Chapter List

I. Introduction

COMBUSTION instability has become a major issue for gas turbine manufacturers. Stricter emission regulations, in particular, on nitrogen oxides, have led to the development of new combustion methods such as lean premixed, prevaporized (LPP) combustion to replace the traditional diffusion flame. However, LPP combustion is much more liable to generate strong oscillations that can damage equipment and limit operating conditions. In this chapter, methods to investigate combustion instabilities are reviewed (see also Dowling and Stow1). The emphasis is on gas-turbine applications and LPP combustion. The flow is modeled as a one-dimensional mean with linear perturbations. Calculations are typically done in the frequency domain. The techniques described lead to predictions for the frequencies of oscillations and the susceptibility to instabilities in which linear disturbances grow exponentially in time. Appropriate boundary conditions are discussed, as is the change in the linearized flow across zones of heat addition and/or area change. Many of the key concepts are first introduced by considering one-dimensional perturbations. Later, higher-order modes, in particular, circumferential waves, are introduced and modal coupling is discussed. The modeling of...