Appendix A3 Buoyant effects as a function of fuel 's physical properties.

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Citation: Makri, K. (2018). The characterisation of the internal diesel flow and the external
spray structure using laser diagnostics. (Unpublished Doctoral thesis, City, Universtiy of
London)
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THE CHARACTERISATION OF THE INTERNAL
DIESEL FLOW AND THE EXTERNAL SPRAY
STRUCTURE USING LASER DIAGNOSTICS

Kassandra Makri
This thesis is submitted in fulfilment of the requirements for the degree of
Doctor of Philosophy

City, University of London, School of Mathematics, Computer Science and
Engineering, Department of Mechanical Engineering

May 2018
Table of Contents
Chapter 1 Introduction ....................................................................................................................... 24
Chapter 2 Literature review .............................................................................................................. 29
2.1 Diesel fuel background ........................................................................................................ 29
2.1.1 Fundamentals of fuel injection systems .......................................................................... 36
2.1.2 Alternative fuels .............................................................................................................. 38
2.2 Cavitation- Bubble nucleation, growth and collapse dynamics ........................................... 42
2.2.1 Cavitation phenomenon................................................................................................... 42
2.2.2 Cavitation bubble dynamics- Nucleation, Growth, Collapse .......................................... 45
2.2.3 Internal cavitation flow inside diesel injectors ................................................................ 49
2.2.4 Cavitation patterns .......................................................................................................... 51
2.2.5 Internal flow phenomena inside enlarged and real-sized diesel injector nozzles. ........... 58
2.3 Diesel injector deposits ........................................................................................................ 63
2.3.1 Types of deposits in diesel fuel injection systems .......................................................... 64
2.3.2 Deposit formation mechanisms ....................................................................................... 72
2.4 Spray break-up mechanisms ................................................................................................ 75
2.4.1 Sprays emerging from diesel injector nozzles ................................................................. 82
2.5 Optical diagnostics for spray chareacterisation ................................................................... 85
2.5.1 Point Interferometry techniques ...................................................................................... 86
2.5.2 Shadowgraphy - Ballistic imaging technique .................................................................. 90
2.5.3 X-ray absorption technique ............................................................................................. 94
2.5.4 Planar Laser Imaging techniques .................................................................................... 97
Planar Mie imaging technique ................................................................................ 97
Planar Laser Induced Fluorescence (LIF)............................................................. 104
Structured Laser Illumination Planar Imaging (SLIPI) ........................................ 110
Laser Sheet Drop-sizing method (LSD) ............................................................... 114

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Chapter 3 Experimental arrangements and methods.................................................................... 120
3.1 Experimental apparatus ..................................................................................................... 120
3.1.1 Diesel fuel injection system .......................................................................................... 120
3.1.2 Injection control unit ..................................................................................................... 123
3.1.3 Optically accessible diesel injector nozzle .................................................................... 124
3.1.4 Injector holder mount and spray extraction assembly ................................................... 130
3.1.4.1 Assembly of fuel injection components ............................................................... 130
3.1.4.2 Spray extraction assembly .................................................................................... 132
3.2 Optical arrangements ......................................................................................................... 134
3.2.1 Laser optics ................................................................................................................... 134
3.2.2 Internal flow imaging using white light scattering and Laser Induced Fluorescence (LIF)
136
3.2.3 External spray image acquisition using Laser Sheet Drop-sizing (LSD) ...................... 138
3.3 Control setup for high-speed data acquisition ................................................................... 140
3.4 Experimental methodology................................................................................................ 143
3.4.1 Diesel fuels and fuel seeding with fluorescent dye ....................................................... 144
3.4.2 Experimental procedure ................................................................................................ 148
3.4.2.1 Laser imaging experimental procedure ................................................................ 148
3.5 Calibration procedures ....................................................................................................... 152
3.5.1 Gaussian laser profile measurements ............................................................................ 153
3.5.2 Injected fuel mass .......................................................................................................... 154
Chapter 4 Internal flow characterisation using optical diagnostics ............................................. 158
4.1 In-nozzle and sac flow data analysis ................................................................................. 160
4.1.1 Sac bubble formation .................................................................................................... 160
4.1.2 Vorticity in the sac ........................................................................................................ 162
4.1.3 Sac vorticity induced nozzle flow ................................................................................. 165
4.1.4 Analysis on the buoyant effect on the in-nozzle flow ................................................... 167

