Thermal and chemical structures formed in the micro burner of miniaturized hydrogen-air jet flames

The thermal and chemical structure formed in the micro burner potentially leading to the unique stability mechanism of miniaturized jet diffusion flame via excess heat recirculation through the burner wall, is studied numerically. 2-D axis-symmetric heat and mass transport processes with chemical reactions are considered in gas phase, while the heat transport process is considered in solid phase. The burner materials and fuel ejecting velocities are considered as the main numerical parameters in order to examine the role of the burner on the thermal and chemical structure inside the burner. A skeletal reaction mechanism consists of twelve steps chemical reactions and nine species is applied to consider the radical generation/consumption, and their transport in the burner. It is found that the tiny flame is stabilized even with extra-ordinary small Reynolds number, at which an extinction is generally experienced, when the low conductivity burner is adopted. This is due to the effective usage of the transferred heat from the flame to the burner to improve the stability owing to (1) preheating the incoming fuel, (2) the least heat loss from the flame toward the burner tip, and (3) enhancing the reactivity inside the burner. In such low Reynolds number jet flow with the low conductive burner, ambient air can easily diffuse back into the burner and oxidative reactions at the vicinity of the burner tip is then promoted. Accordingly, the flame structure along the axis is dramatically modified beyond the typical 1-D flame. It is suggested that the further chemical process could be promoted in the substantially-heated micro burner by considering the catalytic reaction at the inner burner surface or using oxygenated fuel likely alcohol or ether. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.