CAREER: Controlling Mechanisms of Dust Layer Ignition and Flame Propagation in Dust Clouds

0846764 rangwala该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。这项职业奖的研究重点是发展对粉尘火灾和爆炸的基本科学理解。可燃性粉尘层可以被温度足够高的表面点燃，由此产生的火灾可能造成巨大的生命和财产损失。在某些情况下，这些过程是逐步升级的事件链的第一步，这些事件链可能导致气体和粉尘爆炸。由于固体颗粒与气体火焰锋面的相互作用，粉尘爆燃的发生和传播是一种极其复杂的现象。与预混气体爆燃相比，粉尘-氧化剂爆燃取决于挥发物的演化速率、这些挥发物与颗粒周围氧化剂的混合、颗粒与气相氧化的耦合以及火焰与周围环境之间的辐射能量交换。为了确定粉尘层点火和爆燃的机制和控制参数，正在进行详细的实验，以测量不同燃料/氧化剂比例、颗粒大小和粉尘类型下粉尘-氧化剂火焰的点火和传播速率。在其中一部分工作中，将使用改进的ASTM E2021热表面设备来分析控制粉尘层点火的参数。然后，这些参数将用于预测灰尘沉积物在现实几何形状（如二维楔形和三维角）中的点火。分析了粉尘粒径和氧浓度对粉尘层着火的影响。同时，还将探讨粉尘-氧化剂预混火焰的结构，以分析颗粒流中火焰的传播。一个预混马赫赫布拉燃烧器与适当的修改，以允许燃烧均匀的混合物粉尘和氧化剂将用于研究稳定的粉尘-氧化剂火焰的结构。通过激光多普勒风速测量法测量的层流燃烧速度将用于表征石松（30微米）、聚甲基丙烯酸甲酯（300nm、10微米、30微米和60微米）、煤（15-38微米、38-44微米和44- 55微米）和铝（10微米）粉末的质量燃烧速度。该实验研究结果将进一步用于验证火焰在尘埃云中传播的数值CFD模型。这项研究也意味着作为一个催化剂，在火灾科学与工程领域的基础研究的新机会。该教育计划将从两个方面提高全世界中小学和大学对火灾科学与工程学科的认识：(a)设立国家和国际项目中心，以本科生为重点，在与火灾有关的基础研究领域进行为期三个月的独立学习小组；(b)与当地高中和初中教师互动，为学生制定为期三周的暑期课程，以培养他们对基础科学的兴趣。学生们将在WPI消防实验室获得实践经验，并向当地消防员学习消防安全知识。本建议的教育努力有望提高对火灾科学领域的认识，而研究计划将有助于从目前基于工程的经验模型转向基于基础理论的分析和实验。

0846764RangwalaThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This research in this CAREER award focuses on developing fundamental scientific understanding of dust fires and explosions. Combustible dust layers can be ignited by a surface whose temperature is sufficiently high and the resulting fires can cause large losses in lives and property. In some cases these processes are the first step towards an escalating chain of events that can lead to both gas and dust explosions. Initiation and propagation of dust deflagrations are extremely complex phenomena due to the interaction between solid particles and the gaseous flame front. In comparison with premixed gas deflagration, a dust-oxidizer deflagration depends on the rate of evolution of volatiles, the mixing of these volatiles with the oxidizer surrounding the particles, coupling of the particles and gas-phase oxidation, and radiative energy exchange between the flame and its surroundings.To identify mechanisms and controlling parameters for dust-layer ignition and deflagration, detailed experiments are being developed to measure ignition and the rate of propagation of a dust-oxidizer flame with different fuel/oxidizer ratios, particle sizes, and dust types. In one part of the work, a modified ASTM E2021 hot-surface apparatus will be used to analyze parameters controlling the ignition of dust layers. These parameters will then be used to predict ignition of a dust deposit in a realistic geometry such as a two-dimensional wedge and a three-dimensional corner. Influence on particle size and oxygen concentration on dust layer ignition will also be analyzed. In parallel, the structure of a premixed dust-oxidizer flame will be explored to analyze flame propagation in particle-laden flows. A premixed Mache Hebra burner with suitable modifications to allow burning of a homogenous mixture of dust and oxidizer will be used to study the structure of a stabilized dust-oxidizer flame. Laminar burning velocity measured by Laser Doppler Anemometry will be used to characterize the mass burning rate of Lycopodium (30 µm), polymethyl methacrylate (300nm, 10µm, 30µm, and 60µm), coal (15-38µm, 38-44 µm and 44- 55µm), and aluminum (10µm) powders. The results of this experimental study will be further used to validate numerical CFD models for flame propagation in dust clouds.The research is also meant to act as a catalyst for new opportunities of fundamental research in the field of fire science and engineering. The education plan will increase the awareness in schools and universities world-wide toward the discipline of fire science and engineering in two ways: (a) Establishing national and international project centers focused towards undergraduate students for three-month independent study groups in areas of fundamental fire-related research and (b) Interacting with local high-school and middle-school teachers to develop a three-week summer course for their students to generate an interest in basic science. Students will get hands-on experience at the WPI fire laboratory and learn about fire safety from local firefighters. The educational efforts of this proposal are expected to increase awareness of the field of fire science, while the research program will help in bringing a shift from the present engineering-based empirical models to fundamental theory-based analysis and experimentation.