Browsing by Subject "Reaction bonded"

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Additively manufactured Si-SiC combustion devices : the role of heat recirculation in counter-flowing reactors
(2021-07-24) Radyjowski, Patryk Pawel; Ellzey, Janet L.; Bourell, David; Kovar, Desiderio; Belmont, Erica L
The importance of energy efficiency demands novel approaches to combustion of fossil fuels. Significant research has focused on increasing efficiency, reducing emissions, and improving fuel flexibility. One approach of recycling energy from the flame to the reactants, called excess enthalpy combustion, offers all of these potential advantages. A variety of heat recirculating reactor designs exist, but they are all characterized by small pores or channels to maximize the exposure of hot walls to the flowing reactants. This requires a material that can withstand the combustion environment without constraining possible geometries. Standard materials such as ceramics and superalloys are limited in either one or the other of these criteria. A potential solution is an additively manufactured ceramic-metal composite, siliconized silicon carbide (Si-SiC) cermet. It can be fabricated in the desired shape and withstands temperatures up to 1400°C. This work examines the fabrication of Si-SiC parts by a multi-step process including laser sintering, transient binder processing, and metal infiltration. Modifications in the process improved intermediate handling and part quality. Future material science development of manufacturing method could lead to a 1900°C capable material. The newly developed material was investigated under a lean methane-air combustion environment. Flame compatibility and good thermal oxidation above 1200°C were confirmed in the isolated exposure tests. Using the AM process above, three counter-flow combustors were manufactured with different channel geometries such that the surface area to volume ratio was varied. The relationship between the resulting change in heat transfer and the stable operating range was investigated. Higher heat recirculation increased internal temperatures and improved flame stability. The role of heat recirculation was crucial under high speed, high firing rate conditions. Experimental findings were supported by analytical modeling and previous research in the field. CO and NO [subscript x] emissions registered at exits were low, substantially below equilibrium. The material degradation of Si-SiC was tracked over an entire 80-hour period. The operation near 1400°C resulted in partial melting and protrusions of infiltrating metal. Otherwise, passive oxidation was observed to happen in-line with the literature. The new material system for high-temperature applications shows significant potential for the development of new combustor designs.