Research on Flame Propagation and Heat Transfer in Fine Fuel Particle Cloud

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Flame propagation mechanism and relating heat transfer process of fine fuel particle cloud have been investigated. At first, flame propagation phenomenon of pulverized coal cloud was observed in detail by using microgravity environment necessary to form homogeneous mixture of coal particle and air. According to the observation, two different structures of flame front, (1) continuous flame front like a flame front of gaseous mixture and (2) discrete flame front with autoignition of fuel particle ahead of flame front, are found out.The simulation of the flame propagation process with larger fuel particles was tired by using arranged foamed polystirene in line. The experimental results show that the discrete flame front appears when the particle spacing is large enough relative to the position of flame front, while the continuous flame propagation appears when the spacing is narrow. Therefore, the particle spacing is one of the most dominant factors to detrmine flame front structure. In a … More ddition to the observation of flame front structure, effects of O2 concentration, particle apacing, and particle size on flame propagation velocity were examined.According to the above experimental results the importance of heat transfer process which is determined by the relative position of unburned particle to the flame front. Especially, the case of discrete flame propagation the propagation velocity is determined by the heat transfer from the flame front to the unburned fuel. Thus, the numerical simulation on heat transfer process followed by ignition have been carried out. The results showed that the three possible mechanism on flame propagation, (1) flame propagation of gaseous mixture released from fuel particles, (2) autoignition of volatile matter close to the unburned fuel particle, and (3) surfase ignition on the fuel particle, are suggested. The range to appear the mechanism of (1) and (2) are wide and those are though to be corresponding to the flame structures observed in the pulverized coal particle cloud, respectively. Less