| Nowadays,the air transport industry has played a strongly dominant role in driving the economy of high plateau region.Economic activities in high plateau are becoming increasingly frequent and people’s requirements for their working and living environment are also improving.The problem of human hypoxia in highland areas can be effectively solved by artificially enriching the indoor space where people work or live.However,oxygen-enriched environments inevitably bring additional fire hazards,and the exact changes are not yet clear.This thesis investigated the effects of pressure and oxygen concentration on pyrolysis mechanism by conducting pyrolysis experiments by using carton and pine,typical indoor solid materials on Guanghan plain(95 kPa)and Kangding high plateau(61 kPa),respectively.Combined with the self-built low-pressure and oxygen-enriched combustion platform,combustion experiments under different pressures and oxygen concentrations were conducted,and the fire behaviors of solid materials under low-pressure oxygen-enriched environment were systematically analysed,and the fire hazard of carton material was finally comprehensively assessed by analytic hierarchy process.The following conclusions were obtained:1.There is only one weight loss stage in the pyrolysis of cartons under atmospheric and low pressure environments,and two weight loss stages for pine.Relative to atmospheric pressure,the pyrolysis temperature and maximum mass loss temperature of two materials under low pressure were delayed,and the maximum mass loss rate and remaining mass were larger,and the difference between pyrolysis temperature and maximum mass loss temperature of the carton under atmospheric pressure and low pressure became larger as oxygen concentration increased.The best fit was found by comparing the first level of the reaction level model,where the activation energy was lower for carton and pine in low pressure environment,and the activation energy grew with increasing oxygen concentration at both pressures.There is a good"kinetic compensation effect" between the prefactor A and the activation energy E for different pyrolysis stages of two materials.2.A theoretical relationship between pressure and oxygen concentration with mass loss rate is proposed:m " ∝ C1P2nY02,∞n+1+C2P2Y02,∞4,which was obtained by fitting the data of cardboard burning:m " ∝(PY02,∞2)0.67,indicating that convective heat transfer played a dominant role in cardboard fires.And fitting the mass data of vertical downstream fire of pine:m"∝(PY02,∞2)1.84,indicating that radiant heat transfer played a dominant role in pine fires.Finally,the existing fire pressure model was modified by introducing oxygen concentration:m"max/D～-(P2/L3Yo2,∞)0.72.3.In low-pressure environment,as oxygen concentration increases,the shape of carton flame changed from a thin high type to a wide low type,and the color gradually changed from blue-yellow to bright yellow color.The flame length of stable burning stage of pine tended to grow,and the width tended to increase with increase of pressure and oxygen concentration.Under low pressure,the oxygen concentration had a greater effect on heat production characteristics,and the radiative heat flux of carton fire was proportional to pressure and oxygen concentration.Under high oxygen concentration,the pressure was weakly correlated with the mass loss,ignition time and heat production characteristics,and the oxygen enrichment obviously weaken the inhibitory effect of low pressure on material combustion.4.As the pressure and oxygen concentration increase,the total score derived from the hierarchical analysis becomes larger.With the total score increasing by 135.37 as the pressure increased from 50 kPa to 70 kPa when oxygen concentration was 21%,and the difference in the total score increasing to 153.75 as oxygen concentration increased to 33%.Although low pressure will weaken the fire hazard,by enriching the room with oxygen can equivalently increase the pressure and make the fire hazard increase. |
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