Numerical modeling of plasma assisted pyrolysis and combustion of ammonia

This work aims at studying the combustion and pyrolysis characteristics of ammonia (NH₃ ) using non-equilibrium plasma. The well known challenges of ammonia combustion and the advantages of using non-equilibrium plasma are discussed using results of zero-dimensional and one-dimensional coupled simulations. Periodic nanosecond pulsed discharges of plasma are interspersed with microsecond gaps of combustion to assess the assistance provided by plasma on overall combustion characteristics of ammonia fuel, such as ignition delay and flammability limit. Due to the lack of a reliable plasma mechanism for ammonia, a validated plasma kinetic mechanism of methane and oxygen is transformed to that of ammonia and oxygen, and is coupled with an experimentally validated ammonia combustion mechanism in this work. Another NH₃ / O₂ / He plasma mechanism that was recently assembled and published is also used to study the discharge and inter-pulse kinetics. A 0D model is developed to compute the rates of the electron impact reactions during the discharge, and ion-electron recombination reactions and quenching reactions along with the combustion reactions during the gap. Finally, the species concentrations and temperatures from this model are compared with those obtained using a detailed 1D model which solves for the transient electric field in addition to the species concentrations and temperature.