PYROLYSIS AND COMBUSTION PROCESSES OF COMBUSTIBLE MATERIALS UNDER EXTERNAL HEAT FLUX LONG SHI NATIONAL UNIVERSITY OF SINGAPORE 2014 PYROLYSIS AND COMBUSTION PROCESSES OF COMBUSTIBLE MATERIALS UNDER EXTERNAL HEAT FLUX LONG SHI (M.ENG., USTC) (B.ENG., FZU) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF BUILDING NATIONAL UNIVERSITY OF SINGAPORE 2014 Acknowledgement I would like to thank my supervisor, Professor Michael Yit Lin Chew, for giving me the opportunity to join his research group. And I am very grateful for his valuable guidance and encouragement throughout my PhD study. I am also thankful to the rest of Thesis Committee, Professor Wong Nyuk Hien and Dr. Lim Guan Tiong, for their help on the improvement of this thesis. I would like to thank Seah Kai Wei and Lionel Chong for their assistance on conducting experiments. We will never forget the time of running between laboratory and canteen to save some time for more experimental runs. And help from Mr. Zaini Bin Wahid on laboratory supports are appreciated. Dozens of people have helped and taught me not just on research. Thank Dr. de Ris (FM Global, USA) for the discussion on transportation and evaporation of liquid water inside solid slab. I appreciate Professor Su Chang (Department of Mechanical Engineering, National University of Singapore, Singapore) for his suggestions on solving non-linear PDEs. Professor Richard Yuen (City University of Hong Kong, Hong Kong) shared his experience without any reserve about boundary conditions of gas phase. Thank Dr. Linteris (National Institute of Standard and Technology, USA) for the discussion about flame and volume change of wood samples. Thank Professor Jake Blanchard (University of Wisconsin, Madison, USA) for his selfless help on solving PDEs and program optimization. I must thank Dr. Wang Junhong (High Performance Center, National University of Singapore, Singapore) for his help about running jobs efficiently on HPC platform. The main contents of this thesis have been published in journals and conference proceedings. I would like to thank anonymous reviewers from Fire Safety Journal, Fuel, Journal of Fire Sciences, Journal of Thermal Analysis -ii- and Calorimetry, and Technical Committee of the 9th Asia-Oceania Symposium on Fire Science and Technology, etc. Their comments and suggestions mean a lot to this thesis. This thesis cannot be done without the supports from my family. Thank my wife Xiaofang Xu for her priceless encouragement and supports. I never forget her figure under yellow lights when she brought me umbrella and waited for me at bus stop on the raining night. Thank my parents, Zhitang Shi and Yumei Hu, for their unconditional supports. This study was supported by Research Project (R-296-000-135-112) funded by the Ministry of Education, Singapore. Also I would like to acknowledge the award of NUS Research Scholarship from University Research Office. -iii- Table of content Abstract x List of Tables xiii List of Figures xv Nomenclature xxi Chapter 1: Introduction 1.1 Introduction . 1.2 Research gaps 1.2.1 Fire behaviors under autoignition conditions . 1.2.2 Fire behavior modeling of different types of combustible materials under autoignition conditions 1.2.3 Combustion processes of gas volatiles in gas phase . 1.3 Research objectives and significances 11 1.4 Scope of work . 12 Chapter 2: Literature review 16 2.1 Introduction . 16 2.2 Fire processes 16 2.2.1 Thermal processes . 17 2.2.2 Chemical processes . 19 2.2.2.1 Pyrolysis reaction 19 2.2.2.2 Production of gas volatiles 22 2.2.2.3 Combustion of volatiles 24 2.2.3 Physical processes . 26 2.2.3.1 Transportation of gas volatiles 26 2.2.3.2 Thermal shrinkage . 27 2.2.3.3 Permeability 30 2.2.3.4 Water evaporation . 34 2.2.3.5 Thermal expansion 36 2.2.3.6 Porosity . 39 -iv- 2.2.4 Failure processes . 40 2.3 Previous models for combustible materials 42 2.3.1 Wood . 42 2.3.2 Non-charring polymers . 43 2.3.3 Charring polymers 44 2.3.4 Intumescent polymers . 45 2.3.5 A summary of previous models . 46 2.4 Concluding remarks 48 Chapter 3: Mathematical formulation of FiresCone and its solution methodology 50 3.1 Introduction . 50 3.2 Mathematical model 50 3.2.1 Governing equations . 50 3.2.2 Thermal processes . 53 3.2.3 Chemical processes . 55 3.2.4 Physical processes . 56 3.2.4.1 Transportation process of gases and liquids 56 3.2.4.2 Volume change 57 3.2.5 Thermal properties 57 3.2.6 Initial and boundary conditions 57 3.3 Solution methodology . 