Distributed combustion was investigated with hydrogen-enriched methane fuel in a swirl-stabilized burner. Distributed reaction zones were established from conventional swirl flames at two heat release intensities of 5.72 and 7.63 MW/m3-atm by diluting the main airstream with carbon dioxide. The appearance of distributed reaction zones with hydrogen addition to methane fuel was investigated here. High-speed chemiluminescence imaging was performed for different cases without any spectral filtering to visualize the shape of reaction zones. A gradual increase of % H2 in the fuel mixture increased the chemiluminescence intensity and reduced the flame standoff distance gradually in both the swirl and distributed combustion cases. The reaction zone at higher thermal intensities was found to be wider than the lower thermal intensity case. Distributed reaction zones possessed lower visible chemiluminescence signatures than that of the conventional swirl flames considered. The increased flame chemiluminescence signatures with hydrogen enrichment were related to higher flame reactivity because of hydrogen addition. This hypothesis was verified by computing the laminar flame speed at various hydrogen-enriched cases at different O2 concentrations. The results revealed that the flame speed gradually decreased when the flame transitioned from swirl combustion to distributed combustion regime. Additionally, higher flame speed was observed at different O2 levels corresponding to higher hydrogen content in the fuel mixture.

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