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

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。这一职业奖项的研究重点是发展对尘埃火灾和爆炸的基本科学理解。温度足够高的表面可能会引燃可燃粉尘层，由此产生的火灾会造成巨大的生命和财产损失。在某些情况下，这些过程是迈向一系列不断升级的事件的第一步，这些事件可能导致气体和尘埃爆炸。由于固体颗粒与气体火焰锋面的相互作用，粉尘爆燃的起爆和传播是极其复杂的现象。与预混气体爆燃相比，粉尘氧化剂爆燃取决于挥发物的挥发速率、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。为了确定粉尘层着火和爆燃的机理和控制参数，正在进行详细的实验，测量不同燃料/氧化剂比、颗粒尺寸和粉尘类型的粉尘氧化剂火焰的点火和传播速度。在工作的一部分，将使用改进的ASTM E2021热表面装置来分析控制粉尘层着火的参数。然后，这些参数将被用来预测现实几何形状中的尘埃沉积的着火，例如二维楔形和三维角。分析了颗粒大小和氧气浓度对粉尘层着火的影响。同时，将探索预混粉尘-氧化剂火焰的结构，以分析火焰在颗粒流中的传播。预混的MachheHebra燃烧器经过适当的改进，可以燃烧均匀的粉尘和氧化剂混合物，用来研究稳定的粉尘氧化剂火焰的结构。用激光多普勒测速仪测量的层流燃烧速度将用于表征石棉(30微米)、聚甲基丙烯酸甲酯(300 nm、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)粉末的质量燃速。这项实验研究的结果将进一步用于验证火焰在尘埃云中传播的CFD数值模型。这项研究也将成为火灾科学和工程领域基础研究的新机会的催化剂。该教育计划将通过两种方式提高世界各地的中小学和大学对消防科学与工程学科的认识：(A)建立以本科生为重点的国家和国际项目中心，在与火灾相关的基础研究领域开展为期三个月的独立学习小组；(B)与当地高中和中学教师互动，为他们的学生开发一个为期三周的暑期课程，以激发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。这项提议的教育努力预计将提高人们对火灾科学领域的认识，而研究计划将有助于将目前基于工程的经验模型转变为基于基本理论的分析和实验。

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.