  Plasma Assisted Combustion (PAC) is a promising technology to enhance the
combustion of lean mixtures prone to instabilities and flame blow-off. Although
many PAC experiments demonstrated combustion enhancement, several studies
report an increase in NOx emissions. The aim of this study is to determine the
kinetic pathways leading to NOx formation in the second stage of a sequential
combustor assisted by Nanosecond Repetitively Pulsed Discharges (NRPDs). For
this purpose, Large Eddy Simulation (LES) associated with an accurate
description of the combustion/NOx chemistry and a phenomenological model of the
plasma kinetics is used. Detailed kinetics 0-Dimensional reactors complement
the study. First, the LES setup is validated by comparison with experiments.
Then, the NOx chemistry is analyzed. For the conditions of operation studied,
it is shown that the production of atomic nitrogen in the plasma by direct
electron impact on nitrogen molecules increases the formation of NO. Then, the
NO molecules are transported through the turbulent flame without being strongly
affected. This study illustrates the need to limit the diatomic nitrogen
dissociation process in order to mitigate harmful emissions. More generally,
the very good agreement with experimental measurements demonstrates the
capability of LES combined with accurate models to predict the NRPD effects on
both turbulent combustion and NOx emissions.
