A Fundamental Investigation of Premixed Hydrogen Oxy-combustion in Carbon Dioxide

Abstract

Hydrogen (H₂) is increasingly viewed as an attractive carbon-free fuel due to its potential compatibility with the existing transportation and conversion infrastructure. However, one of the major challenges facing large-scale deployment is the fundamentally different combustion properties it has in comparison to commonplace hydrocarbon fuels such as natural gas. For example, the laminar burning velocity (LBV) of a combustible mixture has a direct impact on how it can be used in internal combustion engine or gas turbines; the LBV of hydrogen is over 7 times greater than that of natural gas when combusted in air. Carbon dioxide (CO₂) can be used as a working fluid, as opposed to nitrogen (in air), to reduce the flame speed of hydrogen combustion. A mixture of hydrogen, oxygen, and carbon dioxide as a working fluid can provide LBVs comparable to natural gas in air, which potentially enables existing conversion architectures. Furthermore, by replacing nitrogen (N₂) with CO₂ in the mixture, NOx emissions are avoided and opportunities for carbon sequestration or closed-cycle processes are possible. This study experimentally explores fundamental premixed oxy-combustion properties of H₂/CO₂ mixtures in a constant volume combustion chamber (CVCC) across a range of initial pressures (1, 1.5 and 2 bar) and equivalence ratios (0.4, 0.6, 0.8, 1). The spherically expanding flames are examined to determine the flame speed, LBV, and lower flammability limits (LFL) with respect to different CO₂ concentrations (40%, 60%, 65%). Furthermore, it was identified that the flame speed of the 65% CO₂ case at an equivalence ratio of 1 and initial pressure of 1 bar matches the closest with methane-air stoichiometric combustion.