Experimental Studies on Lean Blowout Limits for a Hydrogen-Enriched Methane-Fueled Trapped Vortex Combustor

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Abstract In light of stringent emission regulations and environmental considerations, hydrogen is being considered a viable alternative to replace hydrocarbon fuels. However, hydrogen combustion poses challenges regarding NOx emissions, combustion instability, flashback, and blowout limits. The present study aims to investigate the lean blowout of TVC using methane-hydrogen blends with varied hydrogen concentrations. Furthermore, the flame dynamics near lean blowout in the TVC is achieved by reducing the equivalence ratio and studied in detail using high-speed OH*-chemiluminescence (5 kHz), emissions, and temperature measurements. A trapped vortex combustor is considered for the present study because of its numerous advantages: reduced emissions, improved flame stabilization, increased combustion efficiency, exceptional high-altitude re-ignition capabilities, and operating in lean burn or RQL combustion modes. The lean blowout limit is achieved by reducing the equivalence ratio in the cavity inlet until the blowout event occurs, while the equivalence ratio in the main flow is set to zero. The findings reveal significant changes inflame structure as the lean blowout limit is approached. At higher equivalence ratios, the heat release zone is observed to be distributed within the cavity. However, near the lean blowout limit, the heat release zone is confined to the cavity jet shear layer, which is observed to stabilize near the aft wall of the cavity. As the percentage of hydrogen increases, a significant decrease in the lean blowout limit is observed, accompanied by lower hydrocarbon and CO emissions. Thus, the present study demonstrated a broadening of the operating range of the trapped vortex combustor with lower emissions when hydrogen concentration increases.