A Non-Monotonic Blow-off Limit of Micro-Jet Methane Diffusion Flame at Different Tube-Wall Thicknesses

In order to provide guideline for choosing a suitable tube-wall thickness (δ) for the micro-jet methane diffusion flame, the effect of tube-wall thickness on the blow-off limit is investigated via numerical simulation in the present work. The results show that the blow-off limit of micro-jet methane diffusion flame firstly increases and then decreases with the increase of tube-wall thickness. Subsequently, the underlying mechanisms responsible for the above non-monotonic blow-off limit are discussed in terms of the flow filed, strain effect and conjugate heat exchange. The analysis indicates that the flow field is insignificant for the non-monotonic blow-off limit. A smaller strain effect can induce the increase of the blow-off limit from δ=0.1 to 0.2 mm, and a worse heat recirculation effect can induce the decrease of the blow-off limit from δ=0.2 to 0.4 mm. The non-monotonic blow-off limit is mainly determined by the heat loss of flame to the tube-wall and the performance of tube-wall on preheating unburned fuel. The smallest heat loss of flame to the tube-wall and the best performance of tube-wall on preheating unburned fuel result in the largest blow-off limit at δ=0.2 mm. Therefore, a moderate tube-wall thickness is more suitable to manufacture the micro-jet burner.