CAREER: Characterization of Propagating and Receding Flame Edges in Composition and Velocity Gradients

职业：成分和速度梯度中传播和后退火焰边缘的表征

• 批准号: 0235114
• 负责人: Michael Renfro
• 金额: $ 41.8万
• 依托单位: University of Connecticut
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-02-01 至 2009-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0235114&HistoricalAwards=false
• 关键词: CAREER; Characterization; Propagating; Receding; Flame

Non-premixed flames in practical combustors are often operated such that local extinction of the flame occurs. For example, large fuel velocities relative to the oxidizer can lead to sufficiently large scalar gradients at the flame base to cause extinction, and large Reynolds numbers can lead to extinction at downstream locations. Localized extinction can result in stable flames that are lifted from the burner, can result in local holes in the reaction sheet, or can lead to global extinction of the flame. A common feature of localized extinction is a flame edge, which may either propagate toward unburned fuel and air (ignition) or may recede toward combustion products (extinction). Because the edge flame separates fuel from air, a strong composition gradient can exist beyond the edge. Theories for the propagation of edge flames in composition gradients have been developed, and a few measurements of stable propagating flames have been made. Intellectual meritThis project addresses edge-flame propagation through measurements of velocity and concentration fields in numerous reacting mixing layers. The measurements provide a complete examination of the effects of mixture and velocity gradients at the flame edge. In addition, stable flames that recede (negative propagation velocities) are established and compared to theoretical developments for the first time. Since both receding and propagating edge flames are important to turbulent lifted jet flames and turbulent flames with localized extinction, the proposed measurements permit development of a more accurate and complete model for this important feature of turbulent flames. Raman scattering, Rayleigh scattering, laser-induced fluorescence, and particle image velocimetry are applied to the proposed geometry for many selected flames. The work is expected to provide an understanding of flame stability at interfaces between reacting and nonreacting flows. Broader impactsThis study draws its potential importance from its impact on future industrial combustor designs that propose to use local extinction or lifted flames to reduce pollutant production. Therefore, an understanding of edge flames and the development of models for edge-flame propagation in turbulent flows are critically important. This development also impacts other areas of combustion including flame spread over liquid and solid surfaces (which may be the result of unwanted fire) and flame propagation with solid propellants. Undergraduates are involved through the accelerated M.S. program in the Department of Mechanical Engineering, and through direct undergraduate assistantships. The undergraduates focus on short-duration projects that examine only a few test conditions. In addition to this research element, senior undergraduates will design a simple model combustor to be used for demonstrations with local high-school science educators. This combustor will be designed to allow for discussion and model demonstrations of flame stability, modes of combustion, and the application of combustion in industry.

实际燃烧器中的非预混火焰通常操作成使得发生火焰的局部熄灭。 例如，相对于氧化剂的大的燃料速度可导致火焰基部处的足够大的标量梯度以引起熄灭，并且大的雷诺数可导致下游位置处的熄灭。 局部熄灭可导致从燃烧器升起的稳定火焰，可导致反应板中的局部孔，或可导致火焰的全局熄灭。 局部熄灭的一个共同特征是火焰边缘，它可以向未燃烧的燃料和空气传播（点火），也可以向燃烧产物后退（熄灭）。因为边缘火焰将燃料与空气分离，所以在边缘之外可以存在强的成分梯度。 边缘火焰在成分梯度中传播的理论已经发展起来，并且对稳定传播的火焰进行了一些测量。该项目通过测量许多反应混合层中的速度和浓度场来研究边缘火焰的传播。测量提供了一个完整的检查的混合物和速度梯度在火焰边缘的影响。此外，稳定的火焰后退（负传播速度）的建立和理论发展相比，第一次。由于后退和传播的边缘火焰是重要的湍流提升射流火焰和湍流火焰与局部熄灭，建议的测量允许开发一个更准确和完整的模型，湍流火焰的这一重要特征。 拉曼散射，瑞利散射，激光诱导荧光，粒子图像测速被施加到许多选定的火焰的拟议的几何形状。 这项工作预计将提供反应和非反应流之间的界面处的火焰稳定性的理解。更广泛的影响本研究从其对未来工业燃烧室设计的影响中得出其潜在的重要性，这些设计建议使用局部熄灭或提升火焰来减少污染物的产生。因此，了解边缘火焰和湍流中边缘火焰传播模型的发展至关重要。这一发展也影响了燃烧的其他领域，包括液体和固体表面上的火焰传播（这可能是不必要的火灾的结果）和固体推进剂的火焰传播。 本科生通过加速MS参与。计划在机械工程系，并通过直接本科助教。 本科生专注于只检查少数测试条件的短期项目。 除了这个研究元素，高年级本科生将设计一个简单的模型燃烧器用于演示与当地高中科学教育。该燃烧器的设计将允许对火焰稳定性、燃烧模式以及燃烧在工业中的应用进行讨论和模型演示。