vii
TABLE OF CONTENTS
CHAPTER
1
2
TITLE
PAGE
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
xi
LIST OF FIGURES
xii
LIST OF SYMBOLS
xvi
LIST OF ABBREVIATIONS
xix
LIST OF APPENDICES
xx
INTRODUCTION
1
1.1
Research Background, Motivations and Outlines
1
1.2
Combustion Issues
4
1.3
Problem Statement
4
1.4
Research Objectives
6
1.5
Research Questions
6
1.6
Significance of the Study
7
1.7
Major Contribution
7
1.8
Thesis Outline
8
LITERATURE REVIEW
9
2.1
Introduction
9
2.2
Size-scale Concept
11
2.3
Fluid Issues in Meso-Scale Combustor
13
viii
2.4
Thermal Issues in Meso-Scale Combustor
14
2.5
Flame Classification
16
2.6
Mixing of Fuel-Air in a Meso-Scale Combustor
17
2.7
Flame Stability in Meso-scale Combustor
18
2.8
Combustion of Natural Gas
20
2.9
NOx Production Mechanism
20
2.10 Small Scale Power Generation
21
2.11 Experimental Study on the Small Scale Combustion
22
2.12 Numerical Study on the Small Scale Combustion
24
2.13 Swirling Flames and Swirl Number Definition
27
2.14 Review of Vortex Flame
33
2.15 Conceptual Asymmetric Vortex Combustor: Present Work
38
2.16 Mathematical Modeling
39
2.16.1 Transport Governing Equation
39
2.16.1.1 Continuity Equation
40
2.16.1.2 Momentum Equation
40
2.16.1.3 Energy Equation
41
2.16.1.4 Species Equation
42
2.16.1.5 Turbulence Modeling
42
2.16.2 Modeling Reacting Flow (Eddy Dissipation Model)
3
44
2.17 Summary
45
RESEARCH METHODOLOGY
46
3.1
Introduction
46
3.2
Research Hypothesis
47
3.3
Research Methodology Flowchart
47
3.4
Research Scope and Limitations
50
3.4.1 General Methodological Scope
50
3.4.2 Computational Scope
50
3.5
Design and Fabrication of Meso-scale Combustion
50
3.6
Experimental Setup of Meso-Scale Vortex Flames
52
3.6.1 Experimental Test Procedure
54
3.6.2 Test Preparation
54
3.6.3 Combustion Test Procedure
54
ix
Apparatus
55
3.7.1 Fuel and Air Supply System
55
3.7.2 Fuel (Natural Gas)
56
3.7.3 Product Gas Measurements
57
3.7.4 Temperature Measurements
58
3.7.5 High Speed Camera, Phantom v710
58
3.8
Uncertainty Analysis
58
3.9
Computational Study of Vortex Combustion
59
3.9.1 Grid Independence Test
62
3.7
4
3.10 Combustion Efficiency
64
3.11 Combustible Mixture and Preparation
65
3.12 Pearson Correlation Coefficient (r)
65
3.13 Summary
66
RESULTS AND DISCUSSION
67
4.1
Introduction
67
4.2
Stability of Natural Gas Flame with Air
68
4.3
Quenching Diameter
69
4.4
Mixing Dynamics
70
4.4.1 Mixing in Vortex Combustion Chamber
70
4.4.2 Velocity and Swirl Number
73
Combustion Temperature
78
4.5.1 Temperature Pattern for Natural Gas with Air
78
4.5.2 Exhaust Temperature of Natural Gas Combustion
86
4.5.3 Wall Temperature
88
4.5.4 Heat Loss from the Wall
91
Exhaust Gas Analysis
93
4.6.1 NOx Emission Characteristics
93
4.6.2 Concentration of O2 and CO2
96
4.5
4.6
4.7
Vortex Structure
100
4.8
Effect of Chamber Scale on Flame Stability
101
4.9
The Photograph of Vortex Flame
105
4.10 Meso-scale Vortex Flame Height
107
4.11 Combustion Efficiency
108
x
5
4.12 Statistical Analysis
109
4.13 Summary
110
CONCLUSIONS AND RECOMMENDATIONS
111
5.1
Conclusion
111
5.2
Future Works
113
REFERENCES
APPENDICES A-C
114
129-133
xi
LIST OF TABLES
TABLE NO.
2.1
TITLE
PAGE
Numerical studies on the micro/meso-combustors in the
literatures
25
3.1
Fuel and air supply system
56
3.2
Natural gas combination
57
3.3
Characteristic and accuracy of Gas analyzer
57
3.4
Boundary conditions
61
3.5
Dimensions of the meso-scale vortex combustors (All dimensions
are mm)
4.1
Values of least-square regression constants for different mass
flow rate of air
4.2
62
Correlation of experimental and numerical results
95
109
xii
LIST OF FIGURES
FIGURE NO.
