缸内直喷氢气对发动机燃烧及排放的影响

Influence of Hydrogen Direct Injection on Engine Combustion and Emission

为探索氢发动机热效率提升及超低氮氧化物排放的技术路径,基于一台1.5 L缸内直喷氢气发动机,结合废气涡轮增压及电子增压复合技术,通过试验研究了氢气在稀薄燃烧及超稀薄燃烧模式下发动机燃烧和排放的变化规律。结果表明:在稀燃模式下,随着混合气稀释程度增大,缸内压力越来越高并前移,放热率峰值逐渐下降同时放热始点提前和放热时长变长,缸内燃烧温度下降,燃烧滞燃期和持续期逐渐变长,压升率下降;λ对NO_(x)排放的影响显著,λ=1.2时NO_(x)排放达到峰值,λ>2.5时,NO_(x)排放基本趋于0;在同样的负荷,较稀的混合气的热效率更高且NO_(x)排放更低,有效热效率达43%;全负荷时,随着λ趋向于1,扭矩逐渐升高,爆发压力和压升率也会明显上升。

In order to explore technology path of increasing the thermal efficiency of hydrogen internal combustion engine and achieving the ultra-low NO_(x)emissions,based on a 1.5 L in-cylinder direct-injection hydrogen engine,the technology of exhaust gas turbocharger and electronic boost were combined,then the combustion and emissions characteristics of hydrogen in lean-burn and ultra-lean burn conditions were studied through experiments.The results show that as the mixture concentration decreases in lean-burn mode,the in-cylinder pressure becomes higher and moves forward,the peak heat release rate gradually decreases,and the heat release start point advances and the heat release time becomes longer,and combustion temperature decreases,the ignition delay and duration of combustion gradually become longer,and the pressure rise rate decreases;the influence ofλon NO_(x)emission is obvious,whenλ=1.2,NO_(x)emission reaches its peak value,whenλis greater than 2.5,NO_(x)emission basically tends to zero;at the same load,the leaner mixture has higher thermal efficiency and lower NO_(x)emission,and the max effective thermal efficiency is 43%;at full load,asλmoves toward 1,the torque gradually increases,and the max pressure and pressure rise rate also increase significantly.