Numerical study of nitrogen oxides chemistry during plasma assisted combustion in a sequential combustor

TL;DR

This study uses LES simulations to analyze NOx formation pathways in plasma-assisted combustion, highlighting the impact of plasma-induced nitrogen dissociation and demonstrating the model's accuracy in predicting emissions.

Contribution

It introduces a combined LES and phenomenological plasma kinetics model to accurately predict NOx emissions in plasma-assisted combustion.

Findings

Plasma increases atomic nitrogen production, leading to higher NO formation.

NO molecules are transported through the flame with minimal impact from plasma.

Limiting nitrogen dissociation can reduce NOx emissions.

Abstract

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.