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

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2 Combustion Theory position, which shifted towards the nozzle. This coincides with larger flow velocities, lower local residence times, and a smaller reaction zone volume. Utilizing a similar configuration, Lyle et al. [260] investigated the NO x formation characteristics of partially premixed turbulent jet flames. They found that the global volumetric NO x production rate cannot be explained by the Zeldovich mechanism alone and different regimes of partial premixing have a significant impact on the absolute NO x values. Employing spatially resolved, linear laser-induced fluorescence (LIF) measurements, Cooper and Laurendeau [84, 85] quantitatively evaluated NO production in preheated lean direct injection (LDI) spray flames at elevated pressures. A pressure scaling of NO is derived from these profiles, which is in line with the results of NO x formation previously obtained by Aigner et al. for a partially premixed injector [13, 88]. Most of these research groups specify the NO x emissions obtained by the emission index EI NOx , as is done in the study at hand. In conclusion, NO x formation is a function of temperature, residence time, excess air, oxygen concentration (N 2 /O 2 ratio), and extent of mixing. To achieve the NO x levels currently set by regulatory agencies, a combination of the following combustion techniques is necessary. Individual solutions may differ significantly for different applications, as for instance in stationary gas turbines or boilers [50, 51, 136, 149, 241, 242, 443]: • Lean (premixed) operated primary zone – resulting in lower local flame temperatures • Reduced combustion zone volume – minimizing residence time • Increased liner pressure drops – increasing turbulence and mixing • Water or steam injection – lowering flame temperatures • Combustion zone cooling by flue gas recirculation – lowering local flame temperatures and depleting the available oxygen • Staged combustion – reducing temperatures and available oxygen After all, most of these approaches involve a direct or indirect deficit of efficiency of the thermal engine. On the downside of such a reduction of efficiency, the NO 2 component typically increases. Moreover, the NO 2 /NO x ratio is very likely to increase with a decrease in the total NO x level [68, 69, 149, 241]. 38
2.2 Theory of Exhaust Gas Formation 2.2.4 Particulate Matter The term “particulate matter” (PM) refers to any substance, except pure water, that exists as a liquid or solid in the atmosphere and is of microscopic or submicroscopic size but has larger dimensions than molecules. Particulate matter may not only result from the direct emission of particles but also from condensation processes or chemical transformation. In order to provide a full description of PM, it is essential to specify the particle concentration, size, chemical composition, state of phase, and morphology [391]. Combustion-generated particulates mainly consist of carbon and have an empirical formula of approximately C 8 H [19]. These carbonaceous particulates are generally formed in gas-phase processes and referred to as soot. Those that are a product of the pyrolysis of liquid hydrocarbon fuels are commonly termed coke or cenospheres. The main constituents of soot are carbon and polycyclic aromatic hydrocarbons (PAHs) [148, 149]. In particular, the fractions containing PAHs were demonstrated to be carcinogenic and even mutagenic [96, 257, 391]. In premixed combustion, emissions of particulate matter mainly result from fuel additives or rich operation, with the latter usually stemming from some type of malfunction [443]. In diffusion flames, the flame luminosity gives an approximate impression of soot distribution. The maximum concentration occurs where the rate of particulate formation equals the rate of its oxidation. Since the presence of carbon particulates increases the radiative power of the flame and, thus, the heat transfer rates, it can be beneficial to operate an industrial system in a particular diffusion flame mode with an enhanced formation of carbon particles [62, 174, 455]. Despite the complex chemistry and physics of soot formation in diffusion flames, Turns [443] summarizes the process by a four-step sequence: • Formation of precursor species • Particle inception • Surface growth and particle agglomeration • Particle oxidation 39
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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
Page 14 and 15: LIST OF FIGURES xiv 3.3 Droplet Arr
Page 16 and 17: LIST OF FIGURES 5.19 Progression of
Page 18 and 19: LIST OF TABLES C.2 Overview of Tele
Page 20 and 21: NOMENCLATURE g Gravitational force
Page 22 and 23: NOMENCLATURE σ S Surface tension N
Page 24 and 25: NOMENCLATURE () T Thermal, temperat
Page 26 and 27: NOMENCLATURE PAL PAN PDU PFA PFC PH
Page 28 and 29: 1 Introduction In thermal engines t
Page 30 and 31: 1 Introduction 1.3 Oxides of Nitrog
Page 32 and 33: 1 Introduction residence time of th
Page 34 and 35: 1 Introduction Chapter 3 describes
Page 36 and 37: 2 Combustion Theory 2.1.1 Premixed
Page 38 and 39: 2 Combustion Theory molecules by ea
Page 40 and 41: 2 Combustion Theory four types. Out
Page 42 and 43: 2 Combustion Theory ventional combu
Page 44 and 45: 2 Combustion Theory of partial pre-
Page 46 and 47: 2 Combustion Theory Formation of Fu
Page 48 and 49: 2 Combustion Theory Moreover, exper
Page 50 and 51: 2 Combustion Theory For the gas pha
Page 52 and 53: 2 Combustion Theory combustion, ext
Page 54 and 55: 2 Combustion Theory termed “natur
Page 56 and 57: 2 Combustion Theory thin layer of u
Page 58 and 59: 2 Combustion Theory nor generally c
Page 60 and 61: 2 Combustion Theory is assumed to o
Page 62 and 63: 2 Combustion Theory before it follo
Page 66 and 67: 2 Combustion Theory 2.3 Kinetic Mod
Page 68 and 69: 2 Combustion Theory 1.2 m s −1 La
Page 70 and 71: 2 Combustion Theory Mole fraction o
Page 72 and 73: 2 Combustion Theory Reburn Miller a
Page 74 and 75: 2 Combustion Theory The results of
Page 76 and 77: 2 Combustion Theory Temperature T 3
Page 78 and 79: 2 Combustion Theory 0.0004 GRI 3.0
Page 80 and 81: 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
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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
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4.3 Modeling of Ignition Hence, the
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4.4 Modeling of Nitrogen Oxide Form
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4.5 Simulation of Single Droplets t
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4.5 Simulation of Single Droplets e
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4.6 Model Validation with index i
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4.6 Model Validation utilized model
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4.6 Model Validation Figure 4.7 dep
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4.6 Model Validation 340 K Ambient
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4.6 Model Validation Table 4.1: Val
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4.7 Scope and Limitations of Single
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4.7 Scope and Limitations of Single
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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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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 [60] F. Buda, R. Bounace
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REFERENCES [80] Comsol AB (Stockhol
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REFERENCES [102] D.L. Dietrich, P.M
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REFERENCES [124] R. Ennetta, M. Ham
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REFERENCES [333] PCB Piezotronics,
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