Chemiluminescence and emission characteristics of hydrogen enriched methane inverse diffusion flame in a multi-slit rectangular burner

In the transition toward low-carbon energy systems, blending hydrogen into existing natural gas infrastructure presents both opportunities and challenges for domestic combustion technologies. In this context, inverse diffusion flames (IDFs), which offer broad stability ranges and low pollutant emissions, are promising candidates for such applications. Hence, this study investigates the effects of enrichment on flame structure, chemiluminescence response and flue gas emissions in methane based IDFs stabilized on a multi-slit rectangular burner. To this end, high-resolution imaging, spatially resolved chemiluminescence spectroscopy of and radicals and flue gas analysis were employed. Experiments were conducted using - fuel mixtures with 0 % , 25 % and 50% (v/v), under globally fuel-lean conditions at constant thermal power of W. Results revealed two distinct flame regimes: anchored/stable (Type I) and a lifted/unstable (Type II), with addition extending the stability of Type I flames toward lower equivalence ratios. Spectroscopic analysis revealed consistent spatial overlap between and emissions, with intensity reductions due to faster kinetics and carbon dilution with increasing content. The ratio remained relatively stable across enrichment levels, suggesting preserved local equivalence ratio distribution. Emission results showed that in Type I flames, and were consistently low, while decreased proportionally with carbon content. formation was dominated by the prompt-NO mechanism and decreased with addition due to reduced availability. These findings highlight the potential of enrichment in stabilizing multi-slit IDF combustion systems at ultra-lean conditions, while reducing carbon-based and emissions. • H 2 extends inverse diffusion flame stability toward lower global equivalence ratios. • OH*/CH* kept unchanged, indicating preserved local equivalence ratio distribution. • CH* and OH* trace flame envelope and reveal inner zone sensitivity to H 2 . • Low CO and unburned hydrocarbon levels observed, while CO 2 drops with H 2 enrichment. • NOx is dominated by prompt-NO mechanism and H 2 reduces emissions by CH* suppression.