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

研究了细燃料颗粒云的火焰传播机理及相关的换热过程。首先，利用煤粉与空气形成均匀混合物所需的微重力环境，详细观察了煤粉云的火焰传播现象。根据观测结果，发现了两种不同的火焰前锋结构：(1)连续的、类似气体混合物火焰前锋的火焰前锋；(2)火焰前锋前方燃料颗粒自燃的离散火焰前锋。实验结果表明，当颗粒间距相对于火焰锋面位置足够大时，会出现离散火焰锋面，而当颗粒间距较小时，会出现连续火焰传播。因此，颗粒间距是决定火焰锋面结构的最主要因素之一。在…中在观察火焰锋面结构的基础上，考察了氧气浓度、颗粒间距和颗粒尺寸对火焰传播速度的影响。根据以上实验结果，由未燃烧颗粒与火焰锋面的相对位置决定了传热过程的重要性。特别是，在离散火焰传播的情况下，传播速度取决于从火焰前沿到未燃烧燃料的换热。为此，对点火后的换热过程进行了数值模拟。结果表明，火焰传播的三种可能机制是：(1)燃料颗粒释放出的混合气体的火焰传播；(2)靠近未燃烧燃料颗粒的挥发分的自燃；(3)燃料颗粒表面的点火。(1)和(2)机理出现的范围较宽，分别与观察到的煤粉云中的火焰结构相对应。较少

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