Lefebvre A.H., Ballal D.R. Gas Turbine Combustion: Alternative Fuels and Emissions
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GAS
Turbine
Combustion
THIRD EDITION
Alternative Fuels and Emissions
CRC Press is an imprint of the
Taylor & Francis Group, an informa business
Boca Raton London New York
GAS
Turbine
Combustion
THIRD EDITION
Arthur H. Lefebvre
and
Dilip R. Ballal
Alternative Fuels and Emissions
CRC Press
Taylor & Francis Group
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Boca Raton, FL 33487-2742
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v
Contents
Preface ..................................................................................................................xvii
Authors ................................................................................................................. xix
1. Basic Considerations ......................................................................................1
1.1 Introduction ...........................................................................................1
1.2 Early Combustor Developments .........................................................2
1.2.1 Britain ........................................................................................3
1.2.2 Germany ....................................................................................5
1.2.2.1 Jumo 004 ....................................................................5
1.2.2.2 BMW 003 ...................................................................6
1.2.3 The United States .....................................................................6
1.3 Basic Design Features ...........................................................................8
1.4 Combustor Requirements ....................................................................9
1.5 Combustor Types ................................................................................10
1.5.1 Tubular .................................................................................... 11
1.5.2 Tuboannular ........................................................................... 11
1.5.3 Annular ...................................................................................12
1.6 Diffuser ................................................................................................. 14
1.7 Primary Zone .......................................................................................15
1.8 Intermediate Zone ............................................................................... 16
1.9 Dilution Zone .......................................................................................17
1.10 Fuel Preparation ..................................................................................18
1.10.1 Pressure-Swirl Atomizers ....................................................18
1.10.2 Airblast Atomizer .................................................................19
1.10.3 Gas Injection ..........................................................................20
1.11 Wall Cooling ........................................................................................20
1.11.1 Wall-Cooling Techniques ....................................................22
1.12 Combustors for Low Emissions ........................................................23
1.13 Combustors for Small Engines ..........................................................26
1.14 Industrial Chambers ...........................................................................28
1.14.1 Aeroderivative Engines .......................................................31
References .......................................................................................................33
Bibliography ....................................................................................................33
2. Combustion Fundamentals ........................................................................35
2.1 Introduction .........................................................................................35
2.1.1 Deagration ............................................................................35
2.1.2 Detonation...............................................................................35
2.2 Classication of Flames ......................................................................36
2.3 Physics or Chemistry? ........................................................................37
vi Contents
2.4 Flammability Limits ........................................................................... 37
2.5 Global Reaction-Rate Theory .............................................................38
2.5.1 Weak Mixtures .......................................................................39
2.5.2 Rich Mixtures .........................................................................39
2.6 Laminar Premixed Flames ................................................................41
2.6.1 Factors Inuencing Laminar Flame Speed ........................41
2.6.1.1 Equivalence Ratio ...................................................41
2.6.1.2 Initial Temperature ................................................42
2.6.1.3 Pressure ...................................................................42
2.7 Laminar Diffusion Flames.................................................................42
2.8 Turbulent Premixed Flames ..............................................................43
2.9 Flame Propagation in Heterogeneous Mixtures of Fuel
Drops, Fuel Vapor, and Air ................................................................45
2.10 Droplet and Spray Evaporation .........................................................49
2.10.1 Heat-Up Period ......................................................................50
2.10.2 Evaporation Constant ........................................................... 51
2.10.3 Convective Effects ................................................................52
2.10.4 Effective Evaporation Constant ..........................................52
2.10.5 Spray Evaporation .................................................................54
2.10.6 Some Recent Developments ................................................54
2.11 Ignition Theory ....................................................................................55
2.11.1 Gaseous Mixtures .................................................................55
2.11.2 Heterogeneous Mixtures .....................................................56
2.12 Spontaneous Ignition .........................................................................64
