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.

实用燃烧器中的非固定火焰通常被操作，以使火焰的局部灭绝发生。 例如，相对于氧化剂的较大燃料速度可以在火焰底部导致足够大的标量梯度导致灭绝，并且大雷诺数可以导致下游位置灭绝。 局部灭绝会导致从燃烧器提起的稳定火焰，可能导致反应表中的局部孔，或者可能导致火焰的全局灭绝。 局部灭绝的一个共同特征是火焰边缘，它可能朝着未燃烧的燃料和空气（点火）传播，或者可能退出燃烧产物（灭绝）。由于边缘火焰将燃料与空气分开，因此可以在边缘之外存在强大的组成梯度。 已经开发了成分梯度中边缘火焰传播的理论，并进行了一些稳定传播火焰的测量。智力优点这个项目通过测量众多反应混合层中的速度和浓度场来解决边缘flame的传播。这些测量结果对火焰边缘的混合物和速度梯度的影响进行了完整的检查。此外，还建立了退缩的稳定火焰（负繁殖速度），并首次与理论发展进行了比较。由于向后的和传播的边缘对具有局部灭绝的湍流升起火焰和湍流火焰都很重要，因此提出的测量允许开发更准确，更完整的模型，以实现湍流火焰的这一重要特征。 在许多选定的火焰中，将拉曼散射，雷利散射，激光诱导的荧光和粒子图像速度法应用于所提出的几何形状。 预计这项工作将在反应和非反应流之间的接口上提供对火焰稳定性的理解。这项研究更广泛地影响了其对未来工业燃烧器设计的影响，该设计建议使用局部灭绝或举起火焰来减少污染物的产量。因此，对边缘火焰的理解和湍流中边缘炉繁殖模型的发展至关重要。这种发展还影响了其他燃烧区域，包括火焰散布在液体和固体表面上（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。 本科生通过加速的硕士学位参与。在机械工程系中的计划，并通过直接的本科助理制度。 本科生专注于仅检查少数测试条件的短期项目。 除了这一研究元素外，高级本科生还将设计一个简单的模型燃烧器，可与当地的高中科学教育者一起演示。该燃烧器将旨在允许讨论和模型演示火焰稳定性，燃烧方式以及在行业中燃烧的应用。