Abstract:

In order to investigate the combined burning characteristics of soaked porous media sand bed under different combustible liquid layer heights, a series of burning tests with different sand sizes and liquid layer heights were conducted. The characteristic parameters, fuel (ethanol) mass loss rate, flame height, internal temperature of porous media (quartz sand) and plume temperature were measured, and the effect mechanism of liquid layer height was analyzed and studied. The results show that the existence of combustible liquid layer has a certain effect on burning characteristics of quartz sand infiltration layer. When there is a liquid layer above the sand layer (h=20—60 mm), the mass loss rate of quartz sand infiltration layer increases obviously, which can be attributed to the preheating effect of liquid layer burning. The flame height increases firstly and then stabilizes with the increase of liquid layer height, which shows the similar trend with mass loss rate. The temperature growth retardation occurs inside sand bed within 78.7—79.0℃ (which is close to fuel boiling point), so the vapor zone movement speed inside sand bed can be evaluated. As the height of the liquid layer increases and the particle size of the quartz sand decreases, the velocity of the vapor zone in the sand layer gradually increases. In addition, based on previous scholar's plume relationship and current experimental data, an empirical formula is obtained to describe axial temperature of flame and plume for combustible liquid-soaked inert porous media sand bed.

Key words: porous media, liquid layer height, combustion, phase change, heat transfer, flame appearance

摘要：

为探究不同可燃液体层高度下浸润多孔介质砂床组合燃烧特性，开展了一系列不同粒径和液体层高度的燃烧测试，测量了燃料（乙醇）质量损失速率、火焰高度、多孔介质砂床（石英砂）温度和羽流温度等特征参数，分析研究了液体层高度的影响机制。结果表明：可燃液体层的存在对浸润石英砂层燃烧特性具有一定的影响。当砂层上方存在液体层时（h=20~60 mm），浸润石英砂层燃料质量损失速率明显增大，这可归因于液体层燃烧的预热作用。火焰高度随液体层高度增加而先增加随后几乎不变，表现为与质量损失速率相似趋势。浸润石英砂层内部在78.7~79.0℃（接近燃料沸点）出现温度增长迟滞，据此可对砂层内部蒸气区移动速率进行评估。随着液体层高度增加及石英砂粒径减小，砂层内蒸气区移动速率逐渐增大。此外，基于前人推荐的羽流关系和当前实验数据，获得了描述可燃液体浸润多孔介质砂床燃烧火焰羽流轴向温度经验公式。

关键词: 多孔介质, 液体层高度, 燃烧, 相变, 传热, 火焰特征