Influence of N2 and CO2 dilution on methane MILD combustion: Insights into temperature distribution and emission optimization

Abstract

This study investigates the effects of various diluents and their proportions on methane-based Moderate or Intense Low-oxygen Dilution (MILD) combustion in a swirl combustion chamber. The experimental analysis focuses on the modulation of the diluent effect by equivalence ratio and thermal power. Key parameters, including temperature distribution, temperature fluctuation rates, and CO and NO emissions, are systematically examined under different operating conditions. The findings demonstrate that CO₂ dilution significantly lowers the combustion temperature, enhances temperature uniformity, and minimizes NO emissions (up to 70%), but increases CO emissions. However, N₂ dilution slightly increases the temperature and reduces CO emissions, with comparatively less effect on NO emissions. Furthermore, variations in equivalence ratio and thermal power have marked effects on temperature and emissions behavior. Appropriate adjustments of these parameters can optimize temperature uniformity and emissions control. This work confirms that optimized MILD combustion can be achieved in a swirl combustion chamber by using CO₂ and N₂ to dilute CH₄, which is a critical insight for advancing the practical application of MILD combustion technology.