Impact of K-H Instability on NOx Emissions in N2O Thermal Decomposition Using Premixed CH4 Co-Flow Flames and Electric Furnace

Abstract

This study systematically investigates the formation of NOx in the thermal decomposition of N2O, focusing on the impact of Kelvin–Helmholtz (K-H) instability in combustion environments. Using premixed CH4 co-flow flames and an electric furnace as distinct heat sources, we explored NOx emission dynamics under varying conditions, including reaction temperature, residence time, and N2O dilution rates (XN2O). Our findings demonstrate that diluting N2O around a premixed flame increases flame length and decreases flame propagation velocity, inducing K-H instability. This instability was quantitatively characterized using Richardson and Strouhal numbers, highlighting N2O’s role in augmenting oxygen supply within the flame and significantly altering flame dynamics. The study reveals that higher XN2O consistently led to increased NO formation independently of nozzle exit velocity (ujet) or co-flow rate, emphasizing the influence of N2O concentration on NO production. In scenarios without K-H instability, particularly at lower ujet, an exponential rise in NO2 formation rates was observed, due to the reduced residence time of N2O near the flame surface, limiting pyrolysis effectiveness. Conversely, at higher ujet where K-H instability occurs, the formation rate of NO2 drastically decreased. This suggests that K-H instability is crucial in optimizing N2O decomposition for minimal NOx production.