Design and Characterization of a Liquid-Fueled Micro-Combustor

Abstract

As part of an effort to develop a microscale gas turbine engine, this paper presents the design and experimental characterization of a micro-combustor that catalytically burns JP8 fuel. Due to the high energy densities of hydrocarbon fuels, mi-croscale heat engines based on them may enable compact power sources with specific energies higher than those of current battery systems. In addition, utilizing a commonly available logistics fuel would provide advantages for military applications. Thus, a microscale engine burning JP8 fuel is attractive as a portable power source. A liquid-fueled micro-combustor with a combustion chamber volume of 1.4 cm 3 and an overall die size of 36.4 mm × 36.4 mm × 6.5 mm was designed, micro-fabricated, and experimentally characterized. Two configurations were tested and compared; one with the combustion chamber entirely filled with a catalyst, and the other with the combustion chamber partially filled with a catalyst. In the configuration filled with a catalyst, JP8 combustion was sustained at mass flow rates up to 0.1 g/sec, and an exit gas temperature of 780 K; an overall combustor efficiency of 19%, and a power density of 43 MW/m 3 were achieved. The primary limitation on increasing the mass flow rates and temperature further was structural failure of the device due to thermal stresses. With the partially-filled configuration, a mass flow rate of 0.2 g/sec, and a corresponding power density of 54 MW/m 3 were obtained. The exit gas temperature for the partially-filled configuration was as high as 720 K, and the maximum overall efficiency was over 22%. Although the reduced amount of catalyst led to incomplete combustion, smaller thermal losses resulted in an increase in the overall combustor efficiency and power density. A non-dimensional operating map was constructed based on the experiment, and it suggests that improving the thermal efficiency would be necessary to achieve higher efficiencies in the device.