59 3.3.1 Program structure of FiresCone 59 3.3.2 Discretization 61 3.3.3 Pressure-velocity coupling 65 3.3.4 Solution of governing equations . 65 3.4 Concluding remarks 71 Chapter 4: Fire behaviors of wood under autoignition conditions 72 4.1 Introduction . 72 4.2 Experimental design and methodology . 72 -v- 4.2.1 Materials . 72 4.2.2 Apparatus 73 4.2.3 Procedure 73 4.2.4 Repeatability . 74 4.3 Wood under ambient environment 75 4.3.1 Ignition time and ignition temperature . 75 4.3.2 Mass loss rate 81 4.3.3 CO release rate 86 4.3.4 CO yield 89 4.4 Influences of moisture content 93 4.4.1 Ignition time and ignition temperature . 93 4.4.2 Mass loss rate 100 4.4.3 CO release rate 102 4.4.4 CO yield 104 4.5 Concluding remarks 107 Chapter 5: Fire behaviors of polymers under autoignition conditions 110 5.1 Introduction . 110 5.2 Experimental design and methodology . 110 5.3 Analysis of raw data 111 5.4 Comparisons between charring and non-charring polymers 112 5.5 Autoignition time and thermal thickness 116 5.6 Heat release characteristics . 121 5.6.1 Heat release rate 121 5.6.2 Heat of combustion . 122 5.7 Mass loss rate 124 5.8 Gas release rate and gas yield . 127 5.8.1 Gas yields under non-flaming and flaming conditions . 127 5.8.2 Gas yields under autoignition and piloted ignition conditions130 5.8.3 Influences of heat flux to gas yields . 131 -vi- 5.8.4 Influences of mass percent of carbon to gas yields . 132 5.9 Concluding remarks 135 Chapter 6: Sensitivity analysis of FiresCone . 138 6.1 Introduction . 138 6.2 Sensitivity analysis of input parameters . 138 6.2.1 Grid spacing 138 6.2.2 Time step . 140 6.2.3 Heat of reaction . 142 6.2.4 Pre-exponential factor . 143 6.2.5 Activation energy 145 6.2.6 Thermal conductivity 147 6.2.7 Specific heat capacity . 149 6.2.8 Density 150 6.2.9 Heat transfer coefficient 152 6.2.10 Water permeability 153 6.2.11 Char yield 154 6.2.12 Diffusion coefficient of water . 156 6.2.13 Surface emissivity and absorptivity 156 6.2.14 Moisture content . 158 6.3 Concluding remarks 160 Chapter 7: Validation and application of FiresCone 162 7.1 Introduction . 162 7.2 Modeling results of wood . 162 7.2.1 Thermal properties of Cherry 162 7.2.2 Mass loss rate 165 7.2.3 Temperatures inside solid phase . 169 7.2.4 Temperature and gas velocity in gas phase . 172 7.2.5 Gas volatiles in gas phase . 175 7.3 Modeling results of non-charring polymers 179 -vii- 7.3.1 Thermal properties of PMMA . 179 7.3.2 Mass loss rate 181 7.3.3 Temperatures inside sold phase . 185 7.3.4 Temperature and gas velocity in gas phase . 189 7.3.5 Gas volatiles in gas phase . 191 7.4 Modeling results of charring polymers . 194 7.4.1 Thermal properties of ABS . 194 7.4.2 Mass loss rate 196 7.4.3 Temperatures inside solid phase . 201 7.4.4 Temperature and gas velocity in gas phase . 203 7.4.5 Gas volatiles in gas phase . 203 7.5 Modeling results of intumescent polymers . 208 7.5.1 Thermal properties of PC 208 7.5.2 Mass loss rate 209 7.5.3 Temperatures inside solid phase . 212 7.5.4 Temperature and gas velocity in gas phase . 215 7.5.5 Gas volatiles in gas phase . 216 7.6 Concluding remarks 218 Chapter 8: Conclusions and future work . 220 8.1 Overview of work done 220 8.2 Conclusions and recommendations . 221 8.2.1 Wood under autoignition conditions . 221 8.2.2 Polymers under autoignition conditions . 223 8.2.3 Mathematical model of FiresCone 224 8.2.3.1 Sensitivity analysis of FiresCone 224 8.2.3.2 Validation and application of FiresCone . 226 8.3 Major contributions . 227 8.3.1 Theoretical contributions 227 8.3.2 Practical contributions 228 -viii- 8.4 Limitation and future work . 228 References 230 Appendix A: A summary of kinetic data of different types of combustible materials . 258 Appendix B: A summary of considerations in previous one-dimensional models for wood 265 Appendix C: A summary of considerations in previous one-dimensional models for non-charring polymers . 270 Appendix D: A summary of considerations in previous one-dimensional models for charring polymers 272 Appendix E: A summary of considerations in previous one-dimensional models for intumescent polymers 273 Appendix F: Experimental photos . 275 Appendix G: Main code of FSOLID . 278 Appendix H: Main code of FGAS . 288 Appendix I: Peer-reviewed publications during PhD study . 295 -ix- [...]