Experimental Study On Cold Engine Ignition Performance Of Methanol Engine Based On A Heated Pre-chamber

Methanol is an ideal alternative fuel for fossil energy,but due to its high boiling point,high latent heat of vaporization,and low vapor pressure,methanol engines have serious problem of cold starting.Turbulent jet ignition(TJI)in the pre-chamber is a high-energy ignition method,which can increase the flame propagation speed and improve the combustion stability and thermal efficiency of the engine.The methanol jet ignition engine needs further research and development,and it also has the problem of difficult cold start.Therefore,this paper independently developed a heated prechamber turbulent jet ignition device,and carried out in-depth experimental research on the cold engine ignition performance of methanol TJI engine.First,based on the visual constant volume incendiary bomb,the combustion characteristics tests of SI and TJI under different boundary conditions were carried out,and the effect of pre-chamber heating on jet ignition characteristics under low temperature and lean conditions was investigated.The results show that,compared with the SI ignition method,the TJI jet ignition directly develops into turbulent combustion without going through the laminar combustion stage,which can significantly accelerate the methanol flame.Under different excess air coefficients,the following phenomena appear: when the temperature of the constant volume incendiary bomb is only 50 ℃,the methanol vapor introduced will condense,so that the methanol SI flame burns the fastest when the theoretical excess air coefficient is 0.6,when the excess air coefficient is 1.0,the flame burning speed of the passive TJI is the fastest;the use of the prechamber heating device does not expand the lean limit of the passive TJI,but only slightly increases the jet flame speed;for the active TJI,the heating The combustion chamber can significantly improve the flame burning speed of the hot jet,and the active pre-chamber heated to 130 °C produces an obvious jet flame when the excess air coefficient is 2.2,which shows that the condensation problem in the pre-chamber is improved.Secondly,the experimental study of methanol TJI engine under different boundary conditions is carried out.The results show that the high-speed jet flame in the prechamber accelerates the in-cylinder combustion process,significantly shortens the combustion duration,and advances the combustion phase under cold idle conditions.The igniting test of the cold engine was carried out under different cooling water temperature conditions,and it was found that under the cold boundary condition,the fuel in the pre-chamber was difficult to evaporate,and the phenomenon of condensation attached to the wall was serious,which led to the difficulty of ignition of the methanol TJI engine when the cooling water temperature was 25 ℃ and below.At the same time,due to the difficulty in discharging the exhaust gas in the pre-chamber,the IMEP oscillation phenomenon occurs repeatedly in the misfire-ignition-misfire cycle.Secondly,in view of the phenomenon of fuel condensing on the wall of the active pre-chamber under the cold boundary condition,the external heating strategy was adopted for the pre-chamber at the ambient temperature of 25 ℃ and 0 ℃.It is found that the pre-chamber heating can significantly reduce the misfire cycle,advance the time of successful ignition cycle and stable combustion,and improve the ignition performance of the engine.When the pre-chamber is heated to 70 ℃,the ignition performance of the engine is close to that of heating the cooling water to 50 ℃.The ignition performance of the engine;at the same time,the pre-chamber heating strategy does not produce excessive CO and HC emissions compared with the enriched start strategy;the heated pre-chamber can advance the combustion phase at the initial stage of ignition without affecting the combustion duration.Finally,the effects of pre-chamber parameters on the cold ignition performance of methanol TJI engine were studied.Pre-chamber parameters included pre-chamber diameter and pore structure,pre-chamber injection timing,and pre-chamber fuel injection volume.The study found that the IMEP oscillation phenomenon will be more serious when the straight hole 2 mm pre-chamber is used;the ignition performance of the engine is the best when the straight hole 6 mm pre-chamber is used,which is due to the large cross-sectional area of the jet hole,the exhaust gas can be effectively discharged as the piston goes down and generate a stable jet flame;in the cold engine state of 25 ℃,the injection timing of the pre-chamber has little effect on the ignition performance,and increasing the fuel injection volume of the pre-chamber can obviously make successful ignition cycle appears earlier.