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Abstract
Measurements are described in which the effect of intense microwave fields (≃2 × 105 V/m) upon flame velocities in acetylene-air, ethylene-air and propane-air mixtures was determined. The measurements extend those reported in a previous paper in which no enhancement of velocity was observed with the application of miciowave radiation (<2x 104 V/m). The more intense fields were capable of producing gas breakdown behind the flame front and for these circumstances flame speed enhancement of up to ∼40 percent was observed. However when gas breakdown did not occur a smaller (<20 percent for ethylene, <10 percent for propane and acetylene flames) enhancement was observed. Also, it was only for very lean mixtures that there was flame speed enhancement; the maximum enhancement occurring just slightly rich of the lean limit. Because the large flame velocity enhancement was observed only when gas breakdown took place and as such a large amount of rf power was delivered to the flame, the application of this effect to augment flame speed in a practical situation is not encouraging.