Hydrocarbon Flame Speed Enhancement with High-Power Pulsed Microwaves

Recent developments have been made in the investigation of a pulsed microwave enhanced combustion system that demonstrates a significant increase in the laminar flame speed of a CH4/air stagnation flame. Previous research has quantified a 20%-25% flame speed enhancement with a 1.3 kW continuous wave (CW) microwave system and new, pulsed magnetron radiation results qualitatively show a similar level of increase with 50 times less power. This apparent ability to actively control hydrocarbon flame speed may prove to be a viable tool for issues that plague hypersonic combustors. The significance of the move towards a pulsed microwave system is two-fold. For one, the question of coupling efficiency is slightly alleviated with the 25 W average power, 1000 Hz repetition rate (0.001 duty cycle) pulses. Secondly the short-pulsed microwave system has proven to not create the parasitic breakdown effect that was seen with high levels of CW-radiation. In fact, even with generation of a pulsed plasma in the post-flame region, the enhancement remains and at this point qualitatively appears to be of a greater magnitude than that seen with the CW system.

Overview