2.13 Flashback ..............................................................................................69
2.14 Stoichiometry .......................................................................................70
2.15 Adiabatic Flame Temperature ...........................................................71
2.15.1 Factors Inuencing the Adiabatic Flame
Temperature .................................................................... 71
2.15.1.1 Fuel/Air Ratio ......................................................71
2.15.1.2 Initial Air Temperature ......................................71
2.15.1.3 Pressure ................................................................72
2.15.1.4 Inlet-Air Vitiation ................................................72
Nomenclature .................................................................................................73
References ....................................................................................................... 74
Bibliography ....................................................................................................77
3. Diffusers .........................................................................................................79
3.1 Introduction .........................................................................................79
3.2 Diffuser Geometry ..............................................................................81
3.3 Flow Regimes ......................................................................................82
3.4 Performance Criteria ..........................................................................83
3.4.1 Pressure-Recovery Coefcient .............................................84
3.4.2 Ideal Pressure-Recovery Coefcient ...................................84
Contents vii
3.4.3 Overall Effectiveness .............................................................85
3.4.4 Loss Coefcient ......................................................................85
3.4.5 Kinetic-Energy Coefcient ...................................................86
3.5 Performance .........................................................................................86
3.5.1 Conical Diffusers ...................................................................87
3.5.2 Two-Dimensional Diffusers .................................................88
3.5.3 Annular Diffusers ..................................................................89
3.6 Effect of Inlet Flow Conditions .........................................................90
3.6.1 Reynolds Number ..................................................................91
3.6.2 Mach Number ........................................................................91
3.6.3 Turbulence ..............................................................................92
3.6.4 Swirl .........................................................................................93
3.7 Design Considerations .......................................................................93
3.7.1 Faired Diffusers .....................................................................93
3.7.2 Dump Diffusers .....................................................................97
3.7.2.1 Inuence of Liner Depth Ratio .............................98
3.7.3 Splitter Vanes ..........................................................................99
3.7.4 Vortex-Controlled Diffuser ................................................100
3.7.5 Hybrid Diffuser .................................................................... 101
3.7.6 Diffusers for Tubular and Tuboannular
Combustors .......................................................................104
3.7.7 Testing of Diffusers ............................................................. 105
3.8 Numerical Simulations..................................................................... 106
Nomenclature ............................................................................................... 108
References .....................................................................................................109
4. Aerodynamics.............................................................................................. 113
4.1 Introduction ....................................................................................... 113
4.2 Reference Quantities ......................................................................... 114
4.3 Pressure-Loss Parameters ................................................................ 114
4.4 Relationship between Size and Pressure Loss .............................. 117
4.5 Flow in the Annulus ......................................................................... 118
4.6 Flow through Liner Holes................................................................ 120
4.6.1 Discharge Coefcient ..........................................................120
4.6.2 Initial Jet Angle ....................................................................123
4.7 Jet Trajectories .................................................................................... 124
4.7.1 Experiments on Single Jets ................................................. 124
4.7.2 Penetration of Multiple Jets ................................................ 126
4.8 Jet Mixing ...........................................................................................129
4.8.1 Cylindrical Ducts .................................................................129
4.8.2 Rectangular Ducts ............................................................... 131
4.8.2.1 Inuence of Density Ratio ................................... 132
4.8.3 Annular Ducts ......................................................................133
viii Contents
4.9 Temperature Traverse Quality ........................................................133
4.10 Dilution Zone Design ....................................................................... 135
4.10.1 Craneld Design Method ..................................................136
4.10.2 NASA Design Method .......................................................137
4.10.3 Comparison of Craneld and NASA
Design Methods ...............................................................137
4.11 Correlation of Pattern Factor Data .................................................. 138
4.12 Rig Testing for Pattern Factor .......................................................... 140
4.13 Swirler Aerodynamics ...................................................................... 140
4.14 Axial Swirlers .................................................................................... 142
