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Aircraft Propulsion, 2nd Edition by Saeed Farokhi

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CHAPTER 7Combustion Chambers and Afterburners

7.1 Introduction

images

Source: Reproduced with permission from Rolls-Royce plc

To study the mechanism of heat release in an aircraft gas turbine engine combustion chamber, we need to revisit the thermochemistry principles that we learned in our freshman chemistry class. As engineers, we are interested in maximizing the heat release while minimizing the space requirements for the combustion chamber of an aircraft engine. Besides the mechanism of heat release, we are also interested in the rate at which chemical reactions takes place. We may think of it as one characteristic timescale of the problem. The question of rate is governed by the chemical kinetics, which is a subject in thermochemistry. In addition, we hope to understand the characteristic length scales of the problem involved in flame stability and length, which ultimately are tied to the combustion chamber geometry and sizing. In a combustion chamber of an airbreathing engine, we bring a liquid fuel and air together and an ignition source to start off the chemical reaction. We understand that the fuel has to be first vaporized before any reaction can take place between it and the oxygen in the air. We also recognize that a reaction between the oxygen in the air and the fuel must take place upon a collision between the two molecules. Only very energetic collisions result in ...

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