COMBUSTION IN A STRETCHED FUEL STRIP WITH FINITE RATE CHEMISTRY

This article concerns a combined analytical and numerical study of finite rate exothermic chemical reactions in a one-dimensional fuel strip embedded in an oxidizing medium. The fuel and oxidizer undergo time dependent in-plane straining motion resembling a fuel strip that is being continuously stretched by the local velocity gradients in a turbulent oxidizer field. The analytical part of the approach makes use of the Shvab-Zel'dovich formulation of species and energy equations under the assumptions of equal species mass diffusivities and unity Lewis number. Numerical solution of the fuel species equation is combined with the analytic solutions of the Shvab-Zel'dovich variables to determine the structure of the combustion field. Influence of different strain histories on fuel consumption is presented for a generic second-order chemical reaction with Arrhenius temperature dependence and unit stoichiometry. The strain histories include linearly increasing and decreasing strain rates with time and sinusoidal strain rate variations with different frequencies resembling strain rates in fluctuating flow fields. The results show significant influence of strain history on fuel consumption behavior. Straining results in considerable enhancement of combustion rates, although thermal quenching is experienced at high strain rates. Combustion behavior during low- and high-frequency oscillations in the strain rate can be quite different in that the flame does not fully respond to high-frequency oscillations. On the other hand, low-frequency oscillations can considerably enhance combustion rates.