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

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3 Experiments on Droplet Array Combustion high flow velocity v (with|v| max = 14.75 m s −1 ). For the round tube of the sample probes used, the hydraulic diameter simplifies as D h = D i [189, 396, 453]: Re= v D h ν , (3.21) D h = 4 A Π . (3.22) The Reynolds number calculates to Re= 67 for the opening and to Re=670 to 830 for the outlet, depending on the varying gas composition and temperature caused by the fresh air entrainment. In either case, it is well below the critical Reynolds number for the respective type of geometry of Re opening,crit = 1100 and Re outlet,crit = 2300, as stated by Sigloch [396]. Consequently, laminar flow can be assumed for the whole combustion chamber, and, in summary, Figures 3.24 and 3.23 reveal that the probe arrangement was specified to allow a spatially and temporally smooth exhaust gas sampling. 116
4 Numerical Modeling and Simulation Numerical simulations of single droplets were conducted in order to complement the experimental findings of this study (cf. Figs. 1.1 and 1.2). Particularly, the physical and chemical mechanisms promoting NO x emissions were systematically investigated including a configuration to elucidate the effect of partial droplet pre-vaporization. Therefore, an approach for modeling and simulation of NO x generation in the gas phase surrounding single burning droplets is presented. Presuming spherical symmetry, with no gravity and no forced convection, the governing equations are derived first. Then, the essentials of forced droplet ignition by an external energy source are introduced. Special attention is given to the modeling of NO x formation, as the numerical work focuses on the adequate combination of detailed chemistry and the pre-vaporization process as well as droplet combustion in hot exhaust gas. Both are technically relevant in liquid fuel combustion. Simplifications are introduced and shown to be appropriate. The model is validated, and finally the portability of the results from the one-dimensional, spherically symmetric model to more complex droplet arrays and cluster regimes is evaluated (Fig. 1.1). 4.1 Description of Involved Processes The main phenomena characterizing droplet combustion are transport of heat and mass as well as chemical reaction [443, 461]. A description of the combustion in flows is, therefore, based upon fluid mechanics coupled with the conservation laws of thermodynamics, including particular transport phenomena of heat and mass transfer. Typical ways to describe droplets in a continuous phase are the Euler-Lagrange and Euler-Euler methods. However, as the droplets given are presumed to be at rest, both approaches are identical, and it is not necessary to differentiate here. Still, the liquid phase of the droplet 117
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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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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 141: 3.3 Numerical Study of the Fluid Dy
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
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
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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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References [1] J.A. Aardenne van, G
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REFERENCES [20] K. Annamalai and W.
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REFERENCES [39] C.H. Beck, R. Koch,
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REFERENCES [462] S.-C. Wong, A.-C.
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