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4.2 Discussion on the in-nozzle and sac results ....................................................................... 168
4.2.1 Mini-sac diesel vorticity ................................................................................................ 169
4.2.2 Bubble and fluid motion inside the nozzle passages ..................................................... 175
4.2.3 In-nozzle bubble size as a function of time and fuel properties .................................... 193
4.2.4 Bubble formation in the sac – Bubble size and pressure difference analysis ................ 201
4.2.5 Implications of the internal flow on the deposit formation inside the diesel injectors .. 211
4.3 Scattered Fluorescence data analysis ................................................................................. 212
4.4 Discussion on the SFLVF results ...................................................................................... 215
4.4.1 Dependence of Scattered Fluorescence Liquid Volume Fraction (SFLVF) on rail
pressure and needle lift ............................................................................................................... 216
4.4.2 Dependence of Scattered Fluorescence Liquid Volume Fraction (SFLVF) on the
physical properties of the fuels and needle lift ........................................................................... 220
4.5 Summary ............................................................................................................................ 222
Chapter 5 External spray drop-sizing analysis using Laser Sheet Drop-sizing technique ........ 224
5.1 Image processing methodology ......................................................................................... 224
5.1.1 External spray drop-sizing distribution ......................................................................... 224
5.1.2 Diesel spray asymmetry ................................................................................................ 232
5.2 Results and discussion ....................................................................................................... 232
5.2.1 Spray drop-sizing distribution as a function of rail pressure and needle lift ................. 232
5.2.1.1 Diesel spray asymmetry ....................................................................................... 247
5.2.2 Spray drop-sizing distributions as a function of fuel physical properties ..................... 260
5.2.3 Diesel spray asymmetry as a function of fuels’ physical properties ............................. 273
5.3 Flapping spray angles ........................................................................................................ 282
Chapter 6 Investigation of diesel jet structure using Laser Induced Fluorescence (LIF)
technique ............................................................................................................................................ 291
6.1 Image processing methodology for the phenomenological analysis of the sprays ............ 291
6.1.1 Phenomenological analysis of the external diesel sprays .............................................. 291

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6.1.2 Spray structure phenomenology .................................................................................... 292
6.1.3 Liquid Volume Fraction (LVF) distribution along the spray axis ................................. 294
6.1.4 Asymmetry of the diesel sprays .................................................................................... 294
6.2 Results and Discussion ...................................................................................................... 295
6.2.1 Phenomenological analysis of fully developed diesel sprays........................................ 295
6.2.2 Liquid Volume Fraction (LVF) distribution along the central axis of diesel sprays ..... 298
LVF distribution along the spray axis as a function of rail pressure and needle lift
298
5.2.1.2 LVF distributions along the spray axis as a function of fuel’s physical properties
303
6.2.3 LVF distribution across diesel sprays as a function of rail pressure and needle lift ..... 308
6.2.4 Spray LVF distributions as a function of the physical properties of the fuels .............. 320
Chapter 7 Summary and Conclusions ............................................................................................ 331
Appendix A ........................................................................................................................................ 335
Appendix A1 Sac Vorticity Effects on Nozzle flow – Complementary data and results ....... 335
Appendix A2 Correlation between mean in-hole speed and mean in-sac radial flow ............ 351
Appendix A3 Buoyant effects as a function of fuel ‘s physical properties. ............................ 367
Appendix A4 Correlation between in-hole bubble displacement and radial-in sac flow ....... 369
Appendix B ........................................................................................................................................ 373
Appendix B1 Filling, emptying, flushing procedures of the fuel injection system ................ 373
Appendix B2 Injected mass experimental procedure ............................................................. 375
Appendix C ........................................................................................................................................ 376
Publications .................................................................................................................................... 376

