PREMIXED TURBULENT BURNING VELOCITIES DERIVED FROM MIXING CONTROLLED REACTION MODELS WITH COLD-FRONT QUENCHING

The Eddy Breakup model has been investigated in two modified forms in which the reaction rate is quenched at the "cold front" of the flame. One quench criterion is based on the reaction progress variable (RPVQC) and the other on temperature (TQC). Burning velocities for the RPVQC have been calculated from the steady conservation equations by the use of apparently novel numerical and analytical eigenvalue techniques. Both RPVQC and TQC criteria were also studied in numerical simulations of transient one-dimensional flame propagation. The latter study also determined essential constraints on grid and time step size required to ensure accurate predictions. For the RPVQC the eigenvalue analysis and transient computations are in good agreement, provided the quench point is not close to the cold front. As quenching approaches the cold front, both analyses indicate that the reaction zone becomes infinitely thick, a behavior that is not observed in experiments on accelerating flames. These results are also consistent with the transient computations using the TQC, where good agreement was obtained for slow flame speeds in which the cold front reactant temperature is close to ambient. However, at higher flame speeds the burning velocity predicted by the TQC increased more rapidly relative to that of the RPVQC. This is because adiabatic compression raises the cold front temperature closer to that of the quench temperature. At sufficiently high flame speeds the burning velocity and flame thickness grow continuously with time ultimately leading to an unphysically propagated detonation wave. Predicting experimentally observed flame behavior with this type of modified reaction model is apparently not possible without significant cold front quenching.