Abstract :

Activation-energy asymptotic analysis (AEA) and rate-ratio asymptotic analysis (RRA) have been employed to characterize the structure of laminar premixed flames and predict the burning velocity. In AEA the chemical reaction is presumed to take place by a one-step process, the activation energy of the one-step reaction is presumed to be large in comparison to the thermal energy. The asymptotic flame structure is presumed to be made up of a pre-heat zone that is chemically frozen and a reaction zone where chemical reactions take place. In contrast, in RRA reduced chemical-kinetic mechanisms are employed. While, the activation energy of the reactions are not presumed to be large, the Damk¨ohler number is presumed to be large. In RRA the inner-layer temperature plays a central role. It is cross-over temperature between chain-branching and chain-breaking reaction, and separates the chemically inert preheat zone from the reaction zone. It is the point of inflection in the temperature profile, and provides a kinetic criterion for flammability limits. Thus the inner layer temperature is a fundamental property of the chemical system that can be calculated from asymptotic analysis. This fundamental property is used to suggest a new procedure for predicting the laminar burning velocity from experimental measurements and computational predictions of flame structure of strained premixed flames.