On the Formation of Nitrogen Oxides During the Combustion of ...

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3 Experiments on Droplet Array Combustion W m −1 K −1 . All these property values refer to the gaseous state, as liquid fuel is not part of this CFD simulation. Figure 3.22 illustrates the temporal evolution of the combustion process during the initial second, starting from ignition. Left and right side of the figure depict the vertical middle plane of the combustion chamber with z = 0mm (cf. Fig. 3.7). The left side shows the temperature profile in the gaseous phase with the five fuel sources being the locations of the lowest temperatures, whereas the right side shows the velocity field indicated by the absolute velocity|v|=(vx 2+ v 2 y + v z 2) 2 1 . The velocity vector of the flow is visualized by white streamlines. Being the main subject of this first part of the CFD study, the discharge of hot exhaust gas from the open bottom of the combustion chamber by convection is clearly indicated by the evolution of the temperature and velocity fields. This process is particularly responsible for the temperature field becoming more and more asymmetric along the axis of the droplet array. Here, the initial time (t = 0s) is defined as the time when ignition is enforced by the implemented heat release mechanism. Ignition of the first droplet occurs at t = 29 ms with a local temperature rise to 2118 K. Starting from this local kernel, the flame front propagates along the flammable gas layer, forming a spherical flame around the fuel source. At t = 0.2 s, the flame ball around the first fuel source is fully developed and a temperature of T = T max = 2515 K is indicated. Subsequently, the flame spreads from fuel source to fuel source (Fig. 3.22, from left to right). At t = 0.4s, the fourth droplet is ignited but not yet enclosed by the flame. The ensuing flame propagation and volume expansion due to combustion are clearly observable in combination with the contour plot of absolute velocity |v|. At t = 0.6s, all fuel sources are ignited and the flame stabilizes at a high burning rate k. Still, a small eddy of unburned air prevails in the upper right corner of the droplet array holder before it dissipates around t = 0.8 s. It is a consequence of flame propagation towards the “cold, metallic containment” of the droplet array holder. Finally, the highest velocities within the combustion chamber are observed at the opening in the vicinity of the vertical props with|v| max = 0.595 m s −1 at t = 0.6s. After ignition of the fourth and fifth fuel source, the flow field becomes uniform, as underlined by the white streamlines. The utilized single-step mechanism of Westbrook and Dryer [459] can inherently only be an approximation, as it is trimmed mainly to predict correct flame speeds S L . Thus, it is subject to some restrictions: At flame temperatures 108
3.3 Numerical Study of the Fluid Dynamics Within the Combustion Chamber Temperature T 300 900 1500 2100 K Absolute velocity |v| 0.00 0.04 0.08 0.12 0.16 0.20 m s −1 t = 0.2 s: y z x t = 0.4 s: t = 0.6 s: t = 0.8 s: t = 1.0 s: Figure 3.22: Transient Combustion Process in a Geometric Model of the Combustion Chamber Computed with CFD. The middle plane is shown with z = 0 mm. Time t = 0 s corresponds to the start of heat release (i.e. enforced ignition). Left: temperature distribution (T max = T (t=0.2 s)= 2515K); right: velocity profile of absolute velocity with selected streamlines (|v| max =|v|(t=0.6 s)= 0.595m s −1 ). 109
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TECHNISCHE UNIVERSITÄT MÜNCHEN In
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Vorwort Die vorliegende Arbeit ents
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Kurzfassung Die vorliegende Arbeit
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Contents List of Figures List of Ta
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CONTENTS 5 Results 155 5.1 Droplets
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LIST OF FIGURES xiv 3.3 Droplet Arr
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LIST OF FIGURES 5.19 Progression of
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LIST OF TABLES C.2 Overview of Tele
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NOMENCLATURE g Gravitational force
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NOMENCLATURE σ S Surface tension N
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NOMENCLATURE () T Thermal, temperat
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NOMENCLATURE PAL PAN PDU PFA PFC PH
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1 Introduction In thermal engines t
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1 Introduction 1.3 Oxides of Nitrog
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1 Introduction residence time of th
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1 Introduction Chapter 3 describes
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2 Combustion Theory 2.1.1 Premixed
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2 Combustion Theory molecules by ea
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2 Combustion Theory four types. Out
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2 Combustion Theory ventional combu
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2 Combustion Theory of partial pre-
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2 Combustion Theory Formation of Fu
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2 Combustion Theory Moreover, exper
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2 Combustion Theory For the gas pha
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2 Combustion Theory combustion, ext
