郭景宗臺灣大學：機械工程學研究所許智倫Hsi, Chih-LunChih-LunHsi2007-11-282018-06-282007-11-282018-06-282004http://ntur.lib.ntu.edu.tw//handle/246246/61459本研究主要係選用花梨木、橡木及松木三種木材，以實驗方式研究單一木球在高溫氣流中受熱起燃與燃燒之現象。木球於實驗前先經烘乾程序，於加熱實驗時將木紋方向控制為與氣流垂直及水平兩種情況，並以不同的空氣溫度及流量進行加熱實驗。部分實驗則以熱偶計量測木球內部溫度分布。實驗結果顯示，以673 K及773 K之空氣加熱時，木球表面會先產生熾熱氧化反應後，再產生火焰起燃；反之，以873 K之空氣加熱時，於較短時間內木球表面尚未產生熾熱氧化反應前，即先產生火焰起燃現象，且起燃時間不受空氣流量或木紋方向所影響。本研究提出火焰起燃時間與加熱條件之關係式，並以理論模式計算木球在產生火焰起燃前之質量及溫度。由元素分析結果顯示，於火焰燃燒階段中，木球成分H/O比值維持於一定的範圍內。此外本研究並以理論模式計算木球於火焰燃燒階段時的質量變化。The ignition and combustion behavior of single wood spheres heated in high temperature air streams was investigated by experiments. Three species of wood were used for experiment in this work. The single wood spheres were oven-dried and exposed to various temperature and flow rate of air streams. Wood grain orientation was specifically kept perpendicular or parallel to the air stream. Some tests for measuring the variations of wood sphere internal temperatures were conducted by thermocouples imbedded in the wood spheres. It was observed that the ignition time is independent on air flow rates or grain orientation at 873 K. Glowing reaction was observed prior to ignition for wood heated at 773 K, and directly flaming ignition for 873 K. A correlation for estimating the time required to flaming ignition was proposed. A simple model considering the heats of pyrolysis and moisture evaporation was used to predict the mass and temperature histories prior to flaming ignition. Elemental composition analysis shows that the atomic ratio of H and O of the internal material of burning wood spheres are essentially within a close range during flaming combustion. Shrinking core model was used for estimating the burning rate of wood spheres. Char combustion rate was also discussed in this study.ABSTRACT (in Chinese)…………………………………………I ABSTRACT…………………………………………………………II CONTENTS…………………………………………………………III LIST OF FIGURES…………………………………………………VI LIST OF TABLES…………………………………………………XI NOMENCLATURE………………………………………………….XII CHAPTER 1 INTRODUCTUON……………………………………….1 1.1 Physical and Chemical Phenomenon of Wood Combustion..1 1.1.1 Heat-up and drying…………………………………………1 1.1.2 Thermal decomposition……………………………………2 1.1.3 Ignition and combustion…………………………………4 1.2 Literature review……………………………………………6 1.2.1 Previous work on pyrolysis and thermal decomposition of wood……………………………………………………….6 1.2.2 Previous work related to ignition of wood…………8 1.3 Overview of this Study………………………………...10 CHAPTER 2 EXPERIMENTAL……………………………………….12 2.1Facility……………………………………………………12 2.2Materials…………………………………………………….13 2.3 Test Conditions………………………………………15 2.4 Procedure of Tests…………………………………17 CHAPTER 3 IGNITION………………………………………………19 3.1 Prior to Flaming Ignition…………………………………19 3.2 Characteristics of Flaming Ignition…………………………….26 3.2.1 Time to flaming ignition…………………………………26 3.2.2 Correlation of ignition time……………………………29 3.2.3 Ignition Temperature…………………………………….32 3.2.4 Mass Flux at Ignition…………………………………….34 3.2.5 Modes of ignition………………………………………..37 3.3Pyrolysis Model…………………………………………….….40 3.3.1 Previous work……………………………………………40 3.3.2 Mathematical formulation…………………………….…43 3.3.3 Material properties and kinetic parameters……………...46 3.3.4 Dimensionless form of pyrolysis model………………....47 3.3.5 Results and discussion of pyrolysis model……………....49 3.3.5.1 Wood spheres heated at 773 K……………….…....49 3.3.5.2 Wood spheres heated at 873 K………….58 CHAPTER 4 FLAMING AND CHAR COMBUSTION………………65 4.1 Experimental Observations………………………………….…65 4.2 Fuel Analysis………………………………………….71 4.3 Mass Loss History……………………………………77 4.3.1 Mass loss during flaming combustion stage……77 4.3.2 Mass loss during char combustion stage…………85 4.4 Temperature and Core Front Propagation……………86 CHAPTER 5 CONCLUSIONS…………………………………………99 5.1 Ignition…………………………………………99 5.2 Flaming and Char Combustion………………102 REFERENCES………………………………………………………104 APPENDIX A MASS HISTORIES OF WOOD SPHERES HEATED IN HIGH TEMPERATURE AIR STREAMS…………….110 APPENDIX B DATA OF FUEL ANALYSIS IN SECTION 4.2……1162330187 bytesapplication/pdfen-US起燃木材熱解燃燒pyrolysiswoodcombustionignitionthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/61459/1/ntu-93-D84522005-1.pdf