Engineering Combustion Essentials Engineering Combustion Essentials By David S-K. Ting Engineering Combustion Essentials By David S-K. Ting This book first published 2018 Cambridge Scholars Publishing Lady Stephenson Library, Newcastle upon Tyne, NE6 2PA, UK British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Copyright © 2018 by David S-K. Ting All rights for this book reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the copyright owner. ISBN (10): 1-5275-1414-5 ISBN (13): 978-1-5275-1414-0 Combustion is essential to human survival, and so is learning. This book aims at sparking inquisitive minds on fire, setting off a series of positive chain reactions which beautify everyday and future combustion. “At times our own light goes out and is rekindled by a spark from another person. Each of us has cause to think with deep gratitude of those who have lighted the flame within us.” —Albert Schweitzer CONTENTS Preface ....................................................................................................... xii Acknowledgements .................................................................................. xiii Chapter One ................................................................................................. 1 Introduction 1.1 What is Combustion? ....................................................................... 2 1.2 Combustion in Applications ............................................................. 4 1.3 A Highlight of Combustion Science Development .......................... 6 1.3.1 The Phlogiston Theory ............................................................ 7 1.3.2 Antoine Lavoisier .................................................................... 8 1.3.3 Other Combustion Milestones ................................................. 9 1.4 Historical Perspective of Combustion Technology ........................ 10 1.4.1 Lighting ................................................................................. 10 1.4.2 Steam Boilers ........................................................................ 12 1.4.3 Internal Combustion Engines ................................................ 14 1.4.4 Gas Turbines ......................................................................... 16 1.5 Book Layout .................................................................................. 18 Chapter Two .............................................................................................. 21 Thermochemistry 2.1 Introduction .................................................................................... 23 2.2 Fuels ............................................................................................... 27 2.3 Stoichiometry ................................................................................. 27 2.3.1 Air/Fuel Ratios ...................................................................... 28 2.3.2 Equivalence Ratios ................................................................ 30 2.3.3 Reactive Additives ................................................................ 31 2.4 Thermodynamic Property Relations .............................................. 32 2.4.1 Equation of State ................................................................... 32 2.4.2 Calorific Equations of State .................................................. 32 2.4.3 Dalton’s Law of Partial Pressures ......................................... 34 2.4.4 Amagat’s Law of Additive Volumes ..................................... 35 2.4.5 Ideal Gas Mixtures ................................................................ 36 viii Contents 2.5 Thermodynamic Laws and Functions ............................................ 37 2.5.1 The First Law of Thermodynamics for a Fixed Mass (Closed System) ........................................................................ 39 2.5.2 The First Law of Thermodynamics for a Control Volume .... 44 2.6 Enthalpy: Vaporization, Formation, Combustion .......................... 45 2.6.1 Latent Heat of Vaporization .................................................. 45 2.6.2 Heat of Formation ................................................................. 45 2.6.3 Heat of Combustion .............................................................. 46 2.6.4 Heating Value ........................................................................ 48 2.7 Adiabatic Flame Temperature ........................................................ 49 Chapter Three ............................................................................................ 55 Chemical Equilibrium and Dissociation 3.1 Introduction .................................................................................... 56 3.2 The Second Law of Thermodynamics ........................................... 57 3.2.1 Thermodynamic Functions .................................................... 58 3.3 Equilibrium of Thermodynamic Systems ...................................... 59 3.3.1 Constant-Volume Process ..................................................... 61 3.3.2 Constant-Temperature Process .............................................. 63 3.3.3 Constant-Pressure-and-Temperature Process ........................ 64 3.3.4 Chemical Potential Minimization .......................................... 65 3.3.5 Equilibrium Constants ........................................................... 66 3.4 Dissociation ................................................................................... 68 Chapter Four .............................................................................................. 81 Chemical Kinetics 4.1 Introduction .................................................................................... 82 4.2 Global versus Elementary Reactions ............................................. 83 4.2.1 Global Reactions ................................................................... 83 4.2.2 Order of Reaction .................................................................. 86 4.3 Elementary Reactions .................................................................... 86 4.3.1 Molecularity of a Reaction .................................................... 87 4.3.2 The Law of Mass Action ....................................................... 87 4.4 Types of Chemical Reactions ........................................................ 88 4.4.1 First-Order Reactions ............................................................ 90 4.4.2 Second-Order Reactions ........................................................ 91 4.4.3 Consecutive Reactions .......................................................... 94 4.4.4 Opposing or Reversible Reactions ........................................ 95 4.4.5 Chain Reactions ..................................................................... 99 4.5 The Arrhenius Law and the Collision Theory .............................. 102 Engineering Combustion Essentials ix 4.6 Pressure and Temperature Effects on Reaction Rate ................... 108 4.6.1 Pressure Effect ..................................................................... 108 4.6.2 Temperature Effect .............................................................. 109 4.7 Net Production Rates ................................................................... 109 4.8 Chemical Time Scales .................................................................. 110 Chapter Five ............................................................................................ 113 Laminar Premixed Flames 5.1 Introduction .................................................................................. 115 5.2 Laminar Flame Speed, Flame Propagation Speed, and Mass Burning Rate ................................................................................ 116 5.2.1 The Freely Propagating Planar Flame ................................. 119 5.2.2 The Freely Propagating Spherical Flame ............................ 120 5.2.3 The Confined Spherical Flame ............................................ 122 5.3 The Structure of Combustion Wave ............................................. 125 5.4 Laminar Flame Speed Measurements .......................................... 128 5.4.1 The Non-Existing Ideal Planar Combustion Wave ............. 128 5.4.2 A Stationary Spherical Flame .............................................. 129 5.4.3 Common Flame Observation Methods ................................ 131 5.4.4 Bunsen Burner ..................................................................... 133 5.4.5 Soap Bubble ........................................................................ 136 5.4.6 Constant Volume Chamber ................................................. 136 5.4.7 Flat Flame Burner ................................................................ 138 5.4.8 Stagnation and Opposed Flame Burners ............................. 139 5.5 Premixed Laminar Flame Theories .............................................. 139 5.5.1 Thermal Theory ................................................................... 140 5.5.2 Thermal Species - Thermal Theory with Species Diffusion ................................................................................. 141 5.5.3 Modern Comprehensive Theories or Models ...................... 144 Chapter Six .............................................................................................