Characteristic time correlation for lean blowoff of bluff-body-stabilized flames

Abstract

Characteristic times associated with turbulent mixing, homogeneous chemical kinetics, liquid-droplet evaporation, and fuel injection are quantified for lean blowoff. The model linearly correlates variations in combustor pressure, inlet temperature, air velocity, flame-holder geometry, fuel type, and injector size using data obtained from three different bluff-body stabilizers that simulate the same fundamental combustion processes of both conventional and advanced prevaporizing-premixing gas-turbine combustors. The characteristic time model does not attempt to solve for the entire combustor flow field but rather considers only key regions of the flow that are important to the flame-stabilization process. Lean blowoff is viewed as the competition between a fluid mechanic and chemical time evaluated in the shear-layer region between the hot recirculation zone and the free stream. Heterogeneous effects associated with fuel evaporation and injection represent perturbations on this process that are correlated using a droplet-evaporation time and fuel-injection mixing time, respectively.