燃烧室结构与喷油策略对天然气-柴油反应活性控制压燃发动机的影响研究

Effects of Piston Bowl Geometry and Injection Strategy on Natural Gas-Diesel Reactivity Controlled Compression Ignition Engine

为优化反应活性控制压燃(reactivity controlled compression ignition,RCCI)发动机的燃烧室结构与喷油策略,基于CONVERGE数值模拟研究了挤流区高度、喉口半径与喷雾夹角对75%负荷工况下天然气—柴油RCCI发动机着火特性、燃烧特性及排放特性的影响。结果表明:增大挤流区高度可促进燃油雾化进程,有助于燃油充分燃烧,挤流区高度过大将削弱反应活性分层,降低缸内温度,增加碳烟排放量。对所研究机型而言,最优挤流区高度为6.56 mm。增大喉口半径可延长燃油喷雾进程,增加碳烟排放量,减少NO_(x)排放量,喉口半径过大会引起缸压峰值升高,NO_(x)排放量增加,对所研究机型而言,最优喉口半径为73.29 mm。随喷雾夹角的增大,燃油分布自凹坑区域上移至挤流区域,缸压峰值降低,NO_(x)排放量减少,碳烟排放量增加。

To optimize the piston bowl geometry and diesel injection strategy of reactivity controlled compression ignition(RCCI)engines,effects of the squeeze height,throat radius and spray angle on the ignition,combustion and emission characteristics of natural gas-diesel RCCI engine under 75%load condition were numerically studied by CONVERGE.Results show that the increase of the squeeze height promotes the atomization of diesel,contributing to the adequate combustion of fuels.The oversizing squeeze height weakens the reactive stratification,lowers the combustion temperature and increases soot emission.For the studied engine model,the optimal squeeze height is 6.56 mm.Increasing throat radius prolongs the diesel spray process,reduces NO_(x) emission and increases soot emission.When the throat radius is oversized,the peaks of the in-cylinder pressure and NO_(x) emission are increased.For the studied engine model,the optimal throat radius is 73.29 mm.As the spray angle increases,the distribution region of fuel moves up from the pit region to the squeeze region,resulting in the decrease of the in-cylinder pressure and NO_(x) emission,and the increase of soot emission.