wider ignition limit compared to traditional fuel.The widely air-fuel ratio can be obtained when the engine fueled with methanol,and the methanol engine is beneficial to apply lean-burn technology to control emissions formation and reduce fuel consumption.TJI(turbulent jet ignition)is an advanced technology that utilizes a pre-chamber to achieve lean burn.The pre-chamber jet flame entrained highly active products can provide higher ignition energy for the in-cylinder mixture and improve the burning rate and combustion stability.To investigate the characteristics of the TJI methanol engine,the experimental studies focused on the performance and combustion characteristics of the methanol engine under TJI mode were carried out based on a single-cylinder four-stroke engine bench.And a new combustion mode with high efficiency and low emissions of methanol engines was explored.First,based on the lean burn conditions,the experimental study on the performance and combustion characteristics of the TJI methanol engine was carried out,and the effect of the pre-chamber fuel injection strategy on the engine performance was studied.The results show that,compared with the SI combustion mode,the jet flame produced by the TJI mode can induce multiple ignitions in the main combustion chamber,providing higher ignition energy,resulting in a significantly shorter combustion duration in the main combustion chamber.When the methanol injection time in the prechamber is 180 °CA BTDC and the pre-chamber injection pulse is between 350-600 μs,methanol and air can be fully mixed in the pre-chamber while avoiding the excessive diffusion of methanol to the main combustion chamber.It can effectively control the air-fuel mixture concentration in the pre-chamber,and prevent the formation of the too thick or too thin mixture in the pre-chamber,thereby ensuring the jet intensity and improving the combustion performance of the engine.Under lean burn conditions,the emission of nitrogen oxides,formaldehyde and hydrocarbons in the TJI mode is more advantageous than that in the SI mode.Secondly,based on the optimal fuel injection strategy of the pre-chamber,optimization research is carried out on the diameter and structure of the pre-chamber nozzle.The results show that the excessively large nozzle hole of the pre-chamber leads to a weak jet flame,and the combustion rate in the main combustion chamber decreases,which is not conducive to stable combustion under the lean-burn condition.However,when the nozzle hole is over small,the throttling loss and quenching effect will be stronger,resulting in the deterioration of the in-cylinder combustion under the leanburn condition,and the increase of pollutant emissions.Among the single hole prechamber,the pre-chamber with the nozzle hole diameter of 4 mm shows the best performance.Further optimization of the nozzle hole structure of the pre-chamber found that the unique arrangement of holes in the inclined three-hole pre-chamber can generate a flame jet paralleled to the piston surface and reduce the heat loss caused by local overheating of the piston.The engine exhibits better power,economy and emission characteristics.Under different loads,the inclined three-hole structure prechamber still has the most balanced performance.Finally,based on the inclined three-hole pre-chamber,the optimization strategy of the TJI methanol engine under lean-burn conditions was explored.The main contributions are as follows:(1)The employ of intake boost strategy can enhance the stability of in-cylinder combustion,improve the power performance of the engine under heavy load conditions,and improve fuel economy at the same time.In addition,the intake air boost can promote the oxidation reaction of carbon monoxide,formaldehyde and hydrocarbons to reduce emissions.(2)Under the condition of small load,the method of adjusting the throttle valve is adopted to make the engine run stably under the condition of excess air coefficient λ=1.5.The TJI combustion mode can not only reduce the indicated fuel consumption rate,reduce emissions,but also improve combustion stability and avoid the deterioration of combustion leading by the over-lean mixture.(3)The improvement of the compression ratio has a little significant effect on the improvement of the engine power,but it can broaden the lean burn limit,improve the combustion stability,shorten the combustion duration and reduce pollutant emissions.