Jet Engines - Fundamentals of Theory, Design and Operation

This book is one for those of us with more than a passing interest in jet engines. I find it fascinating that such a simple basic concept has been developed with incredible technical skill into modern jet engines powering a huge range of aircraft from military fighters, through small personal business jets like the Embraer Phenom 100, to the world's largest airliner, the Airbus A380.

The book, written by senior Airbus aerodynamicist Klaus Hunecke, explains the basic principles behind jet engines and how they have been developed for military and civilian applications, including integration with the airframe and environmental considerations.

Originally published in Germany in 1987, the English edition was published in 1997. Despite being now a relatively old publication the information is still correct - aerodynamic principles don't change! Obviously the examples used to illustrate points are not of the most modern engines, but this provides an interesting historical perspective and there have been relatively few "step-change" technological developments since the book was printed.

The first chapter gives a brief history of the invention of the jet engine then describes the different types of engine - turbojet, turboprop, turbofan and turboshaft - with their historic and current applications. The second chapter discusses some fundamental physical principles including basic fluid dynamics and gas laws. Subsequent chapters concentrate on each section of the engine in turn.

Chapter 3 focuses on air intakes. Who would have thought that so much thought goes into the design of an engine intake? Subsonic intake design is complicated enough, but intakes for supersonic aircraft are far more detailed, requiring variation in the size and shape of the intake as speed increases to maintain optimum airflow into the engine.

Chapter 4 is about the compressor, including the fan stage of high bypass-ratio turbofan engines. Lots of diagrams illustrate the complexity of design required and there is an interesting level of detail about the manufacture of components and construction of the engine sections to withstand the huge forces experienced during operation.

The fifth chapter discusses the heart of the engine, the combustion chamber. This is one area where there have been recent developments, so the book does not include for example the TAPS (Twin Annular Pre-mixing Swirler) combustor that has been developed by GE for engines including the GEnx which is to be installed on the new Boeing 787 Dreamliner and Airbus A350 XWB aircraft. However, the basic principle of burning fuel in a controlled manner at the correct fuel:air ratio and the correct temperature applies to all engines, past, present and future.

Chapter 6 is the turbine chapter, or the "compressor in reverse". This section includes a discussion of the heat-resistant materials that are required to withstand the high temperature of the gas that exits the combustion chamber.

Chapter 7 discusses the final stage of the jet engine, the exhaust nozzle. Like the air inlet there is a surprising amount of optimisation required for what is effectively an exhaust pipe.

Having described all stages of the engine, further chapters go on to consider other aspects of jet engine design and performance. Thrust augmentation is discussed in the eighth chapter. This is when thrust is temporarily increased by using afterburners (military aircraft and Concorde) or water injection (civilian aircraft and the Harrier jump jet). Other engine systems essential for operation are described in chapter 9, including the fuel, lubrication, cooling, starting, de-icing and thrust reverser systems.

Chapter 10 briefly discusses environmental considerations including noise reduction and emissions. Again this is an area which has received a lot of attention and advances have been made that are not described in the book. The chapter still provides a useful introduction to the issues and an understanding of the underlying problems.

The final chapter considers engine-airframe integration. The whole aircraft must be designed to ensure optimum performance and best aerodynamic characteristics, resulting in maximum fuel economy.

In summary the book is a really good introduction to the physics behind jet engines. It's not entirely a layman's book, as some of the material is quite technical, but it doesn't require an engineering degree to understand so if you have a real interest in the subject you will be able to appreciate it. Highly recommended.