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2 Combustion Theory termed “natur
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2 Combustion Theory thin layer of u
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2 Combustion Theory nor generally c
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2 Combustion Theory is assumed to o
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2 Combustion Theory before it follo
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2 Combustion Theory position, which
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2 Combustion Theory 2.3 Kinetic Mod
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2 Combustion Theory 1.2 m s −1 La
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2 Combustion Theory Mole fraction o
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2 Combustion Theory Reburn Miller a
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2 Combustion Theory The results of
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2 Combustion Theory Temperature T 3
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2 Combustion Theory 0.0004 GRI 3.0
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2 Combustion Theory In conclusion,
Page 83 and 84: 3 Experiments on Droplet Array Comb
Page 85 and 86: 3.1 Droplet Combustion Facility and
Page 87 and 88: 3.1 Droplet Combustion Facility C D
Page 89 and 90: 3.1 Droplet Combustion Facility ous
Page 91 and 92: 3.1 Droplet Combustion Facility for
Page 93 and 94: 3.1 Droplet Combustion Facility par
Page 95 and 96: 3.1 Droplet Combustion Facility The
Page 97 and 98: 3.1 Droplet Combustion Facility a c
Page 99 and 100: 3.1 Droplet Combustion Facility •
Page 101 and 102: 3.1 Droplet Combustion Facility Tab
Page 103 and 104: 3.1 Droplet Combustion Facility Fig
Page 105 and 106: 3.2 Measurement Techniques and Data
Page 131 and 132: 3.3 Numerical Study of the Fluid Dy
Page 133: 3.3 Numerical Study of the Fluid Dy
Page 143 and 144: 4 Numerical Modeling and Simulation
Page 145 and 146: 4.2 Basics for Numerical Modeling 4
Page 147 and 148: 4.2 Basics for Numerical Modeling 4
Page 149 and 150: 4.2 Basics for Numerical Modeling n
Page 151 and 152: 4.2 Basics for Numerical Modeling P
Page 153 and 154: 4.2 Basics for Numerical Modeling E
Page 155 and 156: 4.3 Modeling of Ignition In the end
Page 157 and 158: 4.3 Modeling of Ignition 10 W Time
Page 159 and 160: 4.3 Modeling of Ignition Hence, the
Page 161 and 162: 4.4 Modeling of Nitrogen Oxide Form
Page 163 and 164: 4.5 Simulation of Single Droplets t
Page 165 and 166: 4.5 Simulation of Single Droplets e
Page 167 and 168: 4.6 Model Validation with index i
Page 169 and 170: 4.6 Model Validation utilized model
Page 171 and 172: 4.6 Model Validation Figure 4.7 dep
Page 173 and 174: 4.6 Model Validation 340 K Ambient
Page 175 and 176: 4.6 Model Validation Table 4.1: Val
Page 177 and 178: 4.7 Scope and Limitations of Single
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Page 182 and 183: 5 Results In total, it includes 99
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5 Results atmosphere of Figure 5.1
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5 Results 32 g kg −1 2400 K Emiss
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5 Results 4.0 g kg −1 Emission in
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5 Results uses constant spatial pos
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5 Results 16 g kg −1 Emission ind
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5 Results Maximum temperature Tmax
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5 Results Even though the parameter
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5 Results Flame stand-off ratio ζ
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5 Results 5.2.3 Comparison with Mic
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5 Results 0.50 5000 ppm Emission in
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5 Results Ψ = 0.1695 (t Ψ = 5 s):
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5 Results 6.0 g kg −1 Emission in
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5 Results combustion in exhaust gas
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5 Results Flame stand-off ratio ζ
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5 Results D 0 being varied between
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5 Results 0.40 g kg −1 Initial dr
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5 Results A twofold trend was obser
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5 Results 5.6 Recommendations and F
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6 Summary and Conclusions In times
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APPENDIX
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A Chemical Mechanisms The earliest
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A Chemical Mechanisms only deduced
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A Chemical Mechanisms Another, very
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A Chemical Mechanisms the reactions
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B Investigated Conditions There are
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B Investigated Conditions Table B.1
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B Investigated Conditions high mech
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C Design Details of Experiment Equi
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D Raw Data of Microgravity Experime
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SUPERVISED THESES Student Sebastian
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On the Formation of Nitrogen Oxides During the Combustion of ...

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