Autoignition of methane and methane/hydrogen blends in CO2 bath gas

•Advancement of direct-fired supercritical CO2 (sCO2) combustion cycles.•Insightful CH4/H2 blend ignition delay data in CO2 rich environments.•CO2 dilution effects for CH4/H2 blend in shock tubes.•Cleaner and efficient combustion technologies in CO2-enriched environments. Combustion in large dilutions of carbon dioxide (CO2) has the potential to enable fossil fuel combustion with 100 % inherent carbon capture by simplifying the post-combustion carbon capture process into the facile separation of CO2 and water. Emerging technologies that employ CO2 as a bath gas, exemplified by the Allam-Fetvedt cycle, are gaining widespread international attention, evidenced by ongoing plant developments in both the United Kingdom and the United States. This study presents new ignition delay time datasets (IDTs) for the combustion of methane and methane/hydrogen blends at 20 and 40 bar. The chemical kinetics governing these distinct conditions are investigated by utilizing two distinct chemical kinetic mechanisms, namely UoS sCO2 2.0 and NUIGMech1.1. Ignition delay datasets of methane/hydrogen blends are presented alongside a detailed discussion of the effect CO2, in contrast to N2, on the combustion mechanism. The differences in kinetics of pure methane and pure hydrogen are also discussed with regards to key reactions and the radical pool. This study aims to elucidate the intricate interplay of factors shaping ignition dynamics in CO2– enriched environments.