Study On External Characteristics Of Smoldering In Confined Space In Low Pressure

Aircraft cargo compartment fire has always been one of the main factors threatening the safety of civil aviation transportation.Due to the change of air pressure in the cargo compartment during the flight and takeoff and landing of the aircraft,the concentration of particulate matter in the cargo compartment will change,so that the smoke detector will produce false alarm.Moreover,the variety of cargo in the cargo compartment will affect the accurate alarm,so the high false alarm rate of cargo compartment fire is the major problem.In addition,there are many high altitude airports in China.The development law of fire in low pressure and low oxygen environment is very different from that in plain areas,which has become a great challenge in the process of fire rescue and personnel escape.Smoldering occurs in the initial stage of fire development,and only smoke without fire.If the fire smoldering stage can be detected very early and the fire extinguishing system can be started,the accident will not occur.Therefore,it is of great significance to study the smoldering characteristics under low pressure,which can provide a certain reference for the research and development of the new generation aircraft cargo compartment fire extinguishing system and the fire prevention code of high altitude airports.The Sichuan Provincial Key Laboratory of civil aircraft fire science and safety engineering with an altitude of 460 m and a pressure of 96 k Pa and the high altitude Aviation Safety Laboratory of Kangding airport with an altitude of 4260 m and a pressure of 61 k Pa were selected as the experimental sites.The smoldering experiments of three materials were carried out under normal and low pressure with corrugated cardboard,cotton rope and beech as experimental materials at three heating temperatures（400,500 and 600℃）,The effects of air pressure and heating temperature in the confined space on the surface temperature,smoke component concentration,smoke particle concentration and smoke particle velocity during smoldering were studied.The results show that the peak temperature of the three materials increases with the increase of heating temperature,and the maximum value is 592.15℃of corrugated board.Under the same heating temperature,the peak temperature of beech is higher at 61 k Pa and the peak time is longer at 96 k Pa.The CO concentration of corrugated board is the highest at both pressures,up to 158 ppm at 400℃and 61 k Pa,and the time to reach the peak at 400℃and 96 k Pa is the shortest,taking only 654 s,indicating that the fire risk of corrugated board is greater,and the fire safety at low pressure should be paid more attention to.The CO peak time of the three materials showed different rules,and the time of beech was the longest.The CO₂and O₂ concentrations of materials do not change significantly under different conditions,so the co parameters should be paid more attention to in the very early fire detection;The mass concentration of smoke particles produced by smoldering is higher at low pressure.The mass concentration of smoke particles of the same material at two pressures increases with the increase of heating temperature.For different materials with the same mass,the mass concentration of smoke particles depends on the type of material.Cotton rope is the highest,corrugated cardboard is the second,and beech is the lowest;For the velocity of smoke particles,the velocity at low pressure is generally higher than that under normal pressure,and the increment is about 0.101 m/s.At the same pressure,changing the heating temperature has little effect on the velocity of smoke particles;The speed of smoke particles depends on the type of material.The speed of beech is the highest,followed by corrugated paperboard,and the speed of cotton rope is the lowest.This law can provide guidance and basis for the design and use of air sampling fire detector.