喷射参数对单喷孔CNG缸内直喷发动机混合过程的影响

Effect of Injection Parameter on Mixing Process of Single Orifice CNG Direct Injection Engine

利用数值模拟的方法,研究了喷孔直径、喷射脉宽和喷射提前角对单喷孔CNG缸内直喷的可燃混合气形成和浓混合气区域中心变化过程的影响,并利用纹影法对比了试验与仿真计算射流长度和宽度,验证了计算模型。结果表明,喷孔直径过小,浓区中心较偏向于燃烧室壁面,可燃混合气在涡旋受挤压后形成速度快;喷孔直径过大,涡旋受挤压后气体动能低,浓区中心靠近燃烧室壁面,缸内混合气形成较差;喷射脉宽增加,可燃混合气形成速度与总量增加,浓区中心靠近燃烧室壁面;当喷射脉宽过长,射流形态发生变化,影响了可燃混合气的形成;喷射提前角越小,涡旋受挤压后气体动能越大,可燃混合气生成速度越快,但可燃混合气受混合时间的影响,并且,浓区中心易受涡旋气体运动的影响;合理优化喷孔直径、喷射脉宽、喷射提前角均有利于获得均质混合气,但优化喷射脉宽和喷射提前角更有利于均质混合气的增加。

The effect of nozzle diameter,injection duration and injection advance angle on flammable mixture and dense area center of single orifice CNG engine was studied by numerical simulation.The model was verified by the comparison of the acquired length and width of jet flow between test and simulation with the schlieren method.The results showed that the small orifice led to the dense area center moving to combustion chamber wall and the rapid formation of mixture after squeezing.The large orifice led to a lower kinetic energy after squeezing that caused the poor mixing quality and made the dense area center close to chamber wall.The increase of injection duration increased the mixing velocity and flammable mixture quantity,but the dense center was still close to chamber wall.The excessively-extending injection duration would change the shape of jet flow,which influenced the formation of flammable mixture.The smaller advance angle enhanced the kinetic energy of gas after squeeziing which increased the mixing velocity.The flammable mixture amount was influenced by mixing duration and the dense area center was easily influenced by the motion of gas in the eddy.Optimizing the nozzle diameter,injection duration and injection advance angle could promote the formation of homogeneous mixture and the latter two parameters were more beneficial to improve the homogeneous mixture.