CAREER: Physics and modeling of flame extinction in presence of evaporating droplets

对火焰熄灭的基本认识在促进能源安全、环境可持续性、航空旅行安全和及时灭火方面发挥着核心作用。近几十年来，国际燃烧界对火焰熄灭进行了广泛的研究，但基础研究的范围大多局限于气态火焰。液滴在实际燃烧系统中是普遍存在的，例如航空燃烧器中的燃油喷雾和减少污染物或灭火中的水滴。当与已建立的气体火焰相互作用时，液滴通过蒸发、稀释、后续反应、湍流调制和辐射传热等物理过程引入额外的机制来熄灭火焰。因此，本项目的主要目的是对液滴存在时控制火焰熄灭过程的关键因素进行基本理解和定量描述。该项目还将包括重要的教育活动，包括一个新的“虚拟热流体实验室”课程和一本由研究数据支持的配套书籍。与研究和教育活动相结合，将实施两项外展计划。首先，一项针对高中教师的教育计划将使用研究数据作为提高高中学生计算素养的独特途径。其次，研究人员将与当地博物馆馆长合作，展示来自研究项目的艺术设计，并吸引代表性不足的群体进入STEM职业。该项目的目标是解决有关非均质热、动量和传质影响火焰熄灭极限的机制的知识差距。随机液滴负载湍流引入了额外的散热器/源和非均匀反应性，以达到接近消光极限的微妙平衡。一个典型的逆流配置将被用来表示火焰-液滴相互作用的基本过程。将采用开源计算框架，其中将仔细设计数值算法，以确保各种物理过程之间的必要耦合。所提出的数值模型和求解算法将结合湍流多相流和消光化学研究的最新发展，为更准确深入的计算研究铺平道路。将建立一种方法，将三维直接数值模拟信息与一维模拟湍流模拟相结合，以实现高效可靠的参数分析。利用降阶模型，建立尺度关系，定量描述这类问题的关键时间尺度和长度尺度。该项目的成功实施将在工程应用中实现鲁棒的降阶建模，例如航空燃烧器的稀薄吹出和使用水雾灭火。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Fundamental understanding of flame extinction plays a central role in promoting energy security, environmental sustainability, air-travel safety and opportune fire suppression. Flame extinction has been extensively studied by the international combustion community in the past few decades, however, the scope of fundamental studies has mostly been limited to gaseous flames. Droplets, such as fuel sprays in aeronautical combustors and water droplets in pollutant reduction or fire suppression, are ubiquitous in practical combustion systems. When interacting with an established gaseous flame, droplets introduce additional mechanisms to extinguish a flame, through physical processes such as vaporization, dilution, subsequent reactions, modulation of turbulence, and radiative heat transfer. Therefore, the principal aim of this project is to provide a fundamental understanding and a quantitative description of key factors governing the flame extinction process in presence of droplets. The project will also encompass significant educational activities, including a new “Virtual Thermal Fluids Lab” course and a companion book that are enabled by the research data. In conjunction with the research and educational activities, two outreach programs will be implemented. First, an educational program for high school teachers will use the research data as a unique avenue to enhance the computational literacy of high school students. Second, researchers will work with local museum curators to showcase artistic designs that are derived from the research program and to attract underrepresented groups into STEM careers. The goal of this project is to address the knowledge gap pertaining to the mechanism through which heterogeneous heat, momentum, and mass transfer impact the extinction limits for flames.Stochastic droplet-laden turbulent flow introduces additional heat sinks/sources and nonuniform reactivity to the delicate balance near the extinction limit. A canonical counterflow configuration will be adopted to represent the fundamental processes of flame-droplet interactions. An open-source computational framework will be adopted, where numerical algorithms will be carefully designed to ensure necessary coupling between various physical processes. The proposed numerical models and solution algorithms will incorporate latest development from the study of turbulent multiphase flows and extinction chemistry, paving the way for more accurate in-depth computational studies. A methodology will be established to combine information from three-dimensional direct numerical simulations with one-dimensional modeled turbulent simulations to enable efficient and reliable parametric analysis. Using the reduced-order models, scaling relations will be established, which will provide a quantitative description of critical time and length scales in such problems. Successful execution of this project will enable robust reduced-order modeling in engineering applications, such as lean-blowoff in aeronautical combustors and fire suppression using water mists.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.