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Table of figures
Figure 2.1:Basic schematic of a crude oil refinery system18. ................................................................ 30
Figure 2.2:Typical distillation curve of diesel sample .......................................................................... 32
Figure2.3: Diesel engine characteristics ............................................................................................... 37
Figure 2.4: Schematic diagram of CR injection showing no injection, start of injection and end of
injection stages30. .................................................................................................................................. 38
Figure 2.5: Schematic of the four stages of the cavitation evolution.44 ................................................ 44
Figure 2.6: Caption of the incipient cavitation flow regime53. .............................................................. 52
Figure 2.7: Example of pre-film cavitation flow regime53. ................................................................... 52
Figure 2.8: Example of film cavitation regime53................................................................................... 53
Figure 2.9: Example of string cavitation inside an enlarged diesel injector nozzle62. .......................... 55
Figure 2.10: String cavitation structures linking two neighbouring holes and entering nozzle passages53.
.............................................................................................................................................................. 56
Figure 2.11: Example of needle string cavitation entering the nozzle passage and extending over the
whole length of the nozzle passage56. ................................................................................................... 56
Figure 2.12: Effect of needle lift on spatial and temporal evolution of string cavitation. (a) low needle
lift and (b) higher needle lift 68. ............................................................................................................. 57
Figure 2.13: Possible causes of FIE deposits79. .................................................................................... 64
Figure 2.14: Nozzle coking. a) optical observation, b) Microscopic observation81. ............................. 65
Figure 2.15: Appearance of a typical carboxylate salt85. ...................................................................... 67
Figure 2.16: Comparison of elements found in IIDs and nozzle-hole deposits83. ................................. 67
Figure 2.17: Potential formation mechanism of carboxylate salts80. .................................................... 68
Figure 2.18: Typical appearance of organic amide lacquer deposits85.................................................. 69
Figure 2.19: TEM images (a and b) of carbonaceous particles90. ......................................................... 71
Figure 2.20: Potential deposit formation mechanism8. ......................................................................... 72
Figure 2.21: Images taken 1ms after the needle sealing. Vapour structures are moving towards the sac
inside the lower passage with 1ms time steps16. ................................................................................... 74

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Figure 2.22: Illustration of the near injector region of an atomising spray98. ....................................... 78
Figure 2.23: Basic experimental setup for PDA measurements121. ....................................................... 86
Figure 2.24: Optical configurations of Phase Doppler Anemometry. a) annotation of characteristic
angles, b) Standard optical configuration124. ......................................................................................... 88
Figure 2.25: Schematic representation of shadowgraphy principles..................................................... 90
Figure 2.26: Typical shadowgraph optical arrangement135. .................................................................. 91
Figure 2.27: Representation of ballistic, snake and diffuse photos with a) geometric dependence and b)
time dependence138. ............................................................................................................................... 92
Figure 2.28: Shadowgraph images in a dense spray a) with no time gating, b) time gating to supress
diffuse light. .......................................................................................................................................... 93
Figure 2.29: Schematic of X-ray absorption experimental setup142. ..................................................... 95
Figure 2.30: X-ray images from two different nozzles showing the mass distribution along the
spray142,143. ............................................................................................................................................. 96
Figure 2.31: 3-D volume fraction distributions along both radial and axial direction of the spray144. . 96
Figure 2.32: Light scattering by an induced dipole moment due to incident EM wave145 .................... 98
Figure 2.33: Diagram showing the intensity of scattered light from different scattering modes152. ... 102
Figure 2.34 : Electronic state diagram illustrating the excitation of an atom to a higher energy level by
photon absorption, followed by the emission of fluorescence. ........................................................... 104
Figure 2.35: Possible de-excitation pathways of excited molecules158. ............................................. 105
Figure 2.36: Example of singlet and triplet vibrational states158. ........................................................ 106
Figure 2.37: Representation of a spatially modulated light traversing a scattering medium172. ......... 111
Figure 2.38: An example of 3P-SLIPI application on a cone spray172. ............................................... 112
Figure 2.39: An example of 2P-SLIPI measurement of a premixed Bunsen Flame. a) raw image prior
to any correction methods applied, b) processed 2P-SLIPI image174. ................................................. 113
Figure 2.40: Example of averaged 1P-SLIPI technique172. ................................................................. 114
Figure 2.41: Index of dependence relation on dye concentration159,148. .............................................. 116
Figure 2.42: Comparison between LSD and PDA measurements148. ................................................. 117
Figure 2.43: Comparison of SMD measurements from PDA and LSD methods149. .......................... 118

