BURNING VELOCITIES, MARKSTEIN LENGTHS, AND FLAME QUENCHING FOR SPHERICAL METHANE-AIR FLAMES - A COMPUTATIONAL STUDY

Computations are for three modes of spherical laminar flame propagatio n: explosion, implosion, and stationary. The reduced kinetic, C-1, sch eme of Mauss and Peters is employed for a range of equivalence ratios under atmospheric conditions, with flame propagation at constant press ure. Save for the richest mixture, the scheme is fully adequate for pr esent purposes. Two burning velocities are computed, one based on the rate of disappearance of unburned gas, the other on the rate of appear ance of burned gas. These give the same laminar burning velocity when extrapolated to zero stretch rate. It is necessary to account for two different contributions to the flame stretch rate: one due to the flow field strain rate, the other to the flame curvature. These give rise to different values of Markstein length, which have been evaluated fro m the three modes of propagation. Flame quenching stretch rates are de rived from corresponding Markstein lengths and the mode of quenching i s discussed. The relevance of the results to laminar flamelet modeling of turbulent combustion also is discussed. Finally, experimental proc edures are suggested for the measurement of the stretch-free laminar b urning velocity and the different Markstein lengths.