Numerical Analysis of Thermal Intensity and NOx Mitigation in Oxy-Methane Combustion: The Strategic Role of CO2 Dilution for CCS Integration

Nur Atiqah Habib; Nor Afzanizam Samiran; Izuan Amin Ishak; Rais Hanizam Madon; Nik Normunira Mat Hassan

doi:10.37934/sej.14.1.1836

Authors

Nur Atiqah Habib Department of Mechanical Engineering Technology, Faculty of Engineering Technology, Universiti Tun Hussein Onn Malaysia (UTHM) Higher Education Hub Pagoh, KM 1, Jalan Panchor, 84600 Panchor, Johor, Malaysia
Nor Afzanizam Samiran Department of Mechanical Engineering Technology, Faculty of Engineering Technology, Universiti Tun Hussein Onn Malaysia (UTHM) Higher Education Hub Pagoh, KM 1, Jalan Panchor, 84600 Panchor, Johor, Malaysia
Izuan Amin Ishak Department of Mechanical Engineering Technology, Faculty of Engineering Technology, Universiti Tun Hussein Onn Malaysia (UTHM) Higher Education Hub Pagoh, KM 1, Jalan Panchor, 84600 Panchor, Johor, Malaysia
Rais Hanizam Madon Department of Mechanical Technology, Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia (UTHM), 86400 Parit Raja, Batu Pahat, Johor, Malaysia
Nik Normunira Mat Hassan Faculty of Mechanical Engineering, Kompleks Kejuruteraan Tuanku Abdul Halim Mu'adzam Shah, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia

DOI:

https://doi.org/10.37934/sej.14.1.1836

Keywords:

Oxy-methane combustion, CFD, NOx emissions, Velocity distribution, CO2 dilution, Carbon Capture and Storage (CCS)

Abstract

The transition towards oxy–methane combustion is mainly driven by the need to improve CO₂ separation for carbon capture and storage (CCS) applications. However, operating with pure oxygen without any form of dilution often results in excessively high flame temperatures, which can significantly promote thermal NOₓ formation. In this study, the issue is examined through CFD simulations, focusing on both emission characteristics and thermal behaviour. The modelling framework combines the k–ω SST turbulence model with a mixture fraction PDF approach to compare three combustion environments, namely air combustion, pure oxygen, and a 50% O₂– 50% CO₂ oxy-fuel mixture. The numerical model was first validated against reference data, with temperature deviations remaining below 10%, indicating reasonable agreement. The results show that the pure oxygen case produces the highest peak temperature, reaching approximately 1900 K, which is accompanied by a significant increase in NO emissions due to the temperature-sensitive Zeldovich mechanism. When CO₂ is introduced as a diluent, the combustion behaviour changes noticeably. The peak temperature decreases to around 1600 K, while NO formation is reduced. This can be linked to the higher heat capacity of CO₂ as well as its contribution to radiative heat transfer, both of which help to moderate the combustion process. Further analysis of the velocity field and species distribution (CO, O₂, CO₂, and N₂) suggests that the 50% O₂– 50% CO₂ configuration provides a more balanced condition. It maintains flame stability while keeping pollutant emissions at a lower level and, at the same time, produces a CO₂-rich exhaust stream that is more suitable for CCS applications. Overall, the findings suggest that CO₂ dilution plays a key role in achieving a practical balance between combustion performance, emission control, and sustainability. This highlights its importance in the design of future low-carbon combustion systems.