Synergistic effect of non-thermal plasma and CH₄ addition on turbulent NH₃/air premixed flames in a swirl combustor

The synergistic effect of non-thermal plasma (NTP) induced by a dielectric barrier discharge (DBD) and CH4 addition on turbulent swirl-stabilized NH3/air premixed flames in a laboratory-scale gas turbine combustor is experimentally investigated by varying the mixture equivalence ratio, phi, the mixt velocity, U-0, and the mole fraction of CH4 in the fuel, X-f,X-CH4. It is found that the streamer intensity is significantly increased by adding CH4 to NH3/air flames compared with that by adding H-2. This is because positive ions generated by CH4 addition play a critical role in generating streamers. Such streamers intensified by CH4 addition enhance the ammonia combustion more together with CH4, and hence, the lean blowout (LBO) limits of NH3/CH4/air flames are significantly extended compared with those without applying NTP. The maximum streamer intensity is found to be linearly proportional to phi, X-f,X-CH4 in wide ranges of phi, X-f,X-CH4, and U-0. NTP is also found to significantly reduce the amount of NOx and CO emissions simultaneously. All of the results suggest that NTP can be used more effectively with CH4 addition to stabilize turbulent premixed NH3/air flames and reduce NOx/CO emissions, which is attributed to their synergistic effect on the ammonia combustion.