Formation, growth, and transport of soot in a three-dimensional turbulent non-premixed jet flame
KAUST DepartmentClean Combustion Research Center
Physical Sciences and Engineering (PSE) Division
Mechanical Engineering Program
Reactive Flow Modeling Laboratory (RFML)
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AbstractThe formation, growth, and transport of soot is investigated via large scale numerical simulation in a three-dimensional turbulent non-premixed n-heptane/air jet flame at a jet Reynolds number of 15,000. For the first time, a detailed chemical mechanism, which includes the soot precursor naphthalene and a high-order method of moments are employed in a three-dimensional simulation of a turbulent sooting flame. The results are used to discuss the interaction of turbulence, chemistry, and the formation of soot. Compared to temperature and other species controlled by oxidation chemistry, naphthalene is found to be affected more significantly by the scalar dissipation rate. While the mixture fraction and temperature fields show fairly smooth spatial and temporal variations, the sensitivity of naphthalene to turbulent mixing causes large inhomogeneities in the precursor fields, which in turn generate even stronger intermittency in the soot fields. A strong correlation is apparent between soot number density and the concentration of naphthalene. On the contrary, while soot mass fraction is usually large where naphthalene is present, pockets of fluid with large soot mass are also frequent in regions with very low naphthalene mass fraction values. From the analysis of Lagrangian statistics, it is shown that soot nucleates and grows mainly in a layer close to the flame and spreads on the rich side of the flame due to the fluctuating mixing field, resulting in more than half of the total soot mass being located at mixture fractions larger than 0.6. Only a small fraction of soot is transported towards the flame and is completely oxidized in the vicinity of the stoichiometric surface. These results show the leading order effects of turbulent mixing in controlling the dynamics of soot in turbulent flames. Finally, given the difficulties in obtaining quantitative data in experiments of turbulent sooting flames, this simulation provides valuable data to guide the development of models for Large Eddy Simulation and Reynolds Average Navier Stokes approaches. © 2014 The Combustion Institute.
SponsorsWe acknowledge valuable support from KAUST Supercomputing Laboratory in the form of assistance with code development and computational time on the IBM System Blue Gene/P "Shaheen" at King Abdullah University of Science and Technology. The authors are also thankful for the invitation to present an early version of these results at the 2012 Summer Program held at the Center for Turbulence Research at Stanford University during the period June 24-July 20, 2012. The work at KAUST was financed in part by Saudi Aramco. M.E.M. and H.P. gratefully acknowledge the Strategic Environmental Research and Development Program (SERDP) for financial support through Grant No. WP-2151 with Dr. Robin Nissan as the program manager.
JournalCombustion and Flame