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In this paper we explore the effects of nanosecond repetitively pulsed discharges (NRPD) on combustion instabilities and NOx emissions of CH4/NH3 flames, in a swirl-stabilized, 6 kW combustor. The combustor has a large dump plane ratio resulting in a turbulent flame with a single compact macrostructure across all operating conditions. Discharges are setup with a central pin-to-cylindrical-wall type electrode configuration with a discharge gap of 4.55 mm at the dump plane. For pure methane, instabilities occur at various frequencies and amplitudes, up to 1000 Pa. NPRD actuation was successful in suppressing instabilities across all conditions, with best reduction being as much as 23 dB. The discharge voltages ranged from 6-9 kV at a pulse rate of 9 kHz, equivalent to 5-12 mJ/pulse energies and plasma powers less than 99W. For pure CH4 flames, the NRPD actuation increased NOx emissions, but for high NH3/CH4 blends, the NRPD actuation reduced NOx emissions.