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

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5 Results Flame stand-off ratio ζ 8 6 4 Exhaust atmosphere: φ = 0.600 (T g,0 = 1781.4 K) Exhaust atmosphere: φ = 0.850 (T g,0 = 2148.2 K) Exhaust atmosphere: φ = 0.925 (T g,0 = 2228.0 K) 2 Hot air atmosphere: T g,0 = 1781.4 K Hot air atmosphere: T g,0 = 2148.2 K Hot air atmosphere: T g,0 = 2228.0 K 0 0.0 0.2 0.4 0.6 0.8 1.0 Dimensionless time t/∆t sim Figure 5.19: Progression of Flame Stand-off for Droplets Burning in Atmospheres of Air and Exhaust. The initial gas phase temperatures are chosen to be identical for the two depicted cases, and they correspond to the exhaust atmosphere of a premixed flame of the equivalence ratio φ= 0.600, 0.850, and 0.925. oxygen atmosphere. As illustrated in Figure 5.20, a decrease of its oxygen concentration causes an increase in the time-averaged flame stand-off ratio ζ. On the other hand, an increase of T g ,0 only leads to a slight decrease of ζ for air atmospheres with a constant concentration of oxygen. Thus, the decrease in oxygen dominates the parameter ζ over the increase in temperature. Since the flame in this case is shifted away from the droplet surface, the droplet’s influence on NO x formation declines and the gas atmosphere gains predominance (cf. Fig. 5.18). Generally, the flame stand-off ratios of the present study are altogether consistent with literature. Similar results on the impact of atmosphere dilution are reported by Bae and Avedisian [30], Dietrich et al. [102], and Jin and Shaw [198]. For the influence of the initial temperature T g ,0 , similar effects can be observed in the studies of Jackson and Avedisian [192], Xu et al. [465, 467], and Cuoci et al. [92], despite major variations of the initial droplet diameter. 184
5.4 Influence of Droplet Size Mole fraction of O2 XO2 0.2 0.1 0.0 Time-averaged flame stand-off ratio ζ 4 2 Hot air atmosphere Exhaust atmosphere 0 1600 1800 2000 2200 K Initial temperature T g,0 Figure 5.20: Dependence of Flame Stand-off on Temperature and Initial Oxygen Concentration. The time-averaged flame stand-off ratio ζ indicates the flame position, and the initial mole fraction of oxygen X O2 stands for the ratio of oxidant and inert gas. 5.4 Influence of Droplet Size Generally, a practical spray can be regarded as a spectrum of droplets of different sizes. For technical atomizers, this spectrum typically ranges from a few micrometers up to around 500µm [244]. Since the combustion characteristics of such a spray vary considerably with the prevailing mean droplet size and droplet size distribution, this section rounds off the parameters considered here and relevant to NO x formation, that can be influenced by technical means. The results were obtained from numerical as well as experimental studies, and single droplets as well as droplet arrays were investigated. Chapter 5.1 describes droplets burning in the atmosphere of hot exhaust gas of different equivalence ratios φ. The same numerical configuration is used to study the impact of the initial droplet diameter D 0 on NO x formation, with 185
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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,
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3 Experiments on Droplet Array Comb
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3.1 Droplet Combustion Facility and
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3.1 Droplet Combustion Facility C D
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3.1 Droplet Combustion Facility ous
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3.1 Droplet Combustion Facility for
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3.1 Droplet Combustion Facility par
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3.1 Droplet Combustion Facility The
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3.1 Droplet Combustion Facility a c
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3.1 Droplet Combustion Facility •
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3.1 Droplet Combustion Facility Tab
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3.1 Droplet Combustion Facility Fig
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3.2 Measurement Techniques and Data
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3.3 Numerical Study of the Fluid Dy
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4 Numerical Modeling and Simulation
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4.2 Basics for Numerical Modeling 4
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4.2 Basics for Numerical Modeling 4
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4.2 Basics for Numerical Modeling n
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4.2 Basics for Numerical Modeling P
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4.2 Basics for Numerical Modeling E
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4.3 Modeling of Ignition In the end
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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
Page 179: 4.7 Scope and Limitations of Single
Page 182 and 183: 5 Results In total, it includes 99
Page 184 and 185: 5 Results atmosphere of Figure 5.1
Page 186 and 187: 5 Results 32 g kg −1 2400 K Emiss
Page 188 and 189: 5 Results 4.0 g kg −1 Emission in
Page 190 and 191: 5 Results uses constant spatial pos
Page 192 and 193: 5 Results 16 g kg −1 Emission ind
Page 194 and 195: 5 Results Maximum temperature Tmax
Page 196 and 197: 5 Results Even though the parameter
Page 198 and 199: 5 Results Flame stand-off ratio ζ
Page 200 and 201: 5 Results 5.2.3 Comparison with Mic
Page 202 and 203: 5 Results 0.50 5000 ppm Emission in
Page 204 and 205: 5 Results Ψ = 0.1695 (t Ψ = 5 s):
Page 206 and 207: 5 Results 6.0 g kg −1 Emission in
Page 208 and 209: 5 Results combustion in exhaust gas
Page 212 and 213: 5 Results D 0 being varied between
Page 214 and 215: 5 Results 0.40 g kg −1 Initial dr
Page 216 and 217: 5 Results A twofold trend was obser
Page 218 and 219: 5 Results 5.6 Recommendations and F
Page 221 and 222: 6 Summary and Conclusions In times
Page 223: APPENDIX
Page 226 and 227: A Chemical Mechanisms The earliest
Page 228 and 229: A Chemical Mechanisms only deduced
Page 230 and 231: A Chemical Mechanisms Another, very
Page 232 and 233: A Chemical Mechanisms the reactions
Page 234 and 235: B Investigated Conditions There are
Page 236 and 237: B Investigated Conditions Table B.1
Page 238 and 239: B Investigated Conditions high mech
Page 240 and 241: C Design Details of Experiment Equi
Page 250 and 251: D Raw Data of Microgravity Experime
Page 256 and 257: SUPERVISED THESES Student Sebastian
Page 259 and 260: References [1] J.A. Aardenne van, G
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On the Formation of Nitrogen Oxides During the Combustion of ...

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