Oxygen enrichment studies in hydrogen-natural gas burner: A pilot-scale study on emissions and thermal performance

Decarbonising high-temperature industrial furnaces requires efficient and low-emission combustion strategies. Hydrogen and oxygen enhanced combustion (OEC) are promising alternatives to conventional air-fuel systems, but their combined impact on heat transfer, efficiency, and NOx emissions under practical operating conditions remains underexplored. This study explores the combustion behaviour of a commercial 200 kW burner operating with hydrogen, natural gas, and their blend under varying oxidizer oxygen concentrations, ranging from air-fuel combustion (21% O 2 ) to pure oxyfuel combustion (100% O 2 ). Conducted at pilot-scale, the research aims to understand how fuel composition and oxygen enrichment influence NOx emissions, heat transfer, wall temperature distribution, and flue gas energy losses. The results reveal that oxygen enrichment plays a dominant role in shaping combustion performance, while the choice of fuel (whether hydrogen, natural gas, or a blend) has a comparatively minor effect. Oxygen enrichment significantly improved heat transfer and reduced flue gas losses, resulting in thermal efficiency increase from ∼45% in air-fuel to ∼80% in oxyfuel combustion. Burner configuration such as delayed combustion and flameless combustion strongly influenced temperature uniformity and NOx emissions, where flameless configuration resulted in enhanced mixing, reduced thermal stratification and lower NOx compared to simple delayed combustion. Under delayed and flameless oxyfuel conditions, NOx emissions dropped below 2 mg/MJ for both fuels. With this study, a reduction of ∼90% in NOx emission while moving from air-fuel to oxyfuel condition was observed for natural gas and hydrogen. Interestingly, at flameless combustion operation, hydrogen showed lower NOx emission than natural gas. Constant-temperature studies confirmed that nitrogen availability, rather than flame temperature, dominated NOx formation under flameless conditions. These findings highlight the potential of oxyfuel and OEC to deliver cleaner and more energy-efficient operation in industrial furnaces, regardless of fuel composition. The insights gained are particularly relevant for industries transitioning toward hydrogen-based energy systems and seeking to meet decarbonisation, NOx emission and efficiency targets.