Fundamentals of Metal Particle Combustion for Energy and Loss Prevention Applications

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The search for a carbon-free energy source to replace fossil fuels to mitigate global climate change is of paramount importance. Primary electricity cannot be effectively stored or globally traded, so there is a need for non-polluting secondary energy carriers to replace the role that hydrocarbon fuels currently play as energy commodities. The use of hydrogen as an alternative to fossil fuels remains elusive due to the low volumetric storage density of hydrogen and explosion safety problems.****Common metal powders, such as aluminum, magnesium, silicon and iron, are realistic and feasible candidates for use as zero-carbon-emission energy carriers due to their high energy density, inherent safety, abundance, low cost, and the fact that they can be recycled from oxides using existing metallurgical processes. The chemical energy released during metal combustion with air can be used to directly fuel external-combustion Stirling-type engines or run a Rankine cycle for power generation. Furthermore, metal powders can react directly with water to provide a hot hydrogen-steam flow which can be used to power internal-combustion engines, turbines, or fuel cells. The key step in all of these applications is the efficient reaction of metal powder with gases or water. In our laboratory, we have successfully stabilized aluminum and iron metal-powder flames in air and in the products of methane-air combustion. We have also demonstrated that hydrogen may be efficiently produced in an aluminum-water reactor using readily available micron-sized industrial aluminum powders. ****The primary objective of the proposed research program is to build a strong scientific foundation for the basis of a transformative metal-fuel economy that will enable the design and construction of efficient systems to convert the chemical energy stored in metal-powder fuels into power for transportation and power generation applications. The long-term goal will be to develop prototype energy-conversion devices using either a dry (metal-air) or wet (metal-water) conversion cycle. A secondary objective related to loss prevention is to predict and mitigate the effects of metal dust explosions following an accidental large-scale release of metal dust into air.***The research program includes a) identifying the best candidate metals for use as energy carriers using thermodynamic and economic life-cycle analyses, b) studying metal-powder/air flame structures and flame burning rates with optical and laser diagnostics, c) developing models of metal-powder/air flames with predictive capabilities to enable the design of efficient combustors, d) studying metal-water reactions at temperatures up to supercritical-water conditions, and e) studying the combustion of unconfined metal dust-air clouds to determine the effect of scale on the flame speed and radiative properties of large-scale dust-air flames.**