11. Syngas Combustion Dynamics in a Bluff-Body Turbulent Combustor

Future energy needs that are supplemented by combustion require alternate fuel sources derived from both fossil and non-fossil sources. In this regard, syngas provides a relatively clean and large-scale resource. However, contrasted to conventional gaseous fuels, syngas poses challenges along both static and dynamic stability of flames owing to source dependent composition changes. These often result in altered global flame stabilization and dynamics when compared to its constituents being individually combusted. The present chapter deals with dynamic challenges is syngas combustion, when its static component, i.e., flame stabilization, is taken to be sufficiently addressed by resorting to non-premixed combustion. The chapter is descriptive of the combustion dynamics of syngas combustion across varying compositions in a turbulent bluff-body combustor, with focus on numerous aspects that need to be accounted to explain the vastly different behavior that syngas combustion dynamics display. The differences in the dynamic behavior of syngas compared to fuels that have been sought to “mimic” syngas like hydrogen-enriched hydrocarbon include-1. Excitation of higher modes across similar parameter change and most significantly 2. Presence of two heat release rate zones as a result of differing diffusion and chemical time-scales. Time-resolved pressure, velocity and OH* and CO₂* imaging reveal that peculiarities arising in syngas combustion dynamics are a result of various steady and unsteady processes viz. fuel to air momentum ratio, the effect of the same on mean flame stabilization, baroclinic torque, shear layer stabilization and the offset between peak OH* and CO₂* concentrations. The foresaid processes are aided by the time-lag between acoustic quantities that result in excitation of various modes as seen from a simple theoretical model. The chapter thus explains the unique nature of syngas combustion from a multitude of well-established combustion theories that are required to understand and control the dynamic challenges of syngas combustion.