WITHDRAWN: Fluid flow effects on the combustion characteristics and flame stability of methane-air mixtures in millimeter-scale burners

Abstract

This study relates to the fluid flow effects on the combustion characteristics and flame stability of methane-air mixtures in millimeter-scale burners. Numerical simulations are conducted using computational fluid dynamics to gain insights into burner performance such as temperatures, reaction rates, and flames. Fully simulations are performed that explicitly treat heat and mass transfer in the fluid as well as heat transfer in the wall. The effects of different design factors on flame stability are investigated. The effects of the velocity of fluid flow on flame stability and combustion characteristics are discussed. The factors affecting combustion characteristics are determined for cavity-stabilized burners. Particular focus is placed on determining essential factors that affect the performance of cavity-stabilized burners. The results indicate that the wall thermal conductivity and flow velocities are very important as they determine the upstream heat transfer, which is necessary for flame ignition and stability, and the material's integrity by controlling the existence of hot spots. Two modes of flame extinction occur: a spatially global type for large wall thermal conductivities and low flow velocities and blowout. There exists a narrow range of flow velocities that permit sustained combustion within a burner. For fast flows, blowout occurs, whereas for slow flows, global type extinction occurs due to slow convective heat transfer. For high inlet velocities the location of the flame shifts downstream with increasing flow rate due to the decrease in the convective timescale. For low inlet velocities, a sharp shift of the reaction zone downstream occurs with decreasing flow rate. This is due to the decrease in the heat generation rate.