Damkohler Number Analysis in Lean Blow-Out of Toroidal Jet Stirred Reactor

Abstract

Lean blowout (LBO) prediction based on the local parameters in the laboratory toroidal jet-stirred reactor (TJSR) is investigated. The reactor operated on methane is studied using three-dimensional computational fluid dynamics (CFD); the results are compared with the experimental data. Skeletal chemical kinetic mechanism with the eddy dissipation concept (EDC) model is used. Flow bifurcation in the radial (poloidal) plane due to the interaction between counter-rotating vortices creates one dominating poloidal recirculation zone (PRZ) and one weaker toroidal recirculation zone (TRZ). The Damkohler (Da) number in the reactor is the highest in the stabilization vortex; it varies from about Da ∼ 2 at ϕ = 0.55 to Da ∼ 0.2–0.3 at LBO conditions. Due to the reduced turbulent dissipation rate in PRZ, the Da number is an order of magnitude higher than in TRZ. The global blowout event is predicted at the local Da = 0.2 in PRZ. Local blowout events in the regions of low Da can lead to flame instability and to a global flame blowout at a higher fuel–air ratio than predicted by the CFD. Local Da nonuniformity can be used for optimization and analysis of combustion system stability. Further research in the process parameterization and application to the practical combustion system is needed.