DYNAMICS AND STRUCTURE OF INTERACTING NONPREMIXED FLAMES

Interaction between neighboring parallel and nearly parallel flames oc curs more frequently as the turbulent length scales become smaller, an d when a flame trapped in a large vortical structure spins further ins ide its core. In this paper, a model to simulate the interaction betwe en neighboring, strained thin flames is proposed, and is used to inves tigate the mechanism and impact of the interaction for the case of a m ethane-air flame described by a four-step reduced kinetics mechanism. In the model, the interaction between neighboring strained flames is s implified by combining them into a single stagnation-point flow struct ure with one of the major reactants trapped in the vicinity of the sta gnation plane. We find that in both cases of flames converging toward the oxidizer or the fuel, the interaction does not occur until the rea ction zones overlap. The difference between the two cases is caused by the deep penetration of oxygen into the fuel side in the former case as opposed to the rapid decomposition of the fuel as soon as the tempe rature rise is sufficiently high in the latter case. In both configura tions, during the interaction phase, the burning rate increases as the hydrogen radical concentration rises due to the overlap of the two re action zones, leading to a sudden termination of combustion as the tra pped reactant is depleted, followed by an overshoot in the peak temper ature. Thus, the interaction between neighboring flames is governed by chemical rather than thermal exchange. The burning enhancement in the first case is connected with the abundance of H in the last stages of oxygen consumption, while in the second case, it is due more to the b urning of CO. Results also show that the after-extinction evolution of CO is quite different in two the cases. In the case of flames interac ting across the oxidizer, the after-extinction dynamics of CO is simil ar to that of other major species, while for flames converging toward the fuel, CO after reaching levels higher than encountered in isolated flames, is rapidly consumed. (C) 1998 by The Combustion Institute.