El frente de las llamas de difusión en la zona de anclaje en el inyector y en la propagación sobre combustibles sólidos

Abstract

In this thesis we will consider two problems:1. The attachment of a diffusion ñame in the near wake of a fuel injector 2. The spreading of a diíTusion flame over a soHd fuel The purpose of this thesis is to analyze the diffusion flame front región. This región determines, in the first problem, the diffusion ñame attachment conditions. In the second problem, this región determines the flame spread velocity. These two problems share essential features even though, apparently, they are completely different.In both cases a diñ"usion flame separates the fluid field in two regions; the first región contains fuel and the concentration of oxygen is negligible; the second región contains oxygen and the fuel concentration is negligible. The diffusion flame extends from the ñame front, located near the injector, until all the fuel contained in the jet or vaporized from the solid fuel is consumed, downstream from the flame front. The diffusion flame does not reach the wall of the injector, in the first case, neither the surface of the solid fuel, in the second case, because, due to the heat losses to the solid phase, the ñame is locally extinguished. In this región, between the solid phase and the front of the fiame, there is no significant chemical reaction and premixing of fuel and oxygen takes place; as a consequence, two premixed flames -rich and lean-appear in the fiame front región. The diffusion flame starts at the point where both premixed flames merge. This structure, characteristic of the edge of a diffusion flame, is a triple ñame and it is a essential element present in both problems analyzed in this thesis.We will show that the scale of the región described above is determined by a characteristic velocity and by the balance of convection and upstream diffusion.