Flame behavior inside constant diameter cylindrical meso­scale combustor with different backward facing step size

Abstract

This research observes the behavior of the flame stability in a cylindrical meso-scale combustor at various backward facing step sizes. The backward facing step was varied by changing the size of the combustor inlet diameter while the size of the combustor outlet diameter was kept constant, keeping a constant contact area. Butane gas (C4H10) was used as fuel with air as the oxidizing agent. The results show that generally, the flame mode and area of the flame mode map are obtained for the conditions of the stable flame at combustor rim, stable flame in combustor, stable flame near the step, oscillating flame, oscillating spinning flame, spinning flame, flashback, and no ignition. Flame mode and flame mode map distribution depend on reactant flow velocity behavior, jet flow generating shear stress, vortex flow regulating wall-thermal interaction, and average flow generated by varying the backward facing step size at various equivalence ratio and reactant velocity in the test range. Jet flow destructs flame stability to be extinct due to strong shear stress. Vortex flow spins the flame while the transition from jet to vortex flow oscillates the spinning flame. Weak vortex at average flow plays an important role in wall-thermal interaction that keeps flame very stable. Decreasing the backward facing step size tends to widen the flame stability region, but the combustion process causes the flame to be flashed back. By setting the reactant velocity at a small backward facing step size to the condition where the weak vortex flow exists, flashback conditions could be avoided keeping the flame very stable. Stable flame tends to be performed around stoichiometric to the lean mixture and in the low to medium reactant flow velocity. At high reactant flow velocities, the flames tend to be unstable. However, at low to medium reactant flow velocity, the flame tends to be stable in the combustor