CAREER: Steady and Transient Dynamics of Catalyst-Assisted Combustion in Micro-Scale Power Generators

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

A major limitation to the wide use of MEMS and other micro-scale devices is the availability of suitable power sources. Combustion is an attractive power source because of its high energy density, but there are major technical challenges including ignition from cold start and control of sustained combustion. Given the high surface-to-volume ratio inherent in a microcombustor, there is attraction in using heterogeneous catalytic reactions to promote ignition and to extend flammability limits. This is a computational and experimental study of the physical and chemical processes relevant to this strategy. Advanced computational methods are developed and validated with experimental measurements and parametric studies are done specifically targeted at small-scale combustion systems. Two canonical configurations are studied. First, stagnation-point flow over a catalytic surface is analyzed by modifying existing transient one-dimensional stagnation-point flow code with detailed surface and gas-phase chemical kinetics. Parametric studies address various combustion regimes, modified ignition and extinction limits due to catalytic reaction, and overall combustion performance. Also, the effects of transient modulation of the surface temperature and inlet flow are investigated as a potential control methodology. Second, a microchannel combustor is modeled by developing a high-fidelity multidimensional direct simulation code providing detailed temporal and spatial information on the combustor process. The feasibility of a nonpremixed combustion mode (using a coaxial supply of fuel and oxidizer) as a means of enhancement of ignition and heat generation is assessed. For both configurations, experimental measurements of temperature distribution and product species compositions are compared with computational results to validate embedded submodels. As an education program, interactive computational fluid dynamics (CFD) tools are designed for undergraduate and graduate students in thermo-fluid sciences. These include application packages that are compatible with widely used kinetic simulation packages and web-based tools for solving differential equations and simulating data on reacting flows.