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

1605136 - 萨顿运输和发电平台等广泛的工程系统依赖于将湍流燃料流注入高温氧化环境。 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发动机/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/或灾难性损坏。 对于这两种情况中的任何一种，都非常需要了解控制瞬态自燃过程的物理原理。 湍流非常复杂，当与控制自燃的化学反应耦合时，会形成一个高度动态的系统，其中湍流混合对化学反应有直接影响。 在该项目中，将使用先进的激光诊断技术对燃料/氧化剂混合、温度和物质进行时间分辨测量，表征在湍流燃料喷射下实现自燃内核形成所需的流量和化学条件。 这项研究的影响将是深远的，从对自燃动力学的新物理理解到评估数值模拟和模型。 该项目还将帮助研究生的培训和博士后研究员的指导。 此外，该项目的一个独特之处是实施了正式的直接研究生到本科生指导计划，其中研究生与本科生荣誉学生合作并指导。 该 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。 燃烧、发动机和激光等首要主题为年幼的孩子提供了令人兴奋的主题，并有助于为他们对科学和技术的终生兴趣奠定基础。 所提出的研究将具有变革性，因为湍流混合、低温化学和“热”之间的动态耦合。将首次详细研究点火内核的形成。 高速（10 至 100 kHz 采集速率）激光诊断将用于测量通过自点​​火进行湍流燃料喷射后的混合分数、温度和 CH2O/OH 浓度。 具体的研究贡献包括对导致观察到的自燃拓扑的关键时间相关过程的量化，包括湍流混合改变自燃拓扑的机制以及低温化学物质（例如 CH2O）对点火内核形成的作用。由于自燃过程的瞬态和空间间歇性，需要多维、时间记录来表征点火核心位置的流场标量。 这些测量将用于确定混合分数、CH2O（低温化学）和 OH（热点火内核）之间的时空相关性，并开发以点火内核位置为条件的混合分数、温度和标量耗散的新统计数据，以对导致自燃的最可能条件进行参数化。 拟议的测量将在广泛的测试条件下进行，检查不同雷诺数（Damköhler）、燃料类型以及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.