Akademik Veri Yönetim Sistemi
Fuel, cilt.426, 2026 (SCI-Expanded, Scopus)
In the transition to sustainable energy systems, ensuring flame stability and controlling pollutant formation remain key challenges. This study investigates the instability behavior and emission characteristics of a 70% H2–30% CH4 mixture under He, N2, and Ar dilution, while providing a physical interpretation of how the thermophysical properties of different diluent gases affect combustion under high swirl and low oxygen conditions. Low-oxygen conditions were achieved by reducing the oxidizer O2 level from 21% to 16% through controlled dilution. Experiments were conducted in a 3 kW high-swirl burner (S = 1.6, φ = 0.7), and thermoacoustic instabilities were quantified via dynamic pressure measurements under external acoustic forcing. Among the diluent gases, He most effectively suppressed thermoacoustic instability, showing the greatest reduction in dynamic pressure oscillation amplitudes, followed by N2, while Ar exhibited the weakest and least monotonic response. Accordingly, the suppression order was He ' N2 ' Ar. Under undiluted conditions, CO and NOX emissions were 91 ppm and 14 ppm, respectively. Increasing dilution led to higher CO levels for all diluents, indicating reduced oxidation efficiency. NOX increased only with N2 dilution due to its limited thermal quenching capability. At 16% O2, CO emissions reached 659 ppm (He), 642 ppm (N2), and a notably lower 401 ppm (Ar), suggesting that Ar provides a more balanced trade-off between dilution and combustion completeness. Flame temperature and luminosity decreased with increasing dilution, most prominently for He due to its high thermal diffusivity. Complementary numerical analyses showed that reducing O2 concentration decreased laminar flame speed for all diluents, with a smaller reduction for He and a more pronounced decrease for N2. In contrast, turbulent flame speed increased with He dilution but decreased with N2 and Ar dilution. The decrease in the Damkohler number indicates that, under low O2 conditions, the reaction–flow balance shifts toward turbulence-dominated flame propagation. Overall, the findings show that differences between diluents cannot be explained solely by oxygen reduction, but also arise from variations in density, thermal diffusivity, and heat capacity under high swirl conditions.