Stabilization of the sub-limit lean premixed flame by concentrated-microwave burner

By affecting the ion motions and electron temperature in the flame, microwave is shown to effectively enhance and stabilize the flame in the sub-limit lean premixed region. In this research, we first develop and set up the microwave jet combustor system for fundamental studies of the stabilization mechanism of the sub-lean limit flames. The control parameters and operation characteristics of the integrated system is further investigated. The microwave energy is enhanced and applied to the combustion system by means of a rectangular resonant cavity. In order to concentrate the microwave energy and enhance the absorption of microwave energy by the flame, a novel design of microwave centralized burner is used to incorporate microwave (2.45GHz) electromagnetic energy directly into the reaction zone of a premixed laminar methane-air flame for flame enhancement. Depending upon the input microwave power, three enhanced stages (1) Electric Field Enhanced (2) Transition and (3) Full Plasma Assisted can be categorized. Results show that with the onset of a plasma flame by microwave, a significant rise in both excited state species, CH and OH radical emission intensity was observed and the addition of microwave has been shown to broaden the lean flammability limit to equivalence ratio=0.38, far below the lean flammability limit of the methane flame.