Development of Microcombustors and Characterization of Confined Sub-Millimeter Laminar Diffusion Flames

255 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.This study was motivated by the proliferation of portable electronic devices and the limitations of battery technology to meet the escalating power demands of such devices. Several battery replacement technologies intended to tap the massive energy densities of liquid chemical fuels have been proposed, and many of these require the use of combustion for its rapid and efficient conversion of chemical energy to heat. To enable such devices on smaller length scales, engineering challenges to microscale combustion must be solved. Presented herein are advances in the design and performance of microscale hydrocarbon combustion devices and fundamental studies of microscale flame structure. A simple, robust, high endurance, high efficiency sub-millimeter hydrocarbon microscale combustor capable of producing an estimated 400W-cm-3 was built by reducing heterogeneous reactions in the combustor, tailoring the flow pattern of the fuel and oxidizer, and properly insulating the combustor to limit heat loss. A four-step surface treatment scheme was developed to mitigate radical quenching on poly-crystalline alpha-alumina surfaces. A laminar diffusion flame structure consisting of a column of cellular edge flames aligned in the direction of flow was discovered and is believed to be novel to the microscale. Characterization of the dynamics of this flame structure showed that the structure was heavily influenced by fuel and oxidant composition and transport properties. The cellular structure was determined to arise via a mass transfer-limited mechanism. The structure, intensity, and spacing of the flame cells were also shown to be highly sensitive to heat transfer effects. The developed burner and fundamental discoveries on microscale flame structure are important developments in the microscale power generation field.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD