Nonlinear mode triggering in a multiple flame combustor

Abstract

A nonlinear analysis of combustion instability is carried out by making use of the Flame Describing Function (FDF) framework. Predictions are compared with data obtained from experiments on a multipoint injection combustor. The burner comprises a premixer manifold of variable length, an injection system and a flame tube. This device features several types of self-sustained oscillation and its dynamics is characterized by nonlinearities like transient frequency shifting, mode switching, mode triggering and hysteresis phenomena which cannot be anticipated from a classical linear stability analysis. It is shown that many of these phenomena can be suitably predicted by including the amplitude dependent response of the flame in a matrix analysis of the system dynamics. More specifically, the present work centers on processes which cannot be anticipated from linear analysis such as mode switching linked to a triggering by the nonlinear flame response.