Using a strained flame model to collapse dynamic mode data in a swirl-stabilized syngas combustor

Abstract

The combustion dynamics of carbon monoxide–hydrogen mixtures (syngas) are investigated in an atmospheric pressure swirl-stabilized combustor. Numerical simulations of strained laminar flames are used to determine the consumption speed of syngas mixtures as a function of fuel composition, equivalence ratio and strain rate. Pressure measurements and high-speed video from the experiments are used to identify several distinct operating modes. Across the range of fuel mixtures and equivalence ratios tested, three distinct dynamic regimes are observed. Near the lean blowout limit, stable helical flames anchored within the central recirculation zone are observed. In this regime, the flame appears to wrap around a precessing vortex core. At intermediate equivalence ratios, low-frequency, weakly oscillating quasi-stable flames anchored at the swirler centerbody are observed. At higher equivalence ratios, the flame becomes unstable and oscillates at higher frequencies coupled with the combustor acoustics. The flame under these conditions is impacted by vortex formation in the outer recirculation zone. Higher hydrogen concentration in the fuel reduces the equivalence ratios at which the transitions between regimes are observed. We demonstrate that the numerical results can be used to collapse the gain curves describing the transitions among the three dynamic modes into a function of strained flame speed alone, rather than a function dependent on both equivalence ratio and fuel composition.