湍流射流点火预燃室射流孔对甲醇发动机性能及排放影响的研究

Study of the Effects of the Pre-Chamber Nozzle on the Performance and Emissions of the Methanol Engine by Turbulent Jet Ignition

基于一台四冲程单缸发动机开展预燃室结构和射流孔直径对湍流射流点火(turbulentjetignition,TJI)甲醇发动机性能和燃烧特性的影响研究.试验采用直单孔和斜三孔两种类型预燃室射流孔,根据预燃室是否喷射甲醇,预燃室可分为主动式预燃室和被动式预燃室.结果表明,预燃室射流孔直径过大会使射流强度减弱,进而导致主燃烧室燃烧速率降低,不利于稀薄工况下的稳定燃烧;预燃室射流孔过小则会导致节流损失和淬息作用增强,造成稀薄工况缸内燃烧恶化,且污染物排放增加.稀燃工况下,对于直单孔预燃室,4 mm直单孔预燃室性能表现较好,可产生较强的射流,拓宽发动机稀燃极限、提升燃烧稳定性,同时降低指示油耗率,减少污染物排放.预燃室结构不同时,斜三孔预燃室可产生与活塞表面平行的射流火焰,TJI甲醇发动机获得更好的动力性与燃油经济性,且污染物生成较少;同时,斜三孔预燃室可在主燃烧室产生多股射流,提供分布更加广泛的点火源,促进缸内快速燃烧,有效提升稀燃工况下的燃烧稳定性.不同发动机负荷下,斜三孔预燃室的使用可使发动机获得更好的燃烧和排放性能;TJI甲醇发动机具有较好的经济性和燃烧稳定性,同时,缸内燃烧速率更高,燃烧持续期相对较短,且在稀燃小负荷工况下更为突出.

Based on a four-stroke single-cylinder engine,the effects of the pre-chamber structure and nozzle diameter on the performance and combustion characteristics of a turbulent jet ignition(TJI)methanol engine were investigated.This study used two types of pre-chamber nozzle:Straight single-hole and inclined three-hole.The pre-chamber can be divided into active and passive depending on whether methanol is injected.The results indicate that an excessively large diameter of the pre-chamber nozzle leads to a decrease in jet flame strength,which causes a reduced combustion rate in the main combustion chamber and is not conducive to stable combustion under lean conditions.Conversely,an excessively small diameter of the pre-chamber nozzle leads to throttling loss increase and quenching enhancement,resulting in the deterioration of in-cylinder combustion under lean conditions and an increase in pollutant emissions.Under lean conditions,for different diameters of the straight single-hole nozzle,the 4 mm prechamber nozzle exhibits the best performance,which produces a stronger hot jet flame.The lean limit of the TJI methanol engine is broadened,the combustion stability is improved,and both the fuel consumption rate and emission formation are reduced.For different pre-chamber nozzle structures,the inclined three-hole pre-chamber can generate a jet flame parallel to the piston surface.In this case,the power,economy,and emission characteristics of the TJI methanol engine are more optimized.Meanwhile,the multi-jet produced by the inclined three-hole pre-chamber provide more widely distributed ignition sites in the cylinder,which improve the combustion rate and combustion stability in lean conditions.The application of the inclined three-hole pre-chamber allows the TJI methanol engine to obtain better performances of the combustion and emission formation under different engine loads,and the TJI methanol engine obtains better economy and combustion stability.Meanwhile,the combustion rate in the main combustion chamber is increased,the combustion duration is shortened,and it is more prominent under lean conditions at part load.