... heat flux 43 2.4 Main fire processes of non-charring polymers under external heat flux 44 2.5 Main fire processes of charring polymers under external heat flux 45 2.6 Main fire processes of intumescent polymers under external heat flux 46 3.1 Schematic of combustible material under extern heat flux 52 3.2 Computational domain in FiresCone 53 3.3 Structure of program 60 3.4 Grids... combustion processes of combustible materials under external heat flux FiresCone is capable of simulating fire behaviors of combustible materials in both solid and gas phases The generality of FiresCone allows fire professionals and materials formulators to simulate pyrolysis and combustion processes of four types of combustible materials, including wood, non-charring, charring and intumescent polymers FiresCone... 123 5.5 MLR history under external heat flux 126 5.6 Comparisons of average MLR under different heat flux 128 5.7 Comparisons of gas yields under 50 and 75 kW/m2 133 5.8 Comparison of yCO/yCO2 under heat flux 134 -xvi- 5.9 Comparisons of gas yields under different situations 135 6.1 Influence of grid spacing on surface temperature 139 6.2 Influence of grid spacing on mass... modeling and experiments for PMMA under 50 kW/m2 heat flux 184 7.18 Comparisons between modeling and experiments for PMMA under 75 kW/m2 heat flux 185 7.19 Temperatures inside PMMA slabs under 25 kW/m2 heat flux 186 7.20 Temperatures inside PMMA slabs under 50 kW/m2 heat flux 187 -xviii- 7.21 Temperatures inside PMMA slabs under 75 kW/m2 heat flux 188 7.22 Temperature and gas... modeling and experiments for ABS under 75 kW/m2 heat flux 199 7.34 Temperatures inside ABS slabs under 25 kW/m2 heat flux 200 7.35 Temperatures inside ABS slabs under 50 kW/m2 heat flux 201 7.36 Temperatures inside ABS slabs under 75 kW/m2 heat flux 202 7.37 Temperature and gas velocity in gas phase for 10 mm thickness ABS under 25 kW/m2 heat flux 203 7.38 Temperature and gas... through shrinkage under external heat flux, but PVC and PC undergo expansion [3-5] Intumescent polymers are capable of forming a volumetric carbonized residue which protects surface of polymers under external heat flux This volumetric carbonize residue go through expansion because of melted polymer matrix and large amount of upward gas volatiles Table 1.1 A classification of combustible materials in buildings... PP, etc PC, PVC, etc These four types of combustible materials show various fire behaviors under external heat flux As very important tool in fire risk evaluation, numerical method must be capable of simulating fire behaviors of different types of combustible materials Because of various fire behaviors of these four types of combustible materials, it is challenging and significant in numerical modeling... single type of combustible materials, resulting in a lack of overview for different types of combustible materials Investigation of pyrolysis and combustion processes of combustible materials is critical to fire risk evaluation 1.2 Research gaps Besides piloted ignition, autoignition is also an important aspect to real fire development as combustible materials can be ignited by internal heating, without... ABS under 50 kW/m2 heat flux 204 7.39 Temperature and gas velocity in gas phase for 10 mm thickness ABS under 75 kW/m2 heat flux 204 7.40 Mass fraction of O2 (left half) and Fuel (right half) in gas phase for 10 -xix- mm thickness ABS under 25 kW/m2 heat flux 205 7.41 Mass fraction of O2 (left half) and Fuel (right half) in gas phase for 10 mm thickness ABS under 50 kW/m2 heat flux. .. half) and CO (right half) in gas phase for 10 mm thickness ABS under 75 kW/m2 heat flux 207 7.46 Comparisons between modeling and experiments for PC under 50 kW/m2 heat flux 211 7.47 Comparisons between modeling and experiments for PC under 75 kW/m2 heat flux 212 7.48 Temperatures inside PC slabs under 50 kW/m2 heat flux 213 7.49 Temperatures inside PC slabs under 75 kW/m2 heat . non-charring polymers under external heat flux 44 2.5 Main fire processes of charring polymers under external heat flux 45 2.6 Main fire processes of intumescent polymers under external heat flux 46 3.1. PYROLYSIS AND COMBUSTION PROCESSES OF COMBUSTIBLE MATERIALS UNDER EXTERNAL HEAT FLUX LONG SHI NATIONAL UNIVERSITY OF SINGAPORE 2014 PYROLYSIS AND COMBUSTION. combustion processes of combustible materials under external heat flux. FiresCone is capable of simulating fire behaviors of combustible materials in both solid and gas phases. The generality of FiresCone