Introduction

This book is about unsteady combusting flows, with a particular emphasis on the system dynamics that occur at the intersection of the combustion, fluid mechanics, and acoustic disciplines – that is, on combustor physics. In other words, this is not a combustion book – rather, it treats the interactions of flames with unsteady flow processes that control the behavior of combustor systems. Whereas numerous topics in reactive flow dynamics are “unsteady” (e.g., internal combustion engines, detonations, flame flickering in buoyancy dominated flows, and thermoacoustic instabilities), this text focuses specifically on unsteady combustor issues in high Reynolds number, gas phase, subsonic flows. This book is written for individuals with a background in fluid mechanics and combustion (it does not presuppose a background in acoustics) and is organized to synthesize these fields into a coherent understanding of the intrinsically unsteady processes in combustors.

Unsteady combustor processes define many of the most important considerations associated with modern combustor design. These unsteady processes include transient, time harmonic, and statistically stationary, stochastic processes. For example, ignition, flame blowoff, and flashback are transient combustor issues that often define the range of fuel/air ratios or velocities over which a combustor can operate. As we discuss in this book, these transient processes involve the coupling of chemical kinetics, mass and energy transport, flame propagation in high shear flow regions, hydrodynamic flow stability, and interaction of flame-induced dilatation on the flow field – much more than a simple balance of flame speed and flow velocity.