Limitations of simplified models to predict soot formation in laminar flames
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(2020) 42:340
TECHNICAL PAPER
Limitations of simplified models to predict soot formation in laminar flames L. Zimmer1,2 · F. Pereira1 Received: 23 October 2019 / Accepted: 13 May 2020 © The Brazilian Society of Mechanical Sciences and Engineering 2020
Abstract Soot formation and radiation are important aspects for combustion problems. In this work, numerical simulations of ethylene coflow laminar flames are used to evaluate soot formation and radiation processes under different modeling approximations. Priority was given for models that were capable of producing detailed information with reduced computational requirements. So, the objective of this work is to show and quantify the importance of heat loss by gas and soot radiation and to quantitatively show the impact of different transport models (a detailed and a simplified) in soot predictions. For soot modeling, a semiempirical two-equation model is chosen for predicting soot mass fraction and number density. The model describes particle nucleation, surface growth and oxidation. For flame radiation, the radiant heat losses (gas and soot) are modeled by using the gray-gas approximation with optically thin approximation. For the chemical kinetics, a detailed approach is employed. It is found that gas and soot components of the radiative heat loss are comparable, with the gas radiation being larger (65%). To capture 99.9% of the total heat loss, the numerical domain has to be extended to 2.4 times the flame length based on the stoichiometric mixture fraction. Radiation modeling has a large impact on soot predictions. An error of 19% in the peak soot volume fraction is found when radiation is neglected. Errors due to simplified transport properties are also around 21%. Keywords Diffusion flame · Soot modeling · Radiation
1 Introduction Combustion is still the most important energy conversion process in the world. Nevertheless, combustion is responsible for the major part of human emissions of gaseous pollutants and particulate matter to the atmosphere, resulting in negative impacts to the environment and health of humans and animals [1–4]. Thus, many research and development efforts are driven by the increasing need to enhance the efficiency of combustion processes and to reduce pollutant Technical Editor: Mario Eduardo Santos Martins, Ph.D. * L. Zimmer [email protected] 1
Mechanical Engineering Department, Federal University of Rio Grande do Sul, Rua Sarmento Leite, n. 425, Porto Alegre, Brazil
Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria St., Toronto, ON M5B 2K3, Canada
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emissions. In order to achieve these goals, a fundamental understanding of the major phenomena of combustion processes is required. In this scenario, modeling tools that are able to predict the main characteristics of flames with low computational cost are of great interest for the industrial and the scientific communities. Addressing all the phenomena combustion processes can be a major challenge for numerical simulations. For
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