Enhancement of lean blowout limits of swirl stabilized NH3-CH4-Air flames using nanosecond repetitively pulsed discharges at elevated pressures

This study experimentally examines the impact of nanosecond repetitively pulsed (NRP) discharges on lean premixed methane-ammonia-air swirl flames at pressures up to 4 bar. The results reveal the extension of flame blowout limit by 10-12 % under atmospheric conditions and 5-6 % at 4 bar, when NRP discharges are applied. This decrease in the plasma effect could be attributed to the detrimental impact of strong shock waves at high pressure, destabilizing the flame. NH3-CH4-air flames shows higher lean blowout limits in comparison to CH4-air flames. NRP discharges exhibit consistent impact on the lean blowout limit enhancement across ammonia fractions (20-60 %), irrespective of pressure conditions. These results are obtained for a ratio of NRP discharge power to flame thermal power of 0.63 % and constant pulse repetition frequency of 30 kHz.