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Interpreting chemiluminescence signals and ratios in hydrogenated biogas flames in a micro gas turbine combustor

par Salah, Mohamed salah eddine;Mustafa Kamal, Mustafa;Tarabet, Lyes;Parente, Alessandro
Référence Fuel, 417, 138552
Publication Publié, 2026-07-01

Article révisé par les pairs

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Résumé :

Biogas is a renewable and infrastructure-compatible fuel for distributed power generation, but its high CO2 content lowers heating value and flame speed, complicating flame stabilization and narrowing the flammability range. Hydrogen enrichment widens this range, accelerates ignition, and promotes full oxidation, enabling efficient, low-CO operation. This experimental study investigates hydrogen-enriched biogas combustion in a stagnation-point reverse-flow (SPRF) combustor, a practical configuration featuring internal flue gas recirculation (iFGR). Experiments were performed at 18 kW thermal power under various operating conditions in terms of biogas composition (0–40% CO2 by v/v.), hydrogen fraction (0–50% by v/v.), air-inlet diameters (40 and 24 mm), air preheating (500–900 K), and equivalence ratio (0.4–0.6). The dataset comprises 108 test cases combining dual-camera, two-line imaging of OH*, CH*, C2*, and broadband CO2* (100 Hz) with exhaust CO/NO measurements. Results show that OH* intensity increases monotonically with H2 and serves as a robust tracer of reactivity, while CH* and C2* exhibit non-monotonic behaviour due to competing thermal and carbon-depletion effects. The OH*/CH* and OH*/ C2* ratios track H2 enrichment in the wider-inlet geometry, whereas enhanced mixing in the compact inlet compresses their dynamic range. Comparison with published premixed and diffusion flame studies indicates that OH* intensity and the OH*/CH* ratio exhibit consistent trends, whereas other chemiluminescence signals and ratios are strongly configuration-dependent and require validation for each specific combustor geometry. Flame hysteresis occurs between attached and detached modes: the attached regime yields higher CO and NO due to incomplete oxidation, while the detached regime achieves low-CO operation through intensified air–fuel–recirculation interactions. Finally, Gaussian Process Regression (GPR) models trained on chemiluminescence intensities accurately predict emissions, illustrating the potential of virtual sensing for hydrogen-biogas combustors.