Practical Applications for Emerging Plasma-Assisted Combustion Technology

Various low-temperature plasma approaches, such as microwave applicators, dielectric barrier discharges, and gliding-arc discharges have demonstrated promise for effective plasma-assisted combustion. By application of plasma-excitation to the flame zone, or to the fuel/oxidizer injection streams, electronically-excited molecules and atoms are introduced, enabling flame maintenance for normally unstable flame conditions. If such devices are matured, optimized, and proven on infrastructure-compatible fuels, there is potential for expanding operational ranges, lowering fuel consumption, and improving heat release, as well as reducing pollution in industrial applications. This proposal explores innovative techniques of plasma-excitation applied to combustion flows using magnetically-guided atmospheric discharges as a core technology. Researchers have recently applied this technique to vortex generation for aerodynamic flow control. In one approach, a constricted glow discharge (arc-filament) is generated in the gap of coaxial electrodes positioned in the field of a strong rare-earth magnet. Drift motion of charged particles in the magnetic field results in the production of a Lorentz force, such that the filament sweeps about the center of the coaxial electrodes. To observers, this takes on the apparent form of a plasma “disc” at the tip of the coax. Plasma-assisted combustion is achieved, by replacing the coax barrier with dielectric channels through which fuel and oxidizer are injected, electronically-excited, and mixed in the wake of the plasma filament. The approach effectively combines action of gliding arc types with swirled flow reactors. Further research goals are to catalog fundamental behaviors of this core concept, benchmark performance of novel designs with comparison to alternatives, and define practical approaches for integration into commercial burners. In Phase I, the research team will study plasma-assisted combustion of methane in air, conduct preliminary research to improve plasma-flame interactions, and investigate influences of new plasma- actuator configurations on flame stability limits. The Phase I studies aim at evaluating key concepts: Bench top evaluation of plasma actuators and combustion chamber concepts will include circuit measurements of power requirements, spectroscopy to establish power coupling into key electronically excited gas species, and gas analysis to monitor combustion efficiency, as well as high-speed imaging and novel flow visualization to gauge mixing effects. Comparisons of plasma excitation methods will be made to develop benchmarks of the new approaches; plasma excitation equipment from previous efforts covering a broad catalog of techniques can be leveraged, e.g., high frequency AC, ns-pulsed, capacitive RF, microwave, and pulser-sustainer hybrids. Plasma discharge arrays, and multi-actuator systems will be devised, aimed at scaling the power input into the combustion flow, and providing stable conditions. Work will focus on demonstrating scaling of arrays of magnetically-driven plasma filaments, driven with compact modules powered from traditional wall-plug sources which can be easily transitioned to commercial products. Phase I analyses will enable design of a robust commercial prototype in Phase II, to support further R&D and commercialization. Potential markets for this technology are high-efficiency gas-turbine engines with improved turn-down ratio, advanced commercial and residential furnaces and boilers, and compact on-demand hybrid (gas-electric) water heaters.