Coupled Mixing and Auto-Ignition Dynamics of Turbulent Fuel Jets Issuing into Hot and Vitiated Oxidizing Environments

1605136 - sutton广泛的工程系统，如运输和发电平台依赖于向高温氧化环境中喷射湍流燃料流。在一定的混合物和温度条件下，会发生自燃。柴油发动机和高速超燃冲压/冲压发动机等系统依靠自动点火来实现点火和火焰稳定。其他系统，包括燃气轮机和火花点火发动机，旨在防止自动点火，以避免重大和/或灾难性的损害。对于这两种情况，都非常需要了解控制瞬态自燃过程的物理原理。湍流是非常复杂的，当与控制自燃的化学反应相结合时，形成了一个高度动态的系统，其中湍流混合对反应化学有直接的影响。在这个项目中，将使用先进的激光诊断技术进行燃料/氧化剂混合、温度和种类的时间分辨测量，表征湍流燃料喷射下实现自燃核形成所需的流动和化学条件。这项研究的影响将是深远的，从对自动点火动力学的新的物理理解到评估数值模拟和模型。该项目还将有助于培养一名研究生和指导一名博士后研究员。此外，这个项目的一个独特之处在于实施了一个正式的直接从研究生到本科生的指导计划，在这个计划中，一名研究生与一名本科优等生合作并指导一名本科生。PI还将与当地一所小学合作开展K-12外展活动，为年轻学生提供stem相关主题的信息、灵感和主动性。主要的主题，如燃烧、发动机和激光，为年幼的孩子们提供了令人兴奋的主题，并有助于为终身对科学和技术的兴趣奠定基础。所提出的研究将具有变革性，因为湍流混合，低温化学和高温化学之间的动态耦合。我们将首次详细研究点火核的形成。高速（10至100 kHz采集速率）激光诊断将用于测量通过自动点火湍流燃油喷射后的混合物分数、温度和CH2O/OH浓度。具体的研究贡献包括量化导致观察到的自燃拓扑的关键时间依赖过程，包括湍流混合改变自燃拓扑的机制以及低温化学（例如CH2O）对点火核形成的作用。由于自燃过程的瞬态和空间间歇性，需要多维的时间记录来表征点火核点的流场标量。这些测量将用于确定混合物分数，CH2O（低温化学）和OH（热点火核）之间的时空相关性，并开发新的混合物分数，温度和标量耗散的统计数据，这些统计数据取决于点火核的位置，从而参数化导致自燃的最可能条件。提议的测量将在广泛的测试条件下进行，检查不同雷诺数（Damköhler）、燃料类型、氧化剂成分和温度的影响。

1605136 - SuttonA broad range of engineering systems such as transportation and power-generation platforms rely on the injection of a turbulent fuel stream into a high-temperature, oxidizing environment. Under certain mixture and temperature conditions, auto-ignition will occur. Systems such as diesel engines and high-speed scramjets/ramjets rely on auto-ignition for achieving ignition and flame stabilization. Other systems, including gas-turbine and spark-ignition engines are designed to prevent auto-ignition to avoid significant and/or catastrophic damage. For either of these scenarios it is highly desired to understand the physics governing the transient auto-ignition process. Turbulent flows are very complex and when coupled to the chemical reactions governing auto-ignition, a highly dynamic system is formed where turbulent mixing has a direct effect on the reaction chemistry. In this project, time-resolved measurements of fuel/oxidizer mixing, temperature, and species will be made using advanced laser diagnostics, characterizing the flow and chemical conditions necessary for achieving auto-ignition kernel formation under turbulent fuel injection. The impact of the research will be far-reaching, ranging from a new physical understanding of auto-ignition dynamics to assessing numerical simulations and models. This project also will aid in the training of a graduate student and mentoring of a post-doctoral researcher. In addition, a unique aspect of this project is the implementation of a formal direct graduate-to-undergraduate mentoring program, where a graduate student is partnered with and mentors an undergraduate honors student. The PI also will partner with a local elementary school for K-12 outreach, equipping young students with information, inspiration, and initiative in STEM-related topics. The overarching topics, such as combustion, engines, and lasers, provide exciting themes for younger children and can help build the foundation for a life-long interest in science and technology. The proposed research will be transformative in the fact that the dynamic coupling between turbulent mixing, low-temperature chemistry and ?hot? ignition kernel formation will be examined in detail for the first time. High-speed (10 to 100 kHz acquisition rate) laser diagnostics will be used to measure the mixture fraction, temperature, and CH2O/OH concentrations following turbulent fuel injection through auto-ignition. Specific research contributions include quantification of key time-dependent processes which lead to the observed auto-ignition topology including the mechanisms in with turbulent mixing modifies auto-ignition topology and the role of low-temperature chemistry (e.g., CH2O) on ignition kernel formation. Due to the transient and spatially-intermittent nature of the auto-ignition process, multi-dimensional, temporal records are necessary to characterize the flow field scalars at the ignition kernel sites. These measurements will be used to determine space-time correlations between mixture fraction, CH2O (low-temperature chemistry) and OH (hot ignition kernel) as well develop new statistics of the mixture fraction, temperature, and scalar dissipation conditioned on the ignition kernel location for parameterization of the most probable conditions leading to auto-ignition. The proposed measurements will be carried out across a broad range of test conditions, examining the effects of varying Reynolds (Damköhler) number, fuel type, and oxidizer composition and temperature.