Experimental study on the unique stability mechanism via miniaturization of jet diffusion flames (microflame) by utilizing preheated air system

In this work, we study the near-extinction behavior of micro-jet diffusion (i.e. non-premixed) flame, so called microflame, formed in a preheated air (up to 1020 K) in order to elucidate the unique and promising stability mechanism due to miniaturization of the jet diffusion flame. Effects of fuel flow rate and preheated air temperature on overall flame shape, flame temperature and the burner tip temperature are examined experimentally. Furthermore, the slight premixing effect on the near-extinction character is also investigated in order to support the stability mechanism suggested by this study. Methane is used as fuel and the several kinds of burner material are employed in order to examine the role of the burner. It turns out that the increasing the preheated air temperature decreases the limiting minimum flow rate effectively to simulate well the ideal condition of miniaturization of jet flame. This allows the flame to stay close to the burner and suppress the heat loss to the ambient, accordingly, the burner tip is substantially heated up. Then, the fuel flowing through the burner “receives” the heat from the burner (heated by flame) effectively to enhance the reactivity, resulting in improving the stability. It is also suggested that the endothermic radical-chain reactions are promoted near the exit of the burner when the burner temperature is substantially heated, at which the back-diffused oxygen is penetrated. Our experimental observations convince the existence of the unique and promising stability mechanism apparently found in the miniaturization of the jet diffusion flame, where the flame and burner scale are almost identical and their thermal interaction becomes prominent.