Extinction and instability mechanisms of premixed turbulent flames

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内燃机和其他能源转换装置的效率和减少有害排放的知识。碳氢-空气混合物和氢-空气混合物都将进行测试；氢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，混合物热扩散系数与燃料质量扩散系数的比率较低，热损失较小，这导致了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，将在射流搅拌燃烧室中进行实验。将检查不同混合气和湍流条件下的燃烧速度、灭火条件和排放情况。其次，为了评估火焰拉伸的效果，将在无湍流装置中研究火焰燃烧和熄灭区域交界处的燃烧速度和火焰边缘形状。第三，为了研究无水动力应变的热膨胀效应(不是由自生流动引起的热膨胀)，我们将研究火焰在狭窄通道(即Hele-Shaw槽)中的传播速度和稳定性。这一点被认为特别重要，因为大多数实验室实验是在开放的设备中进行的，其中热膨胀在平行于火焰平面的方向上松弛，而大多数实际设备(例如内燃机)的燃烧发生在非常有限的几何形状中，在那里不会发生这种松弛。使用燃料-空气混合物(特别是氢-空气混合物)与过量空气或废气高度稀释是操作内燃机的一种环境友好的方式，但由于缺乏对这些火焰燃烧的速度、它们产生的火焰形状以及这些火焰是否/何时会熄灭的知识，在发动机中使用这些混合物的能力受到阻碍。虽然许多氢燃料汽车使用燃料电池，但对于许多应用来说，内燃机仍可能是最好的动力系统，因为与燃料电池相比，内燃机的功率重量比要优越得多，尽管发动机的效率略低于燃料电池。此外，使用氢燃料几乎消除了碳氢燃料发动机的大部分有害排放担忧。在这项工作中获得的信息将有助于更好地了解氢、碳氢化合物和氢/碳氢混合物的燃烧。这些数据不仅有利于发动机设计，还有助于减少与燃料制造、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，其中一人的支助是为任职人数不足的群体的一名成员保留的。

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.