Influence of nitrogen contents in fuel and oxidizer on nitrogen oxide emissions during NG/O2 combustion

Abstract

This study aims to understand the NOx emission characteristics during pure oxygen (O2) combustion of natural gas (NG) and to provide design data for application in forging furnaces. We numerically investigated the sensitivity of NOx emissions to an up to 10 % increase in nitrogen (N2) content of the fuel and oxidizer. According to the impact analysis, the two cases have a more adverse effect on NOx emissions. The numerical model established in this study was verified using experimental results obtained by the International Flame Research Foundation (IFRF). In addition, the N2 content of the fuel was fixed and the impact of NOx emissions on the O2 ratio (O2/fuel equivalence ratio) was investigated. The calculated results for the temperature field, velocity field, and NOx concentration at the furnace outlet agree with the IFRF experimental results. As the N2 content in the oxidizer and fuel increased, the NOx concentration also increased. NOx emissions were much higher with a larger amount of N2 in the fuel than in the oxidizer. With fixed N2 content in the fuel, NOx concentration tended to increase as the O2 ratio increased. As the N2 content in the fuel increased, the tendency of the NOx concentration to increase with the O2 ratio became more evident. This study emphasizes the importance of minimizing the N2 content in both the fuel and oxidizer during NG-O2 combustion, and suggests that NOx emissions can be effectively controlled by adjusting the oxygen ratio when N2 is present. © 2025 The Authors