Analysis of Injector Staging Patterns With Comparisons of Limit Cycle Amplitudes Over a Full Domain of Operation

Abstract

Injector staging has recently been demonstrated to control thermoacoustic instabilities in an annular combustor, but its effects were investigated at a single operating point. This work extends this concept to a wide operating domain comprising a range of thermal powers and equivalence ratios. Staging consists in mixing two types of injectors, each exhibiting distinct flame responses when operated individually. Experiments carried out on the laboratory scale annular combustor MICCA map the instability region for several staging patterns and indicate that they affect the instability layout and the limit-cycle amplitude within it.

A reduced-order model is applied to the same operating domain and staging configurations. The model, expressed in slow-flow variables, captures the envelope of modal growth and saturation. Time averaging removes fast oscillations, leaving a set of state-dependent delay differential equations governing the nonlinear combustion dynamics. Combined with flame describing functions measured in a single injector combustor, the framework predicts limit-cycle amplitudes, spin ratios, and nodal line angles, which characterize the modal structures of instabilities.

Model predictions are compared with measurements across all conditions, reproducing the overall instability trends, distinguishing stable from unstable conditions, and providing reasonable agreement with limit-cycle levels, frequency and mode structure across the tested staging arrangements.