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

液体表面的火焰传播现象是当前人们研究的热点，因为它对火灾安全具有重要意义，而且人们对火焰传播的基本机理还很好奇。为了研究重力对火焰传播的影响，采用激光片光法、红外热像法和双波长全息干涉法对亚闪和超闪条件下火焰传播的速度、温度和蒸汽浓度进行了测量。这些结果与美国宇航局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.在亚闪焰条件下，火焰前缘前的亚表面液体中存在两个环流胞，它们主要受热偶力的控制，而浮力的作用对环流的增长起次要作用，并改变了亚表面液体中的温度场。循环单元具有三维结构。冷温区 ...更多信息 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，因为在火焰前缘前没有实质性的燃料蒸气被蒸发。跃变阶段发生在低温谷消失之后。冷区是由表面张力流和浮力驱动流之间的相互作用产生的.红外图像显示，在马克杯条件下的冷区比1G条件下的冷区大得多。保温杯内冷区表面温度不超过闪点，使火焰在保温杯内稳定传播，无脉动.在气相中，产生两个再循环单元。一个形成在相对于燃料表面的水平面中，另一个形成在垂直于燃料表面的竖直平面中。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移动的自由流空气中的气相对流时，形成两个循环单元。再循环单元有助于使可燃层均匀.即使强制空气流的数量级与lg中自然浮力引起的数量级相同，杯状火焰的传播稳定且非常缓慢，其传播速度约为1g的一半。由于马克杯中液相浮力的缺乏，导致其液相表面温度场有很大差异。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