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

More documents

Recommendations

Info

5 Results 5.6 Recommendations and Future Tasks The study at hand is focused on the combustion of single droplets and droplet arrays under microgravity conditions. While studying these droplet setups under idealized conditions, the understanding of particular physical and chemical processes could be improved. Nevertheless, convective flow around the droplets also has a major influence on heat and mass transfer, and the interaction of droplets is significant in sprays. Both effects could, in part, be accounted for by the experimental part of this study. Besides, an extended, two-dimensional model was developed in cylindrical coordinates to accommodate those aspects. Its implementation into the software package Cosilab ® and the multiphysics and reaction engineering environments of COMSOL ® [80–83] was carried out successfully. However, neither implementation was capable of providing results comparable to those of the one-dimensional model with respect, in particular, to NO x formation. This shortcoming was due to numerical instabilities, on the one hand, and combustion chemistry too complex for the CFD framework, on the other hand. In addition, droplet burnout within a droplet array is achieved at different instants, as the droplets vaporize and burn at different rates depending on their individual state of preheating and combustion. However, a droplet of zero radius cannot be represented by the numerical model, and thus calculations have to be stopped, once the size of a droplet drops below a certain threshold. Then, the interface conditions have to be changed before continuing simulation of the remaining droplets. Nonetheless, such a two-dimensional model is capable of representing interactions in droplet arrays. The additional spatial dimension allows to model forced ignition even more realistically. It is also possible to study the influence of convective flow on single droplets or along a droplet array. Various droplet arrays can be investigated regarding droplet size and inter-droplet distance. Additional findings with regard to flame shape and temperature distribution can provide a deeper insight into the complex processes within spray flames. In general, further work needs to be carried out to develop a comprehensive understanding of NO x formation in partially pre-vaporized droplet and spray flames. It should focus on the ambient setting, including temperature, pressure, and atmospheric composition, as well as secondary effects of vapor- 192
5.6 Recommendations and Future Tasks ization and combustion, including droplet lifetime, ignition delay times, and peak temperature. The impact of the inter-droplet distance on the combustion process is also to be investigated, as it directly affects flame propagation and flame shape. Apart from modeling ignition by a well-defined volumetric heat source, it can also be achieved by convection of hot gas towards the first droplet. Research on reduced chemical kinetics as well as appropriate postprocessing procedures is indispensable, provided that computational power remains moderately constant. This will help to reduce the number of species and elementary reactions represented in the calculations. 193
Page 1:
TECHNISCHE UNIVERSITÄT MÜNCHEN In
Page 5 and 6:
Vorwort Die vorliegende Arbeit ents
Page 7 and 8:
Kurzfassung Die vorliegende Arbeit
Page 9 and 10:
Contents List of Figures List of Ta
Page 11:
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 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
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 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
3.3 Numerical Study of the Fluid Dy
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
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
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 210 and 211: 5 Results Flame stand-off ratio ζ
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 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
Page 261 and 262: REFERENCES [20] K. Annamalai and W.
Page 263 and 264: REFERENCES [39] C.H. Beck, R. Koch,
Page 265 and 266: REFERENCES [60] F. Buda, R. Bounace
Page 267 and 268: REFERENCES [80] Comsol AB (Stockhol
Page 269 and 270:
REFERENCES [102] D.L. Dietrich, P.M
Page 271 and 272:
REFERENCES [124] R. Ennetta, M. Ham
Page 273 and 274:
REFERENCES [146] A.G. Gaydon and H.
Page 275 and 276:
REFERENCES [167] M.P. Halstead, L.J
Page 277 and 278:
REFERENCES [187] K.J. Hughes, T. Tu
Page 279 and 280:
REFERENCES [207] M. Kikuchi, N. Sug
Page 281 and 282:
REFERENCES [229] N.M. Laurendeau. F
Page 283 and 284:
REFERENCES [253] A. Liñán and F.A
Page 285 and 286:
REFERENCES [273] R.D. Matthews, R.F
Page 287 and 288:
REFERENCES [293] K.G. Moesl, T. Sat
Page 289 and 290:
REFERENCES [312] V. Nayagam, J.B. H
Page 291 and 292:
REFERENCES [333] PCB Piezotronics,
Page 293 and 294:
REFERENCES [353] K.K. Rink and A.H.
Page 295 and 296:
REFERENCES [374] T. Sano. NO 2 Form
Page 297 and 298:
REFERENCES [395] A.T. Shih and C.M.
Page 299 and 300:
REFERENCES [419] J.H. Spurk. Ström
Page 301 and 302:
REFERENCES [441] J.S. Tsai and A.M.
Page 303 and 304:
REFERENCES [462] S.-C. Wong, A.-C.
show all

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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?