Novel 3-D Measurements of Flame Index to Solve the Flame Blowout Problem

CBET-1332252James F.理解湍流火焰如何燃烧和熄灭的物理学原理是一个重要但尚未解决的障碍，它限制了燃烧科学领域的进步。为了从固定能源和发动机获得较低的一氧化氮污染物水平和较高的能量效率，需要延长火焰熄灭极限，但首先必须理解基本的物理学。目前，计算设计代码不能预测火焰熄灭极限，因为需要关键的实验数据。该研究项目将通过使用PI最近在以前的NSF项目上开发的新激光诊断进行测量来获得对火焰熄灭问题的新见解。 高速电影将测量高度湍流火焰内的局部气体速度场以及燃料和空气浓度水平。 激光片穿过湍流火焰，高速摄像机以每秒20，000帧的速度记录荧光。 这些图像提供了计算模型所需的基本量的测量结果，包括局部火焰湍流传播速度、空气动力学应变率和火焰指数。这项工作的新颖之处在于，新的激光诊断提供了真实三维火焰传播速度的测量结果。 它们还提供有关发生的燃烧类型的信息，例如燃料和空气已适当预混的位置以及它们以非预混方式燃烧的位置。 高速电影将有助于解释以前无法测量的动态，不稳定的过程。 该方法是系统地改变无量纲的控制参数，然后尝试折叠数据集，以使其适合于一组简单的缩放关系（公式），这将是普遍使用的。高速电影将记录甲醛，丙酮和二氧化氮的荧光，以成像燃料，空气和中间化学物质的浓度。三维测量将通过快速扫描激光片来实现。这项工作的成功将首次导致三维数据，用于理解湍流火焰中的火焰锚定/井喷，这些火焰跨越了预混、部分预混和非预混的整个燃烧区域。 这对于开发设计燃烧装置的代码至关重要。 该研究将进一步实现低排放燃烧（例如，NOx），因为一旦理解了火焰锚定/熄灭机制，燃烧条件就可以被推向尽可能接近稀极限条件，从而导致低温和低水平的NOx。

CBET-1332252James F. DriscollUniversity of MichiganUnderstanding the physics of how a turbulent flame extinguishes and blows out is an important and yet unsolved barrier that limits progress in the area of combustion science. It is desirable to extend the flame blowout limits in order to achieve lower nitric oxide pollutant levels and higher energy efficiency from stationary energy sources and from engines, but first the basic physics must be understood. At present, computational design codes cannot predict flame blowout limits because of the need for critical experimental data. This research project will obtain new insights into the flame blowout problem by making measurements using new laser diagnostics recently developed by the PI on a previous NSF project. High-speed movies will measure the local gas velocity field and the fuel and air concentration levels within a highly turbulent flame. Laser light sheets pass through the turbulent flame and the fluorescence is recorded at 20,000 frames per second by high-speed cameras. The images provide measurements of fundamental quantities that are needed by the computational models, including the local flame turbulent propagation speed, the aerodynamic strain rate and the flame index.The novel aspects of the work are that the new laser diagnostics provide measurements of the true, three-dimensional flame propagation speed. They also provide information about the type of combustion that occurs, such as the locations were the fuel and air have been properly premixed and where they burn in a non-premixed manner. The high-speed movies will help to explain the dynamic, unsteady processes that previously could not be measured. The approach is to systematically vary the non-dimensional governing parameters and then attempt to collapse the data set to fit it to a set of simple scaling relations (formulas) that will be of general use. The high-speed movies will record fluoresecence from formaldehyde, acetone and nitrogen dioxide in order to image the concentrations of fuel, air and intermediate chemical species. Three dimensional measurements will be achieved by rapidly sweeping the laser light sheets.The success of the work will lead to the 3-D data for the first time for understanding flame anchoring/blowout in turbulent flames spanning the whole spectrum of burning regimes premixed, partially premixed, and non-premixed. This is critical for developing codes for designing combustion devices. The study would further enable low-emission combustion (e.g., NOx), because once the flame anchoring/blowout mechanism is understood, the combustion conditions can be pushed toward as close to the lean limit conditions as possible, resulting in low temperatures and low levels of NOx.