Asymptotic Analyses of Flames with Real Chemistry

用真实化学对火焰进行渐近分析

• 批准号: 9214888
• 负责人: Forman Williams
• 金额: $ 25.78万
• 依托单位: University of California-San Diego
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1992
• 资助国家: 美国
• 起止时间: 1992-11-01 至 1995-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9214888&HistoricalAwards=false
• 关键词: Asymptotic; Analyses; Flames; Real; Chemistry

This program applies asymptotic methods--parameter expansions for large and small values of parameters appearing in differential equations--to the analysis of structures of flames in real combustible mixtures. Rate parameters for elementary chemical steps are taken from literature on chemical-kinetic experiments, and through nondimensionalization of the conservation equations, appropriate large and small parameters are identified. These parameters typically involve activation energies, leading to activation-energy asymptotics, or ratios of reaction rates of elementary steps, yielding rate-ratio asymptotics. Identification of limiting values of the parameters simplifies the conservation equations and allows solutions to be obtained largely analytically, without resort to numerical integration of the full set of conservation equations. The methods typically lead to formulas for the quantities of interest, such as burning velocities and extinction strain rates, and the formulas usually contain parameters determined by numerical integrations of two-point boundary-value problems for ordinary differential equations. Since these equations are much simpler than the starting equations, full parametric solutions are obtained, rather than solutions restricted to specific conditions. As a consequence, better understanding of flame structure is developed, the essential aspects of the combustion process are identified, and non-essential complications that play no significant role are eliminated. This type of approach has been completed in a previous study for the ozone decomposition flame, for methane flames, and for hydrogen flames, for example, yielding good four-step and two-step mechanisms for the last two flames, respectively. The current program will address higher hydrocarbon flames, hydrogen flames containing halogens, flames involving nitrogen chemistry, and methanol flames, as well as addressing issues of intrinsic stability and influences of strain on flames. Special attention will be paid to the derivation of reduced kinetic schemes of use to the practicing engineer in combustion design applications. In addition, the results will contribute to our general knowledge of mechanisms of flame propagation, flame structure, and extinction.

本程序应用渐近方法--对微分方程式中出现的参数值的大小进行参数展开--来分析实际可燃混合物中的火焰结构。基本化学步骤的速率参数取自化学动力学实验的文献，通过对守恒方程的无量纲化，确定了合适的大参数和小参数。这些参数通常涉及活化能，导致活化能渐近，或基本步骤的反应速率比，产生速率比渐近。参数极限值的识别简化了守恒方程，并允许在很大程度上以解析的方式获得解，而不需要对整个守恒方程进行数值积分。这些方法通常会得到感兴趣的量的公式，如燃烧速度和消光应变率，这些公式通常包含由常微分方程组两点边值问题的数值积分确定的参数。由于这些方程比初始方程简单得多，所以得到了完整的参数解，而不是限制在特定条件下的解。结果，更好地了解了火焰结构，识别了燃烧过程的基本方面，消除了不起重要作用的非基本并发症。例如，这种方法在先前对臭氧分解火焰、甲烷火焰和氢火焰的研究中已经完成，分别为最后两个火焰产生了良好的四步和两步机制。目前的方案将解决更高级的碳氢化合物火焰、含卤素的氢火焰、涉及氮化学的火焰和甲醇火焰，以及内在稳定性和应变对火焰的影响问题。将特别注意简化动力学方案的推导，以供实际工程师在燃烧设计应用中使用。此外，这些结果将有助于我们对火焰传播、火焰结构和消光的一般知识。