Advanced numerical study of two-stage methane oxidation in axisymmetric turbulent flows

Abstract

This study explores crucial efforts to reduce harmful emissions such as carbon dioxide CO2, toxic carbon monoxide CO, and nitrogen oxides NOx in industrial plants, gas turbines, and thermal power systems, especially as global environmental standards grow stricter. Traditional single-stage combustion models often fall short in capturing intermediate product dynamics and temperature gradients. To address these issues, the study introduces an advanced numerical method to simulate the propagation and combustion of an axisymmetric methane jet within an infinite co-flowing air stream, based on a two-stage oxidation mechanism. The model employs a system of dimensionless differential equations for a turbulent boundary layer of reacting multi-component gases in Mises coordinates. A two-parameter turbulence model is used to accurately capture turbulence effects and mixing. Additionally, to manage the complexity of multi-component, two-stage chemical reactions, Shvab-Zeldovich relative excess functions are incorporated into the continuity and diffusion equations, simplifying the system to three main equations. For numerical solutions in Mises variables, a two-layer, six-point implicit finite-difference scheme with second-order accuracy is developed. An iterative process is also implemented to ensure numerical stability amidst strong nonlinearities in conservation laws and substance transport equations. The results—highlighting two-stage combustion dynamics, temperature and velocity fields, and thermogasdynamic features—provide a solid theoretical basis for optimizing engineering design and creating environmentally friendly, energy-efficient combustion chambers.