1.1
TITLE
PAGE
Comparison of specific power and energy generated through
different power devices [6]
2
2.1
Essential terminology of the present research topic
10
2.2
Combustion classifications [29]
12
2.3
Classification of flames according to (a) temporal steadiness
(b) a mixing between fuel and oxidizer (c) stability, with
reference to their flow regime [16]
16
2.4
(a) Combustor configuration (b) Wall section of combustor [71]
24
2.5
Schematic of the computational domain of combustor with the
boundary conditions [73]
26
2.6
Schematic of the micro combustor with a bluff body [77]
27
2.7
Visualizations of swirling flames (a) Premixed methane/air
(b) Premixed propane/air [82]
2.8
Visualizations of swirling flames (a) F-TACLES model
(b) Cylindrical quartz with 16 injectors [83,84]
2.9
29
Flow structures induced by a swirling injector (a) Gas turbine
model (b) Temperature isosurface [88,89]
2.11
28
Practical swirling injector arrangements (a) Gas turbine GT26
(b) Two radial swirlers (c) Premixed injector [86,87]
2.10
28
30
Examples of axial and radial swirlers (a) axial swirling vanes
(b) radial swirlers with blades [82]
31
2.12
Examples of mixing axial and radial swirlers [96,97]
32
2.13
PAW combustor depicted by (a) elevation view and (b) cross
section at the inlet plane [21]
33
xiii
2.14
Direct photographs of (a) symmetrically-fueled flames in PAW
(b) Asymmetrically-fueled flames in PAW [21]
35
2.15
Conventional vortex combustor [25]
36
2.16
(a) The size of the meso-scale vortex combustor compared to a
small coin (b) A schematic of the oxidizer and fuel admission
configuration [109]
2.17
36
Schematic of (a) vortex chamber for studying the non-reactive
vortex flow (b) the meso-scale vortex combustor showing the
tangential inlet and outlet of air and exhaust respectively and
the radial inlet of the fuel [110]
2.18
37
The design of meso-scale burner zone (a) isometric view (b) top
view
39
3.1
Flowchart of the research methodology
49
3.2
Meso scale vortex chamber
51
3.3
Two vortex chambers fabricated by steel
52
3.4
Schematic of the experimental platform of the vortex combustor
53
3.5
The design of the vortex combustor
60
3.6
Grid independence test
63
3.7
Computational domain of vortex combustor
64
4.1
The stability region of vortex flames in meso-scale combustor
69
4.2
Temperature contour for different scales of vortex combustor
70
4.3
The combined velocity vector plot with natural gas mole fraction
plot at fuel flow rate = 40mg/s and stoichiometric condition
4.4
Pathlines of fuel inlet at different fuel flow rate at stoichiometric
condition
4.5
71
72
Pathlines of air inlet at different mass flow rate at stoichiometric
condition
72
4.6
Stream line lengths of various mass flow rates
73
4.7
Predicted tangential velocity profiles at different axial distances
with mass flow rate of inlet air a = 40 mg/s, b = 80 mg/s, c = 120
mg/s and d = 170 mg/s respectively
4.8
75
The contours of velocity on cross sections z = 1.5, 5, 10, 15, 20
and 25 in the chamber with different mass flow rate at φ = 1
76
xiv
4.9
Relation inlet air velocity in the pipe with air velocity in the
combustor entrance in different mass flow rate at φ = 1
4.10
Axial evolution of swirl number in the chamber at ambient
pressure
4.11
77
78
Temperature contours of the reacting flow inside the vortex
combustor for different mass flow rate. The first category is
at plane (A) and the second category is at plane (B)
4.12
80
Temperature distributions along the central axis of vortex
combustion for different mass flow rate of air
82
4.13
Temperature distributions along the combustor height
84
4.14
Temperature of inlet air supply to combustor at different mass
flow rate
4.15
Temperature of inlet air supply to combustor at different
equivalence ratio
4.16
85
85
