Kinetics of low temperature plasma assisted NH3/H2 oxidation in a nanosecond-pulsed discharge

Ammonia (NH) has been widely recognized as one of the carbon-neutral fuels. However, ammonia combustion suffers low reactivity and high NO/NO emissions. To overcome these issues, this work reports plasma assisted NH/H oxidation and unveils the kinetics of fuel oxidation and NO/NO formation by combining time-resolved laser diagnostics with plasma modeling. Firstly, we found that the NH consumption is promoted with a H blending ratio of 0.3, due to enhancements of H and OH formation by plasma assisted H dissociation. Secondly, at a high reduced electric field, when the H blending ratio increases, the NH oxidation is promoted due to both the HO formation and strong NO kinetic enhancement via NO-HO and NO-H pathways. In the meantime, it is shown that the NO mole fraction also increases with H blending ratio, because the NO formation is enhanced via N(D)-O pathways, and the DeNO chemistry is weakened with less NH production. By contrast, at a lower reduced electric field, when the H blending ratio increases, the decreased N(D) formation does not produce enough NO to replenish the NO formation drop caused by lower NH concentration. Thirdly, the reduced electric field non-monotonically affects fuel consumption and NO/NO formation by manipulating electron energy deposition pathways. The NH consumption is maximized with an optimal reduced electric field where N* excitation and O dissociation are most efficient. When the reduced electric field deviates from its optimum, the NH consumption decreases due to the discharge energy deposition to either vibrational excitation or dissociation of N. The NO/NO emissions governed by the NH oxidation follow the above NH consumption trend.