Pulsed Microwave Enhancement of Laminar and Turbulent Hydrocarbon Flames

Further progress on microwave enhanced combustion has been made with the use of high peak-power, short pulse radiation. This research was undertaken to extend the previously demonstrated laminar flame speed microwave enhancement into the turbulent regime. Flame front visualization shows that cw microwave radiation generates a small but measurable enhancement of a Bunsen-type turbulent flame. To avoid the parasitic breakdown that is expected to occur with more powerful cw magnetrons, the use of a pulsed microwave system was explored. Initial experiments with a 25 W average power, 0.1 % duty cycle pulsed magnetron and a laminar burner have demonstrated laminar flame speed enhancements on par with those generated by 1.2 kW cw radiation. In addition, the pulsed microwave source has shown the ability to generate a strong, audible acoustic perturbation in the laminar flame. Filtered Rayleigh scattering (FRS) thermometry measurements have shown no significant preheating of the reactants or bulk heating of the burned gases; a result that may imply microwave radiation is enhancing chemical reaction rates rather than heating the flame zone.

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