EAGER: MINIMUM THERMAL CONDUCTIVITY AND THERMAL EXPANSION CERAMIC NANOCOMPOSITES FOR MICROCOMBUSTOR APPLICATION

在微尺度液体燃料燃烧系统中，需要有限体积的燃烧器沿着有限的停留时间用于燃料蒸发和混合。在小规模下，与气体预混合停留时间相比，该时间可能是显著的，因为在低雷诺数下的混合和蒸发通常较差。在常规燃烧室和小型燃烧室中，通常对氧化剂流、燃料流或两者施加涡流，以稳定火焰并扩大熄灭极限。在小尺度下，旋流可以通过切向喷射、旋流叶片或燃烧室横截面积的阶跃增加来提供。 为了使燃烧室的特征长度最小化，需要对低雷诺数下的液滴输运、汽化和混合有基本的了解。该项目的目标是开发高效和无污染的非常小体积的微型燃烧器，可以使用气体和液体燃料。微型示范的成功将使便携式微型发电能够用于便携式设备，如膝上型电脑，也可用于微型推进和微型卫星。该项目旨在开发燃料灵活和高效的微型燃烧器（燃烧体积为0.0018立方英寸）。这种尺寸的燃烧室小于火焰熄灭距离。通过实验和计算得出的基本认识将允许有效的热再循环回到燃烧室，以帮助减轻火焰的热淬火。燃料将通过多孔热回收器注入，以进行预蒸发，并采取措施避免燃料焦化和多孔介质的劣化，这可能限制燃烧室和微型推进器的使用寿命。为了实现项目目标，将开发一系列新颖的任务，并通过实验和计算进行测试，以丰富知识并提供更广泛的应用。该项目将探索开发和存款一种新颖的和创新的陶瓷纳米结构的复合材料的微型燃烧器的内壁具有超低的导热性和近零的热膨胀，使没有或最小的热交换发生在不需要的地方，同时保持高传热的其他墙壁上的反应物预热之前，燃料-空气混合物进入燃烧体积。 具有废气和新鲜反应物混合物之间的有效热交换的有效热管理是至关重要的。同流换热器类型的热交换器将用于废气和进入的新鲜燃料-空气混合物之间的热交换。 对于液体燃料的情况，燃料的汽化将通过多孔热回收器。 重点将放在锆基陶瓷的微型燃烧器的微尺度动力应用。所使用的方法将是制造特殊配置的锆基纳米复合材料，其中可以通过引入多尺度声子散射来改变热导率和膨胀，即，原子（原子尺度）和界面（纳米尺度）的碰撞。超低热导率的纳米颗粒将沉积在燃烧室的限定壁上，以实现接近零的热导率，同时在其他壁上保持高的热交换，以提高效率和性能。该项目将影响用于地面和空间应用的下一代微型燃烧和推进装置的开发。

In micro-scale liquid fuelled combustion systems a finite volume of the combustor along with a finite residence time is required for fuel vaporization and mixing. At the small scale this time can be significant compared to the gaseous premixed residence time because mixing and vaporization at low Reynolds numbers is generally poor. In both conventional and small scale combustors swirl is often imparted to the oxidizer flow, the fuel flow, or both, in order to stabilize the flame and broaden the extinction limits. At the small scale the swirl flow can be provided by tangential injection, swirl vanes, or step increases in the cross sectional area of the combustor. In order to minimize the characteristic length of the combustion chamber a fundamental understanding of droplet transport, vaporization, and mixing at low Reynolds number is required. The project objective is to develop efficient and non-polluting very small volume micro-scale combustor that can be operated with gas and liquid fuels. Successful demonstration at microscale will allow portable micro-power generation for use in portable devices, such as, laptops, and also for applications in micro-propulsion and micro-satellites. The project aims to develop fuel flexible and efficient micro-combustor (combustion volume of the order of 0.0018 cubic inches). Such size combustor is smaller than flame quenching distance. The fundamental understanding developed via experiments and calculations will allow efficient heat recirculation back into the combustor to help alleviate thermal quenching of the flame. The fuel will be injected through a porous heat recuperator for pre-vaporization with measures taken to avoid fuel coking and deterioration of the porous media that can limit the operational life of the combustor and micro-thruster. To achieve the project objectives, set of novel tasks will be developed and tested using experiments and calculations to enrich knowledge and provide wider applications. This project will explore means to develop and deposit a novel and innovative ceramic nanostructured composite materials on inside walls of micro-scale combustor with ultralow thermal conductivity and near-zero thermal expansion so that no or minimal heat exchange occurs where it is not desired while maintaining high heat transfer on the other walls to preheat the reactants prior to fuel-air mixture entering the combustion volume. Efficient thermal management with efficient heat exchange between the exhaust gases and fresh reactant mixture is critical. A recuperator type heat exchanger will be used for heat exchange between the exhaust gases and incoming fresh fuel-air mixture. For the case of liquid fuel the vaporization of fuel will be via porous heat recuperator. The emphasis will be placed on zirconium-based ceramics for micro-combustor for micro-scale power applications. The approach used will be to manufacture specially-configured Zirconium-based nano-composites in which thermal conductivity and expansion can be altered by introducing multi-scale phonon scatters, i.e., rattling atoms (atomic scale) and interfaces (nanometer scale). Nanosize particles of ultralow thermal conductivity will be deposited on defined wall of the combustor for near zero thermal conductivity while maintaining high heat exchange on the other walls to enhance the efficiency and performance. This project will influence the development of next generation miniature scale combustion and propulsion devices for use in terrestrial and space applications.