直喷式柴油机火焰浮起不对称性的数值模拟

摘要

To reasonably evaluate the turbulent diffusion flame lift-off asymmetry in DI diesel engines,an evalua-tion system was established. This evaluation system consists of a coordinate system,a measurement criterion and definitions of some characteristic parameters. The turbulent diffusion flame lift-off asymmetry and some related prob-lems in a DI diesel engine were studied with this evaluation system. After the model’s validity was proved,the devel-opments of the flame lift-off asymmetry characteristic parameters along with time scale,surface proximation and swirl speed were respectively investigated. The results indicatethat the fuel sprays’ proximation to the wall and the swirl rotational speed are the key factors inducing flame lift-off asymmetry in DI engines,which lays foundationfor effective control of flame lift-off length and decrease of soot emission.%为了合理评价直喷式柴油机湍流扩散燃烧火焰浮起的不对称性，建立了一个新的评价体系。该评价体系包括一个评价平面系、度量标准以及若干特征参数的定义，并在该评价体系内以数值模拟的方式研究了直喷式柴油机湍流扩散燃烧火焰浮起不对称性的相关问题。在所建 CFD 三维数值分析模型的有效性得到相关试验数据的验证后，采用验证后的模型分别研究了火焰浮起不对称性的各表征参数随时间发展、贴壁程度和涡流转速的变化趋势。分析结果表明，喷油油束的贴壁程度以及缸内的涡流转速是产生火焰浮起不对称性的主要原因。该研究为采取有效措施调控火焰浮起长度、降低柴油机碳烟排放奠定了基础。