Thermal and chemical effects induced by NRP glow discharges applied to an ammonia-hydrogen-air flame

Nanosecond repetitively pulsed (NRP) glow discharges have shown promising enhancement capabilities for ammonia combustion. However, optimizing a plasma assisted ammonia combustion strategy is currently challenging due to uncertainties in chemical kinetic mechanisms. In this work, we investigate the thermal and kinetic effects induced by nanosecond repetitively pulsed (NRP) glow discharges applied across a stationary, laminar, and axis-symmetric ammonia-hydrogen-air flame employing optical emission spectroscopy and laser induced fluorescence. The plasma is shown to induce fast heating of up to 380 K within 14 ns from the start of a discharge but this heating was localized around the anode tip. Slow heating upstream of the flame by 120-230 K is shown to be induced by the plasma. NH and NH2 imaging show that these two species are produced by the plasma during and after the discharge illustrating the chemical activation by the plasma during and after the discharge. The imaging also show that the plasma dissociate less than 10% of ammonia upstream if the flame. This indicate that the plasma produced NH and NH2 have mole fractions less than 18,500 ppm. The cumulative dissociation of ammonia from the nozzle to the flame front is insignificant compared to the dissociation of ammonia in the preheat zone of the flame. These results highlights various thermal and kinetic effects that the plasma induces while enhancing ammonia flames.