4.14.1 Swirl Number ...................................................................... 143
4.14.2 Size of Recirculation Zone ................................................. 144
4.14.3 Flow Reversal ...................................................................... 145
4.14.4 Inuence of Swirler Exit Geometry .................................. 146
4.15 Radial Swirlers................................................................................... 146
4.16 Flat Vanes Versus Curved Vanes .................................................... 147
Nomenclature ............................................................................................... 147
References ..................................................................................................... 149
5. Combustion Performance ......................................................................... 153
5.1 Introduction .......................................................................................153
5.2 Combustion Efciency .....................................................................153
5.2.1 The Combustion Process ....................................................154
5.3 Reaction-Controlled Systems ..........................................................154
5.3.1 Burning Velocity Model ......................................................155
5.3.2 Stirred Reactor Model ......................................................... 159
5.4 Mixing-Controlled Systems ............................................................. 160
5.5 Evaporation-Controlled Systems .................................................... 161
5.6 Reaction- and Evaporation-Controlled Systems ...........................165
5.7 Flame Stabilization ........................................................................... 167
5.7.1 Denition of Stability Performance................................... 167
5.7.2 Measurement of Stability Performance ............................168
5.7.3 Water Injection Technique .................................................. 170
5.8 Bluff-Body Flameholders .................................................................173
5.8.1 Experimental Findings on Bluff-Body Flame
Stabilization ..........................................................................173
5.8.1.1 Homogeneous Mixtures ...................................... 173
5.8.1.2 Heterogeneous Mixtures .....................................177
5.8.2 Summary of Experimental Findings ................................ 179
5.9 Mechanisms of Flame Stabilization ............................................... 179
5.9.1 Homogeneous Mixtures ..................................................... 181
5.9.2 Heterogeneous Mixtures .................................................... 182
5.10 Flame Stabilization in Combustion Chambers ............................. 183
Contents ix
5.10.1 Inuence of Mode of Fuel Injection .................................184
5.10.2 Correlation of Experimental Data .................................... 185
5.11 Ignition ...............................................................................................188
5.12 Assessment of Ignition Performance ............................................. 189
5.13 Spark Ignition .................................................................................... 190
5.13.1 The High-Energy Ignition Unit ........................................190
5.13.2 The Surface Discharge Igniter .......................................... 191
5.13.2.1 Igniter Performance ..........................................192
5.13.2.2 Igniter Design .................................................... 193
5.13.2.3 Igniter Life ..........................................................194
5.14 Other Forms of Ignition ................................................................... 195
5.14.1 Torch Igniter ........................................................................ 195
5.14.2 Glow Plug ............................................................................. 196
5.14.3 Hot-Surface Ignition ...........................................................196
5.14.4 Plasma Jet ............................................................................. 197
5.14.5 Laser Ignition ......................................................................197
5.14.6 Chemical Ignition ...............................................................198
5.14.7 Gas Addition ....................................................................... 199
5.14.8 Oxygen Injection ................................................................. 199
5.15 Factors Inuencing Ignition Performance ..................................... 199
5.15.1 Ignition System ...................................................................200
5.15.1.1 Spark Energy ......................................................200
5.15.1.2 Spark Duration ...................................................200
5.15.1.3 Sparking Rate .....................................................202
5.15.1.4 Igniter Location ..................................................202
5.15.2 Flow Variables .....................................................................203
5.15.2.1 Air Pressure ........................................................203
5.15.2.2 Air Temperature ................................................204
5.15.2.3 Air Velocity .........................................................205
5.15.2.4 Turbulence ..........................................................206
5.15.3 Fuel Parameters ...................................................................207
5.15.3.1 Fuel Type .............................................................207
5.15.3.2 Fuel/Air Ratio ....................................................207
5.15.3.3 Spray Characteristics ........................................208
5.15.3.4 Fuel Temperature ...............................................209
5.16 The Ignition Process .........................................................................209
5.16.1 Factors Inuencing Phase 1 ............................................... 210
5.16.2 Factors Inuencing Phase 2 ............................................... 210
5.16.3 Factors Inuencing Phase 3 ............................................... 211
5.17 Methods of Improving Ignition Performance ............................... 211
5.17.1 Correlation of Experimental Data .................................... 212
Nomenclature ............................................................................................... 214
References ..................................................................................................... 216