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会发生局部火焰熄灭。 例如，相对于氧化剂的较大燃料速度可能会导致火焰底部产生足够大的标量梯度，从而导致熄灭，而较大的雷诺数可能会导致下游位置的熄灭。 局部熄灭可能会导致从燃烧器升起的稳定火焰，可能导致反应片上出现局部孔，或者可能导致火焰整体熄灭。 局部熄灭的一个共同特征是火焰边缘，它可能会向未燃烧的燃料和空气传播（点燃），也可能会向燃烧产物后退（熄灭）。由于边缘火焰将燃料与空气分离，因此边缘之外可能存在强烈的成分梯度。 已经发展了成分梯度中边缘火焰传播的理论，并且已经对稳定传播火焰进行了一些测量。智力价值该项目通过测量多个反应混合层中的速度和浓度场来解决边缘火焰传播问题。 The measurements provide a complete examination of the effects of mixture and velocity gradients at the flame edge.此外，还首次建立了后退的稳定火焰（负传播速度）并与理论发展进行比较。由于后退和传播边缘火焰对于湍流提升射流火焰和局部熄灭的湍流火焰都很重要，因此所提出的测量允许为湍流火焰的这一重要特征开发更准确和完整的模型。 拉曼散射、瑞利散射、激光诱导荧光和粒子图像测速适用于许多选定火焰的建议几何形状。 这项工作预计将有助于了解反应流和非反应流之间界面的火焰稳定性。更广泛的影响这项研究的潜在重要性在于其对未来工业燃烧器设计的影响，这些设计建议使用局部熄灭或升起火焰来减少污染物的产生。因此，了解边缘火焰并开发湍流中边缘火焰传播模型至关重要。这种发展还影响其他燃烧领域，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）以及固体推进剂的火焰传播。 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. 除了这一研究元素之外，高年级本科生还将设计一个简单的模型燃烧器，用于与当地高中科学教育工作者进行演示。该燃烧室的设计旨在允许对火焰稳定性、燃烧模式以及燃烧在工业中的应用进行讨论和模型演示。