FLAME SPREAD OVER LIQUID FUELS AT GRAVITY AND MICRO-GRAVITY CONDITIONS

由于对火灾安全的重要性和对火焰传播基本机制的好奇，火焰在当前感兴趣的液体上传播的现象。为了弄清重力对火焰传播的影响，利用粒子径迹激光片法、红外热像仪和双波长全息干涉法对亚闪光和超闪光条件下的速度、温度和水蒸气浓度分布进行了实验研究。这些结果与NASA在探空火箭上进行的微重力测试进行了比较。得出以下结论：1.在亚闪蒸条件下，火焰前缘正前方的次表层液体中存在两个环流团，主要受热涡力控制，浮力次之，对次表层液体中的环流增长和温度场产生影响。循环细胞具有三维结构。寒冷的温区…更多的存在于温度低于闪点的地下液体中。冷区明显阻碍了爬行火焰向跳跃阶段的转移，因为火焰前缘没有单边积聚底层燃料蒸汽。跳跃阶段发生在冷温度谷消失后。冷区是由表面张力流和浮力驱动流相互作用形成的。红外图像显示，MUG条件下的冷区比1G条件下的要大得多。杯子内冷区的表面温度不超过闪点，使火焰在杯子条件下传播平稳，无脉动。在气相中，产生了两个再循环单元。一个形成在燃料面的水平面上，另一个形成在垂直于燃料面的垂直面上。当存在(1)向火焰传播方向移动的表面对流和(2)与火焰传播方向相反的自由气流中的气相对流时，形成这两个环流单元。再循环单元有助于使可燃层均匀。即使有像LG中浮力自然产生的萨马数量级的强迫气流，马克杯火焰也会稳定而非常缓慢地传播，其速度大约是1G的一半。由于杯子内没有液体浮力，导致液体表面的温度场有很大不同。较少

The phenomenon of flame spread over Liquid id of current interest because of its importance to fire safety and the curiosity of fundamental mechanism of the flame spread. To clarify the effects of gravity on flame spread the experimental research was excuted for measuring velocity, temperture and vapor concentration profies both in sub-flash and super-flash conditions using particle track laser sheet method, infrared thermography and dual-wave length holographic interferometry. These results were compaired with NASA's microgravity test conducted aboard a sounding rocket. Thefollowing conclusions are deduced ;1. Two circulation cells exist in the sub-surface liquid just ahead of the flame leading edge in sub-flash conditions, which are mainly controlled by the thermocopillary force, whiele the buoyancy force secondarily effects to circulation growth and chenges the temperature field in the sub-suface liquid. the circulation cells have 3-dimensional structure.2. The cold temperature zone … More exists in sub-surface liquid whose temperature is below flash point. The cold zone clearly obstruct crawing flame from shifting to jumping stage, because no substrantial fuel vapor is accumunilated ahead of flame leading edge. The jump phase occurs after the cold temperature valley disappears. The cold zone is derived by the interaction between the surface tension flow and buoyancy driven flow.3. the infrared image revealed that the cold zone in mug conditions is much larger than that of 1g conditions. The surface temperature in the cold zone in mug is not beyond the flash point, so that the flame steadily spreads with no pulsating in mug conditions.4. In gas-phase, two recirculation cells are created. One is formed in horizontal plane to the fuel surface, and the other is formed in vertical plane perpendicular to the fuel surface. Both circulation cells are formed when there is : (1) surface convection moving to the flame spread direction and (2) gas-phase convection in the free-stream air moving opposite to the flame spread direction. The recirculation cells contribute to make the flammable layr to be uniform.5. Even with forced air flow of the sama order of magnitude as that induced naturally by buoyancy in lg, the mug flame spreads steadily and very slowly, which spead is about half that of 1g. The absence of liquid-phase buoyancy in mug leads to a very differnt liquid-phase surface temperature filed. Less