喷射器位置对天然气发动机燃烧特性的影响

Influence of Injector Position on Combustion Characteristics for Natural Gas Engine

以高压直喷天然气发动机为研究对象,借助计算流体仿真软件CONVERGE探究高负荷下喷射器布置对缸内燃烧及排放特性的影响。每种燃料(柴油和天然气)分别通过2个独立喷射器实现缸内高压直喷,设计了中心对称和左右对称两种布局方式,并基于每种布置开展喷射器距离对发动机性能的影响研究。结果表明:喷射器距离影响柴油火核与射流区的相对位置,进而影响对天然气的引燃效果。两种布置方案下燃料分布差异大,随着喷射器距离增大,左右对称布置下富燃现象得到改善,中心对称布置下更多燃料分布在近壁处,火焰传播速度减慢;采用中心对称布置,燃烧持续期缩短,指示平均有效压力和缸内峰值压力提高,燃烧重心CA50提前,soot排放减少而NOx排放增加。

The numerical investigation based on the CFD code CONVERGE was carried out to explore the influence of injector placement on combustion and emission characteristics of a dual fuel engine with two high pressure direct injectors for each fuel(diesel and natural gas)under heavy-load condition.Two separate layouts,respectively named bilateral symmetry and centrosymmetry,were considered in the paper and a thorough sensitivity study was carried out with positioning of the fuel injectors as a variable.The results show that the distance between dual fuel injectors affects the relative position between diesel auto-ignition flame kernel and natural gas jet,and it will further lead to different combustion quality of natural gas subsequently pilot-ignited with diesel.There is a great difference in fuel distribution between the two layouts.With the distance between injectors increases,the challenge of fuelrich combustion is mitigated for bilateral symmetry mode,while more fuels close to the cylinder wall and lower flame propagation are obtained for centrosymmetry mode.With centrosymmetry arrangements,shorter combustion duration,advanced combustion phase,higher IMEP,higher in-cylinder pressure peak and higher emitted NOx are achieved,and the soot emission reduces.