Effects of inlet flow non-uniformities on thermochemical structures and quasi-one-dimensional simulation of sooting counterflow diffusion flames

Abstract

Counterflow flames are routinely used for investigating fundamental flame and fuel properties such as laminar flame speeds, autoignition temperature, extinction strain rate, and chemistries of soot formation. The primary merit of counterflow flame is that the essentially two-dimensional configuration can be mathematically treated as a one-dimensional problem with certain assumptions made; this dimensional reduction is much beneficial for computational costs, which are critical for the investigation of complex chemistries such as those of soot formation. In this work, we performed a comprehensive investigation on the performance of the 1D modeling by comparing the results with experimental measurements and the more rigorous 2D models. We focused on the effects of inlet flow uniformities, which are frequencies assumed in the 1D model but challenging to realize in experiments. Parametric studies on the effects of nozzle flow rates, nozzle separation distances, and curtain flow rates on inlet flow uniformities and the 1D modeling were performed. The results demonstrated the importance to specify actual velocity boundary conditions, either obtained from experiments or from two-dimensional modeling to the 1D model. An additional novel contribution of this work is a quantitative presentation of the fact that the presence of the curtain flow would exert a notable influence on the core counterflow by modifying the radial distribution of the nozzle exit velocity although the effects can be accounted for by using the correct velocity boundaries in the quasi-1D model. This work provides recommendation for various geometry and operational parameters of the counterflow flame to facilitate researchers to select proper burner configuration and flow conditions that are amiable for accurate 1D modeling.