Modeling of Turbulent Combustion Process and Lean Blowout of Diffusion and Premixed Flames Using a Combined Approach

Most of the modern combustor’s designs use staged concepts for reducing thermal NO emissions. Usually, a combustion process takes place inside the main zone, which uses very lean premixed fuel/air mixtures. A diffusion pilot zone supports combustion process inside a lean main zone. Thermal NO formation process takes place predominantly inside hot diffusion flame. So, operation modes of pilot and main zones must be arranged to provide low NO emissions of pilot zone and maintain flame stability inside the main zone simultaneously. In this paper, a new turbulent combustion model is presented. This model allows to model diffusion and premixed flames and takes into account various physical processes, which lead to flame destabilization. The model uses an equation for reaction progress variable. Within the considered approach this equation has two source terms. These terms are responsible for different conditions of combustion process: diffusion flames and premixed flames, and distributed reacting zones. This paper studies the problem, concerning modeling of lean blowout process of diffusion flame front. To test the proposed combustion model we have simulated lean blowout process inside combustion zone of a gas turbine combustor. Good predictions of lean blowout limits were obtained.