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Unsteady Combustor Physics, by Tim C. Lieuwen

Newcomers and experienced researchers to the field of combustion instabilities will welcome this new tome on Unsteady Combustor Physics. This primer is both a comprehensive review and a solid introduction to the topic, starting from the fundamental equations for reacting systems, acoustics, flow instabilities, and their interaction with combustion heat release. The theme of unsteady combustion is vast, yet the author manages to address each subtopic in a concise way, illustrated by many examples and stepwise explanation of the more difficult arguments. Most chapters contain a series of suggested exercises, mostly consisting of derivations, which are appropriate for the level of the book. Although there are several introductory texts to thermoacoustics and combustion elsewhere, graduate students and researchers will be pleased to find a cohesive account of the principles and advances in the field in one volume. Chapters 1 and 2 lay out the mean and perturbed conservation equations for mass, momentum, and energy, providing a useful quick reference to the fundamental equations used in the field. The physics of the coupling between the various modes of interaction between perturbations is introduced in a clear manner, and the various ways of decomposing the flow via expansions are concisely dealt with, with derivations left to the reader. An introduction to flow systems as dynamical systems provides a handle for understanding limit cycles in instability. Chapters 3 and 4 lay out the framework for understanding instability from the point of view of hydrodynamics, including classical stability analysis of simple flows, as well as a range of examples pertinent to combustion. As a perhaps minor issue, I found the notation and the typesetting rather hard to read throughout the book, for example in the choice of vector overlines rather than bold face, the choice of calligraphic letters, which cannot be easily deciphered, or the choice of MW rather than simply W for molecular weight. Chapter 5 brings in acoustic equations and analytical methods of solution of resonant modes in cavities and annuli. This analytical approach carries onto the following chapter, where the role of coupling of the heat release rate appears, with suggested decomposition approaches for the solution of one-dimensional problems, again illustrated by a number of experimental examples. Here, I would have liked to see a nod to network models and a matrix formulation of state variables, which are widespread in the solution of 1D thermoacoustics problems, as these serve as a practical route to the solution of problems that must be attacked numerically. The following Chapters 6–9 in the book address a range of topics not directly related to combustion instabilities, but to the more general title of the book on unsteady combustion physics. Starting with the kinematics of flame-flow interactions, ignition, and autoignition,