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，都依赖于将湍急的燃料流注入高温氧化环境。在一定的混合气和温度条件下，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。对于这两种情况中的任何一种，都非常希望了解控制瞬时自动点火过程的物理原理。湍流是非常复杂的，当与控制自燃的化学反应相耦合时，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影响。在这个项目中，将使用先进的激光诊断技术对燃料/氧化剂混合、温度和物种进行时间分辨测量，以表征在湍流燃料喷射下实现自动点火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，从对汽车点火动力学的新的物理理解到评估数值模拟和模型。该项目还将帮助培训一名研究生和指导一名博士后研究员。此外，该项目的一个独特方面是实施了一个正式的从研究生到本科生的直接指导计划，在这个计划中，研究生与本科生荣誉学生合作并指导。国际学生联合会还将与当地一所小学合作开展K-12活动，为年轻学生提供与STEM相关主题的信息、灵感和主动性。最重要的主题，如燃烧、发动机和激光，为年幼的孩子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。所提出的研究将是变革性的，因为湍流混合、低温化学和热化学之间的动态耦合。首次对点火核形成进行了详细研究。高速(10至100 kHz采集率)激光诊断仪将被用来测量通过自动点火的湍流燃油喷射后的混合气分数、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，包括与湍流混合改变自燃拓扑的机理，以及低温化学(例如CH2O)在点火核形成中的作用。由于自燃过程的瞬时性和空间间歇性，需要多维、时间的记录来表征点火核心处的流场标量。这些测量将被用来确定混合气分数、CH2O(低温化学)和OH(热点火核)之间的时空相关性，并开发基于点火核位置的混合物分数、温度和标量耗散的新统计数据，用于对导致自燃的最可能条件的参数化。拟议的测量将在广泛的测试条件下进行，检查不同的雷诺(Damköhler)数、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.