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Figure 3.1: Schematic of the custom manufactured fuel injection system16. ...................................... 121
Figure 3.2: Needle lift profiles for a modified Denso injector, Jeshani’s mini-sac nozzle and Makri’s
mini-sac nozzle. .................................................................................................................................. 123
Figure 3.3: Simple designs of: (a) a conventional diesel injector nozzle, (b) modified nozzle with acrylic
tip. ....................................................................................................................................................... 125
Figure 3.4: Acrylic nozzle cross sections showing the internal dimensions16. ................................... 125
Figure 3.5: Modified diesel injector nozzle tip showing the view of the holes of interest16. .............. 126
Figure 3.6: Injector tip projective transparent view. ........................................................................... 126
Figure 3.7: Limited optical access through an unpolished surface of the acrylic nozzle. ................... 127
Figure 3.8: Polished nozzle surface, providing good optical access to the nozzle passages. The sac is
located at the centre of the geometry and the passages entering in the sac are at the same height. .... 128
Figure 3.9: Double acting hydraulic ram16. ......................................................................................... 129
Figure 3.10: Operating principle behind a double acting hydraulic cylinder16. .................................. 129
Figure 3.11: Injector holder angled at 60 degrees to prevent any interference with the emerging spray16.
............................................................................................................................................................ 131
Figure 3.12: Assembly of fuel injection components16. ...................................................................... 131
Figure 3.13: Image showing the emerging fuel sprays without interfering with the fuel injection
assembly16. .......................................................................................................................................... 132
Figure 3.14: Spray extraction design16. ............................................................................................... 133
Figure 3.15: Complete assembly of fuel injection components and fuel exhaust extract16. ............... 133
Figure 3.16: Picture showing the cylindrical telescope arrangement and the  50mm mirror. ......... 135
Figure 3.17: Picture showing the mirror and lens assembly above the acrylic nozzle tip. The green line
shows the laser path. ........................................................................................................................... 136
Figure 3.18: Schematic of the optical configuration. .......................................................................... 137
Figure 3.19: Schematic of the internal flow imaging configuration. .................................................. 137
Figure 3.20: Schematic of the LIF/Mie two-channel imaging setup14. ............................................... 139
Figure 3.21: LSD optical arrangement. ............................................................................................... 140

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Figure 3.22: Schematic of synchronisation setup. .............................................................................. 142
Figure 3.23: Schematic of data acquisition setup................................................................................ 143
Figure 3.24: Distillation profiles of the fuels under investigation. ..................................................... 145
Figure 3.25: Molecular structure of Rhodamine B16 ........................................................................... 146
Figure 3.26: An example of a laser sheet intensity profile produced by fuel 1 diesel sample. ........... 153
Figure 4.1: Frame obtained at 6.0ms after SoI (fuel D) showing the in-sac structures represented by the
bright white regions due to white light elastic scattering from the structure interface. (green line: sac
volume, red dotted dash profile needle tip, the yellow dashed line: nozzle holes). ............................ 160
Figure 4.2: (a) Representation of tracking process of an individual structure. y to y are the y-co-
1 3
ordinates in three successive frames (nozzle view from the bottom), (b) an example of bubble tracking
in a series of raw images (the red circles indicate the bubbles of interest). ........................................ 164
Figure 4.3: Picture of the imaging nozzle side. The yellow dashed lines define the boundaries of the
nozzle passages under investigation16. ................................................................................................ 166
Figure 4.4: Images captured between 5.7ms and 6.0ms after the SoI showing the bubble formation in
the sac due to needle sheet cavitation (fuel A, 350bar)16. ................................................................... 169
Figure 4.5: Vorticity decay rates as a function of fuel physical properties at 250bar over a set of 20
injections. ............................................................................................................................................ 170
Figure 4.6: Vorticity decay rates as a function of fuel physical properties at 350bar over a set of 20
injections. ............................................................................................................................................ 172
Figure 4.7: Examples of a. anti-clockwise and b. clockwise flow direction inside the sac volume16. 173
Figure 4.8: Description of flow direction inside the nozzle passages. ................................................ 176
Figure 4.9: Displacement vs time graph, fuel A at 350bar, lower hole, inj.1-5. ................................. 178
Figure 4.10: Displacement vs time graph, fuel A at 350bar, lower hole, inj.6-10. ............................. 179
Figure 4.11: Displacement vs time graph, fuel A at 350bar, lower hole, inj.11-15. ........................... 179
Figure 4.12: Displacement vs time graph, fuel A at 350bar, lower hole, inj.16-20. ........................... 180
Figure 4.13: Displacement vs time graph, fuel A at 350bar, upper hole, inj.1-5. ............................... 180
Figure 4.14: Displacement vs time graph, fuel A at 350bar, upper hole, inj.6-10. ............................. 181
Figure 4.15: Displacement vs time graph, fuel A at 350bar, upper hole, inj.11-15. ........................... 181

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