Laminar burning velocity measurements of refrigerants under terrestrial and microgravity conditions

陆地和微重力条件下冰箱的层流燃烧速度测量

• 批准号: 520589628
• 负责人: Dr.-Ing. Joachim Beeckmann
• 金额: --
• 依托单位: Institut für Technische Verbrennung (ITV)
• 依托单位国家: 德国
• 项目类别: Research Units
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/520589628?language=en
• 关键词: Laminar; burning; velocity; measurements; refrigerants

Next-generation refrigerants with lower global warming potential for cooling and heating applications pose increased fire hazards due to their high flammability. Classification of a substance’s fire hazard potential includes not only flammability but also the evaluation of its laminar burning velocity, a quantity additionally representing reactivity and exothermicity. Conventional methods for determining laminar burning velocities measure a mixture's flame propagation speed, for instance, by assessing spherical flames. Due to the slow propagation speed of most refrigerant flames, the impact of two physical phenomena significantly increases: (1) The buoyancy-induced deformation of the flames, and (2) the radiation heat losses, invalidating the underlying assumptions required for experimental methods. Hence, standard data extraction assumptions, such as spherical flame shape, fail and accurate literature data on flame velocities for these refrigerants are rare. To obtain a fundamental understanding of the refrigerant’s combustion behavior and to provide accurate flame velocity data, the flame structure, propagation, and surrounding gas dynamics must be studied in detail using high-fidelity experiments. In this project, robust methods will be developed to reliably characterize the combustion behavior of refrigerants. First, the buoyancy deformation effects of slow-propagating refrigerants will be investigated using Particle Image Velocimetry (PIV). The flame front's local curvature and strain effects are key factors in determining burning velocities. Microgravity experiments, conducted in the drop tower facility of the Center of Applied Space Technology and Microgravity (ZARM) of the University of Bremen, will provide buoyancy-free flame propagation data, isolating the radiation heat loss effect. These heat losses will be quantified by the spatially and temporally resolved flame temperature fields obtained using the high-speed Rayleigh scattering. The findings will help develop and modify existing radiation correction models, that were developed for hydrocarbons but have not yet been validated for refrigerant flames. Finally, a flame structure analysis based on an asymptotic approach with a multi-step reaction scheme will be performed to reveal the underlying physicochemical processes involved in the ignition, extinction, and propagation of refrigerant/oxidant mixtures. The applicability of the existing asymptotic approaches will be studied, and modifications tailored explicitly for refrigerant flames will be applied. This will contribute to developing an accurate and robust simplified modeling approach with approximation formulas for the burning velocities of refrigerant flames.

用于冷却和加热应用的全球变暖潜能值较低的下一代制冷剂由于其高可燃性而增加了火灾危险。物质潜在火灾危险的分类不仅包括可燃性，还包括对其层流燃烧速度的评估，该速度还代表反应性和放热性。用于确定层流燃烧速度的传统方法例如通过评估球形火焰来测量混合物的火焰传播速度。由于大多数制冷剂火焰的传播速度缓慢，两种物理现象的影响显着增加：（1）浮力引起的火焰变形，以及（2）辐射热损失，从而使实验方法所需的基本假设无效。因此，标准数据提取假设（例如球形火焰形状）、失败以及有关这些制冷剂火焰速度的准确文献数据很少。为了从根本上了解制冷剂的燃烧行为并提供准确的火焰速度数据，必须使用高保真实验详细研究火焰结构、传播和周围气体动力学。在该项目中，将开发可靠的方法来可靠地表征制冷剂的燃烧行为。首先，将使用粒子图像测速（PIV）研究缓慢传播制冷剂的浮力变形效应。火焰锋的局部曲率和应变效应是决定燃烧速度的关键因素。微重力实验在不莱梅大学应用空间技术和微重力中心（ZARM）的落塔设施中进行，将提供无浮力火焰传播数据，隔离辐射热损失效应。这些热损失将通过使用高速瑞利散射获得的空间和时间解析火焰温度场来量化。这些发现将有助于开发和修改现有的辐射校正模型，这些模型是针对碳氢化合物开发的，但尚未针对制冷剂火焰进行验证。最后，将进行基于渐近方法和多步反应方案的火焰结构分析，以揭示制冷剂/氧化剂混合物的点火、熄灭和传播所涉及的基本物理化学过程。将研究现有渐近方法的适用性，并将应用针对制冷剂火焰明确定制的修改。这将有助于开发一种准确而稳健的简化建模方法，其中包含制冷剂火焰燃烧速度的近似公式。