Catalytic Combustion of Ethanol and Butanol

Report No. ARL-TN-0374
Authors: Douglas A. Behrens and Ivan C. Lee
Date/Pages: September 2009; 22 pages
Abstract: The combustion of energy dense liquid fuels in a catalytic micro-combustor is an attractive alternative to cumbersome batteries. To miniaturize the reactor, I developed an evaporation model to calculate the minimum distance required for complete droplet vaporization. By increasing the ambient temperature from 298 K to 325 K, the distance required for complete evaporation of a 6.5 micron droplet decreases from 3 to 0.15 cm. A platinum mesh acted as a baseline measurement and demonstrated 75% conversion of ethanol. I then selected a more active rhodium-coated alumina foam with a larger surface area and attained 100% conversion of ethanol and 95% conversion of butanol under fuel lean conditions. Effluent post-combustion gas analysis showed that varying the equivalence ratio results in two distinct regimes. A regime of high carbon selectivity for CO2 occurs at low equivalence ratios and corresponds to complete combustion with a typical temperature of 775 K that is ideal for PbTe thermoelectric devices. Conversely, for equivalence ratios greater than 1, carbon selectivity for CO2 decreases and hydrogen production increases. By tuning the equivalence ratio, I have shown that a single device can combust completely for thermoelectric applications, or operate as a fuel reformer to produce hydrogen gas for fuel cells.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2009