Effects of exothermicity on unsteady diffusion flames

The effects of exothermicity on unsteady diffusion flames are analysed for one-dimensional geometries and homogeneous isobaric flow. The diffusive bur ning is described in terms of the mixture fraction by a non-linear integro- differential equation, depending on two parameters: the initial F/O ratio a nd an exothermicity factor, which is function of the heat of reaction and t he initial fuel concentration. The rates of fuel consumption with variable density increase significantly when compared to the fuel consumption rates with constant density for cylindrical and spherical flames. Their burning t imes an also significantly reduced, as a consequence of the stretching in f lame area and smaller concentration gradients. Analytical expressions are o btained for flame position, flame sheet velocity, induced flow field, compo sition, temperatures, and consumption rates. (C) 2000 Elsevier Science Ltd.