Exhaust temperature of natural-gas combustion at varying mass
flow rate a = 40 mg/s, b = 80 mg/s, c = 120 mg/s and d = 170 mg/s 88
4.17
Schematic of meso-scale vortex combustion, red line is length of
inside chamber wall and outside chamber wall
4.18
89
Wall temperature of meso vortex combustion at varying mass
flow rate of inlet air (40, 80, 120 and 170 mg/s)
91
4.19
Heat loss of meso-scale chamber at different mass flow rates
92
4.20
Variation of NOx concentration respect to mass flow rate of inlet
air (40, 80, 120 and 170 mg/s)
4.21
Mole fraction of O2 in the exhaust gas for different mass flow
rate of inlet air (40, 80, 120 and 170 mg/s)
4.22
97
Mole fraction of CO2 in the exhaust gas for different mass flow
rate of inlet air (40, 80, 120 and 170 mg/s)
4.23
95
99
Isocontours of the statistical average of (a) pressure and
(b) azimuthal velocity
100
4.24
Isocontours of the swirling strength in different Reynolds number 101
4.25
Flame stability in two different combustor scales
102
4.26
Dimensionless axial evolution of swirl number
103
4.27
Variation of NOx concentrations in two different combustor
scales
104
xv
4.28
Heat losses from the wall for two different meso-scale
combustors
4.29
105
Digital photos with daylight settings of (a) two stoichiometric
fuel jets without the air vortex and (b) stoichiometric vortex
flame
4.30
Direct photographs of the vortex flame at different values of
equivalence ratio (φ)
4.31
106
107
Predicted flame height and maximum flame temperature as
functions of equivalence ratio at Reynolds number equal to 308
108
xvi
LIST OF SYMBOLS
S
-
Area (m2)
L
-
Linear system characteristic
V
-
Volume (m3)
m
-
Mass (kg)
Fg
-
Gravitational force (N)
Pg
-
Pressure force due to gravitational (Pa)
μ
-
Viscosity (N.s/m2)
P
-
Pressure (Pa)
Da
-
Damkohler Number
Sn
-
Swirl number
τr
-
Residence time (s)
τc
-
Time scale of chemical kinetic (s)
Pr
-
Prandtl number
Sc
-
Schmidt number
Le
-
Lewis number
ρ
-
Density (kg/m3)
k
-
Thermal conductivity (W/m.K)
CP
-
Specific heat at the constant pressure (J/K)
D
-
Diameter (m)
α
-
Thermal expansion rate (1/K)
V
-
Velocity (m/s)
xvii
ui
-
Velocity components (m/s)
Re
-
Reynolds number
Pe
-
Peclet number
Pr
-
Prandtl number
Ea
-
Activation energy (kJ/mol)
R
-
Gas constant (J/mol.K)
Nu
-
Nusselt number
Γ
-
Diffusion coefficient (m2/s)
keff
-
Effective conductivity (W/mK)
Sh
-
Heat source term (J)
E
-
Energy related to static enthalpy (J)
Jj,I
-
Diffusion flux
h
-
Enthalpy (J)
h
-
Heat transfer coefficient (W/m2K)
Ri
-
Reaction rate (m3/s)
mi
-
Mass fraction
ppm
-
Part per million
μt
-
Kinematic viscosity (m2/s)
Ri
-
Production of net rate
Si
-
Rate of formation by dispersed phase
φ
-
Equivalence ratio
T
-
Temperature (K)
mf
-
Mass flowrate of fuel (kg/s)
ma
-
Mass flow rate of air (kg/s)
ηt
-
Thermal efficiency
xviii
Hc
-
High heating value (MJ/kg)
δ
-
Flame thickness (m)
λ
-
Mean free path (m)
δij
-
Kronecker delta
k
-
Turbulence kinematic energy (J/kg)
ε
-
Dissipation rate (J/kg.s)
Yf
-
Mass fraction of fuel
Yo
-
Mass fraction of oxidizer
Yp
-
Mass fraction of products
υ
-
Stoichiometric oxidizer to fuel mass ratio
xix
LIST OF ABBREVIATIONS
CFD
-
Computational Fluid Dynamic
CRZ
-
Central Recirculation Zone
EGR
-
Exhaust Gas Recirculation
EDM
-
Eddy Dissipation Model
FOV
-
Field of View
LHV
-
Lower Heating Value
MEM’s
-
Micro Electrical Mechanical System
NOx
-
Nitrogen Oxide
PWC
-
Princeton University Whirl Combustor
PIV
-
Particle Image Velocimetry
PLIF
-
Planar Laser-Induced Fluorescence
RANS
-
Reynolds-Averaged Navier Stokes Equations
RNG
-
Re-Normalization Group
SRZ
-
Secondary Recirculation Zone
TKE
-
Turbulent Kinetic Energy
xx
LIST OF APPENDICES
APPENDIX
TITLE
PAGE
A
List of publications
126
B
Calibration sheet of apparatus
127
C
The details of calculations
130