DNS study of the optimal heat release rate marker in premixed methane flames

The objective of this study is to identify a chemical marker combination that can be measured by Laser-Induced Fluorescence and used for predicting the heat release rate distribution in premixed methane-air flames at various equivalence ratios. Direct Numerical Simulations of turbulent methane flames at different equivalence ratios have been performed to obtain an indirect but accurate estimation of heat release based on all possible chemical markers. Two detailed kinetic mechanisms have been considered to check that a robust estimation is obtained. The simulation results are post-processed and analyzed by a pixel-to-pixel image comparison. At the difference of other studies, the normalized distribution of heat release and the reconstruction based on chemical markers are compared directly, so that it is possible to investigate as well geometric flame parameters, like flame thickness, for specific regions of heat release. Optimal marker combinations for measurable species have been combined with corresponding exponents. Finally, for methane flames with an equivalence ratio ranging from 0.6 to 1.4, it is found that the marker combination ([OH](1.07) x [CH2O](1.17)) (where [ ] denotes the normalized concentration) leads to a very high reconstruction quality for heat release, particularly so at high levels of heat release. Alternatively, ([H](1.11) x [CH2O](0.86)) leads to an even better approximation of the whole heat release field. However, OH-based markers are easier to measure with a good accuracy. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.