Extinction and instability mechanisms of premixed turbulent flames

预混湍流火焰的熄灭和不稳定机制

• 批准号: 1236892
• 负责人: Paul Ronney
• 金额: $ 32.7万
• 依托单位: University of Southern California
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1236892&HistoricalAwards=false
• 关键词: Extinction; instability; mechanisms; premixed; turbulent

Experiments will be conducted to develop a more comprehensive understanding of the burning properties of fuel-air mixtures highly diluted with excess air or exhaust gas and thereby obtain knowledge that could be applied to improve the efficiency and reduce harmful emissions from internal combustion engines and other energy conversion devices. Both hydrocarbon-air and hydrogen-air mixtures will be tested; hydrogen is entirely different from other fuels because of its lower minimum flame temperatures supporting combustion, low ratio of mixture thermal diffusivity to fuel mass diffusivity and lower heat losses, which lead to unique flame properties that are difficult to quantify. Three sets of experiments will be performed. First, to study the effects of turbulence, experiments in a jet-stirred combustion chamber will be conducted. Burning rates, conditions for flame extinguishment and emissions will be examined for varying mixtures and turbulence conditions. Second, to assess the effects of flame stretching, the burning rates and shapes of flame edges at the boundary between burning and extinguished regions of the flames will be studied in a turbulence-free apparatus. Third, to study the effects thermal expansion without hydrodynamic strain (other than that generated by self-induced flow), the propagation rates and stability properties of flames propagating in narrow channels (i.e. Hele-Shaw cells) will be studied. This is considered especially relevant since most laboratory experiments are conducted in open apparatuses where thermal expansion is relaxed in the directions parallel to the flame plane, whereas combustion in most practical devices (e.g., IC engines) occurs in very confined geometries where this relaxation cannot occur.The use of fuel-air mixtures (particularly hydrogen-air mixtures) highly diluted with excess air or exhaust gas is an environmentally friendly way of operating internal combustion engines but the ability to employ these mixtures in engines is hindered by the lack of knowledge of the rates at which these flames burn, the flame shapes they produce, and if/when these flames will extinguish. While many hydrogen fueled vehicles use fuel cells, it is still likely that for many applications, internal combustion engines will be the best power system due to the vastly superior power to weight ratio of engines compared to fuel cells even though the engine efficiencies are slightly lower than fuel cells. Moreover, most of harmful emissions concerns of hydrocarbon-fueled engines are practically eliminated using hydrogen fuel. The information obtained in this work will provide a better understanding of combustion of hydrogen, hydrocarbon and hydrogen/hydrocarbon mixtures. This data will be beneficial not only for engine design, but also in reducing fire and explosion hazards associated with fuel manufacturing, transportation and storage. The proposed work will support a graduate student and two undergraduates, the support for one of which is reserved for a member of an under-represented group.

将进行实验，以更全面地了解用过量空气或废气高度稀释的燃料空气混合物的燃烧特性，从而获得可用于提高效率并减少内燃机和其他能源的有害排放的知识转换装置。 碳氢化合物-空气和氢气-空气混合物都将进行测试；氢气与其他燃料完全不同，因为它支持燃烧的最低火焰温度较低，混合物热扩散率与燃料质量扩散率之比较低，并且热损失较低，从而导致难以量化的独特火焰特性。 将进行三组实验。 首先，为了研究湍流的影响，将在喷射搅拌燃烧室中进行实验。 将针对不同的混合物和湍流条件检查燃烧速率、火焰熄灭和排放的条件。 其次，为了评估火焰拉伸的影响，将在无湍流装置中研究火焰燃烧区域和熄灭区域之间边界处的燃烧速率和火焰边缘形状。 第三，为了研究没有流体动力应变（除了自感流产生的）的热膨胀效应，将研究火焰在狭窄通道（即 Hele-Shaw 单元）中传播的传播速率和稳定性。 这被认为特别相关，因为大多数实验室实验是在开放式装置中进行的，其中热膨胀在平行于火焰平面的方向上松弛，而大多数实际装置（例如内燃机）中的燃烧发生在非常有限的几何形状中，在这种几何形状中不能发生这种松弛使用用过量空气或废气高度稀释的燃料-空气混合物（特别是氢气-空气混合物）是一种运行内燃机的环保方式，但由于缺乏对这些混合物的了解，在发动机中使用这些混合物的能力受到阻碍。这些的费率火焰燃烧、它们产生的火焰形状以及这些火焰是否/何时会熄灭。 虽然许多氢燃料汽车使用燃料电池，但对于许多应用来说，内燃机仍然可能是最好的动力系统，因为与燃料电池相比，发动机的功率重量比要优越得多，尽管发动机效率稍低比燃料电池。 此外，使用氢燃料实际上可以消除碳氢燃料发动机的大部分有害排放问题。 这项工作中获得的信息将有助于更好地了解氢气、碳氢化合物和氢气/碳氢化合物混合物的燃烧。 这些数据不仅有利于发动机设计，而且有利于减少与燃料制造、运输和储存相关的火灾和爆炸危险。 拟议的工作将支持一名研究生和两名本科生，其中一名学生的支持是为代表性不足群体的成员保留的。