Application of large eddy simulation in methane-air explosion prediction using thickening flame approach

In this work, large eddy simulation (LES) is carried out to investigate the stoichiometric methane-air explosion through using thickening flame model. The power-law model is used to evaluate the efficiency factor and a reduced two-step combustion mechanism is considered for the methane-air combustion. The adaptive grid refinement is adopted and different thickening factors are simulated. The numerical model is validated by comparing the predicted results with experimental data. It is seen that the numerical model can reproduce the experiment data quantitatively and qualitatively. All the stages of tulip shaped flame are well repeated by LES in both 2D and 3D forms. For the flame propagating in smooth duct with tulip shaped flame formation, the effect of efficiency factor can be ignored due to its small value. The thickening factor should be estimated through using thermal thickness of premixed flame and it needs to ensure that the thickened flame can cover at least 5 grid cells. The ignition radius needs to be larger than the thickness of thickened flame to ensure the premixed flame to grow steady after the ignition.