Scaling of Stability Limits in Lean-Premixed Gas Turbine Combustors

Abstract

The prediction and the systematic suppression of self-sustained combustion instabilities in combustors for gas turbine applications still suffer from incomplete physical understanding of the feedback mechanisms and lack of experimental data of the dynamic flame characteristics of Lean-Premixed swirl flames. Hence, the experimental determination of the flame transfer functions of LP swirl flames was achieved using a mixing unit to generate a time-independent and spatial homogeneous mixture of natural gas and combustion air at the burner exit. The determined LP flame dynamics are strongly affected by the formation and in-phase reaction of coherent vortex structures, well known as drivers of combustion instabilities, that have been visualized with an phase-correlated imaging technique. The results discussed in this paper lead to a basic understanding of the frequency-dependent dynamics of LP swirl flames on periodic disturbances and especially, of the influence of the preheating temperature and the air equivalence ratio on the amplitude responses and phase angle functions. Based on the measurements and theoretical considerations concerning the burning velocity of steady-state premixed flames a physical model and — derived from it — scaling laws for the prediction of unstable operation modes in dependence of main operation parameters of the flame were formulated and validated by measurements.