Journal of Atmospheric Chemistry 41: 315–317, 2002. 315

Book Review

Jürgen Warnatz, Ulrich Maas, Robert W. Dibble: Combustion, 3rd edn, Springer-Verlag, Berlin, 2001, x + 299 pp., ISBN 3-540-67751-8, U.S. $49.95.

This book is to provide first-year graduate students with a basic knowledge of com-bustion processes. Since the first edition, which was based on lecture notes of thelead author, the book has undergone several revisions until it reached the presentformat. It now provides a compact yet quite thorough treatment of combustionprocesses. The fact that combustion is an interdisciplinary subject is made clearby the subtitle ‘Physical and Chemical Fundamentals, Modeling and Simulation,Experiments, Pollutant Formation’.

The subject is developed in 18 chapters of which the first two are devoted toa description of basic flame types and the experimental study of flames by meansof optical techniques. The authors emphasize that our current understanding offlame processes is largely based on a comparison of the behavior predicted bymathematical models and that observed in detail in experiments. Chapter 3 lays thefoundation for the mathematical description of the simplest of all flames to treat:the premixed flat laminar flame. Conservation equations, the transport of massand heat, and conditions for establishing a stationary flame front are discussed.The following chapters present additional basic material on the thermodynamics,transport phenomena, chemical kinetics, and reaction mechanisms. Most of thiskind of information can be found in standard textbooks on physical chemistry,but in developing the subject the authors rely specifically on examples taken fromtheir experience with combustion processes. Thus, in treating complex reactionmechanisms, they place much emphasis on criteria that one may use to simplifythe mechanism and to identify the most sensitive of the many reactions occurringin flames. Chapter 8 integrates the material discussed so far by presenting numer-ical techniques to obtain realistic solutions of the system of differential equationsdescribing laminar premixed flames.

A subsequent chapter treats laminar non-premixed flames, that is flames inwhich fuels and oxidizer diffuse to the flame front. As with premixed flames,the underlying principles are simple, yet the inclusion of all the relevant terms inthe conservation equations results in a system of partial differential equations thatcan rarely be solved except by numerical integration. Discussion of the methane-

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air counter-flow non-premixed flame shows that it can be modeled quite well,with experimental data being closely reproduced by the calculations. The fol-lowing chapter on ignition processes treats various aspects of thermal explosions,auto-ignition, spark ignition, minimum ignition energies, and detonations. The dis-cussion is semi-quantitative in view of the difficulties encountered in solving thetime-dependent conservation equation even with the help of fast computers.

The discussion then turns to turbulent flames. One of the consequences of tur-bulence is that the rate of mixing is enhanced compared to laminar flames, yetit remains less even, so that mathematical modeling becomes more complicated.Direct numerical solutions of the Navier-Stokes equations demand a prohibitiveamount of computer time, and simplifications are required that are, in effect, aver-aging procedures. Various approaches are discussed as well as the phenomenon offlame extinction, which occurs at a critical thermal dissipation rate. The next stageof sophistication involves the combustion of liquid and solid fuels. The introductionof a phase boundary makes this subject even more complex than that of turbulentflames, so that it is discussed rather briefly.

The remaining three chapters return to problems of reaction kinetics. Chapter16 treats the phenomenon of engine knock, which is associated with a change inchemical mechanism compared with the normal engine cycle. The formation ofnitrogen oxides is given much room in addition to possible schemes of reducingNOx by the modification of combustion devices. This aspect, which is of consider-able interest to atmospheric chemistry, has been studied extensively during recentyears and the progress achieved is covered in much detail. In the final chapter onhydrocarbon and soot formation it is pointed out that formation of hydrocarbonsand soot precedes that of NOx, and that conditions chosen to avoid soot forma-tion generally lead to larger rates of NOx formation. While the mechanisms ofNOx formation are now reasonably well understood, the level of understandinghydrocarbons and soot formation is still unsatisfactory. The dilemma is that, onthe one hand, combustion can form toxic substances, whereas on the other handcombustion is trusted to destroy toxic substances, medical wastes and municipalsolid waste. Hydrocarbons are formed as intermediates, and they can leave thecombustion chamber as a consequence of local flame extinction. Soot formationproceeds by coagulation of polycyclic aromatic hydrocarbons, PAH, that are gener-ated from smaller hydrocarbon fragments. In this case, the measured and calculatedprofiles of PAH in premixed laminar acetylene flames deviate considerably fromeach other showing that further studies and model improvements are required.

Combustion processes are responsible for much of the air pollution encounteredin populous regions of the world, and for this reason atmospheric chemists shouldhave more than a passing interest in combustion phenomena. This book providesan excellent introduction to the subject with references to many recent researchresults, emphasizing the current level of understanding reached by computer mod-

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eling. A set of exercises completes each chapter. Some of them appear to be rathertime consuming, but in general the questions are designed to train the handling ofequations introduced in the text. About 250 literature citations at the end of thebook, mostly of a recent vintage, provide a source of additional information.

Max Planck Institute für Chemie, PETER WARNECK

55020 Mainz, Germany