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

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3 Experiments on Droplet Array Combustion ter [129, 222, 280, 317, 376, 429]. These effects become increasingly important at a late stage of droplet burning, when the droplet diameter approaches the diameter of the quartz fiber. A broad discussion on the general use of suspension fibers can be found in the work of Mikami et al. [282], Shih and Megaridis [395], and Farouk and Dryer [130]. These studies include a comparison of the relevant geometric and thermal properties as well as an evaluation of the particular vaporization and burning rates, the flame stand-off ratio, and the effect of thermal radiation. According to the experimental work of Avedisian and Callahan [28], the evolution of the droplet diameter during droplet burning shows an excellent conformity for free and fiber supported droplets. Farouk and Dryer [130], on the other hand, predict a significant influence of the suspension fiber based on their numerical simulations, using a transient onedimensional, spherically symmetric droplet combustion model that implicitly accounts for the effects of a supporting fiber. The main argument in favor of using a droplet suspension technique at all within the present experimental setup is the realization of a well-defined linear droplet array. Multiple droplets can be generated simultaneously, and droplet drift during the burning period can be avoided, including the most critical ignition phase. The X-shaped fiber pairs stabilize the droplets. Droplets up to 1.5 mm can be tethered this way under normal gravity conditions, while much larger droplets are realizable in microgravity. Furthermore, the retraction of the fine glass tubes from the fiber intersections, after completion of the fueling process, generally has no negative effect on the droplet suspension. Recalling the scientific requirements for the present experiment, the droplet array holder has to fulfill the following technical specification: • Equal horizontal distances between the different fiber pairs • Equal vertical level of all fiber intersections • Droplet stabilization at fiber intersections, especially during the critical acceleration phase of the droplet array lifting devices • Support of the droplet ignition system The droplet array holder is a stainless steel frame made of four parts that are bolted together. It is highly important to have accurately manufactured single 66
3.1 Droplet Combustion Facility parts to guarantee that the fiber intersections are located at their exact positions. In each case, two SiC fibers are stretched across the two horizontal beams and glued onto them in a crossing pattern normal to the direction of flame spread and at an angle of about 17° (see Fig. 3.6). An initial load must be similarly applied to all fibers during this process until curing is complete. In previous work, four instead of two beams were used for this setup, allowing a wider opening angle of the fiber pairs, and thus an even better balanced restoring moment [206, 207, 282, 283]. However, the current design was restricted by the combustion chamber design (Chap. 3.1.3) and the investigation of high pre-vaporization rates Ψ, and thus kept as slim as possible. Table 3.1 lists the key data of the utilized droplet array holders. The inter-droplet distance S is chosen as a multiple of 1.5 mm, which was the nominal droplet diameter D 0,nom of the TEXUS-46 sounding rocket campaign (Fig. 3.1). Table 3.1: Geometric Data of Investigated Droplet Arrays. Number of Inter-droplet Total length of droplets N distance S in mm droplet array L in mm 5 18.0 72 9 9.0 72 13 6.0 72 17 4.5 72 Apart from the SiC fibers, a hot-wire igniter made of iron-chrome alloy is integrated on either side of the droplet array holder (Fig. 3.6). However, only one igniter is nominally used for initiating combustion on the closest droplet. The second igniter is for redundancy purposes as well as for varying degrees of droplet vaporization. 3.1.3 Combustion Chamber After the generation of a droplet array at room temperature, it is inserted into the preheated combustion chamber by lifting the droplet array holder (Fig. 3.3). Figure 3.7 provides two views of the thermally insulated combustion chamber. The transparent view shows the vertical middle along the axis 67
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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
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 64 and 65: 2 Combustion Theory position, which
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
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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
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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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