Stability limits and behaviors of the diffusion flame

The flame stability limits essentially define the fundamental operation conditions of the combustion system. The critical conditions of the flame stability limits are highly dependent on flow configurations and species of fuels. For various species of fuels ( Methane, Propane and Hydrogen), the flame-base stability mechanism for flame holding has been studied. In this study, the transition behavior from the stable flame attached to the nozzle rim to lifting and blow-off is observed experimentally in the unconfined, quiescent atmosphere ([1 - 3]) The lifting and blow-off criteria are proposed for the diffusion flame. Experiments were conducted to investigate the behaviors of the spout diffusion flames for various nozzle diameters from 0.14 to 8.1 mm. The results obtained are as follows ([1]) The flame configurations and behaviors are classified in terms of the fuel nozzle diameter and fuel velocity.([2]) The blow-off velocity is increased with increasing the fuel nozzle diameter. But the lifting velocity decreases for larger nozzle diameter.([3]) As the fuel is methane and the inner diameter of the fuel nozzle is micro-scale, flame lifting and blow-off occur at the same time. No lifted flame is observed. When the fuel is propane, the flame lifts and then blows-off with increasing the spout velocity.([4]) The minimum limit of a stable flame near extinction is not dependent on the average fuel velocity, but it is dependent on the fuel flow rate.([5]) The flame length of the laminar flow regarding to the micro-scale nozzle is determined by the fuel flow rate.