期刊
COMBUSTION AND FLAME
卷 219, 期 -, 页码 70-85出版社
ELSEVIER SCIENCE INC
DOI: 10.1016/j.combustflame.2020.04.019
关键词
Soot modeling; Oxygen enrichment; Oxy-combustion; Strained flames; Counterflow flame
类别
资金
- Washington University in St. Louis
- U.S. Department of Energy [DE-PI0000017]
Due to the size and complexity of industrial-scale systems and computing limitations, semi-empirical soot models are often employed in CFD simulations rather than computationally-expensive detailed mod-els. Many of these models were developed for specific applications with unique characteristic timescales and/or validated only under fuel-air combustion conditions. Hence, their use in different contexts, such as oxy-combustion, could lead to inaccurate predictions. In this study, twelve semi-empirical models (1-step or 2-step) are evaluated on their ability to respond to changes in stoichiometric mixture fraction (Z(st)) and strain in a series of ethylene counterflow flames which span the experimental sooting-to-non-sooting (yellow to blue) transition. A unique approach of plotting soot formation rate in normalized, local equivalence ratio space is introduced to aid in the analysis. Results show that no existing model is able to predict a blue flame when Z(st) is increased beyond the experimentally-measured sooting limit. Many models give the counter-intuitive result of increasing peak and/or integrated soot volume fraction (svf) as Z(st) increased, contrary to experimental observations. Two models are able to successfully predict a blue flame upon increase of strain to the sooting limit value. For two-step models, the strong dependence of growth rate on surface area results in high sensitivity of svf to changing flame boundary conditions, but with mixed accuracy. There remains a significant need for a robust semi-empirical model which can accurately predict soot fraction in systems with oxygen-enrichment or variable strain. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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