Study On Combustion Properties Of Aviation Cable Materials Under Low Ambient Pressure

This dissertation is closely related to the scientific problems of aviation cable thermal safety in the low pressure in flight.The combustion experiments were conducted in the high-altitude aviation safety laboratory where the altitude is 4290m and the atmospheric pressure is 61kPa in the Kangding Airport of Sichuan province and also in the Basic technology research base of civil aviation where the altitude is 520m and the air pressure is96kPa in the Guanghan of Sichuan province,and the combustion characteristics of aviation cable materials were contrastive analysis in normal and low pressure environment.The ignition performance of aviation cable materials under different thermal radiation conditions in normal and low pressure environment were carried out,and the factors of ignition time,thermal radiation temperature and combustion form of aviation cable and inner sheath materials were analyzed in comparative experimental research.The comparative analysis of the aviation cable smoke density and smoke composition including CO,CO₂ and O₂ were comparative studied during the experimental study of smoke performance.The experimental study on the heat-resistant performance of aviation cable under different oxygen concentration were carried out,and the combustion duration,combustion speed and mass loss rate of aviation cable and its inner sheath were contrastive analyzed.On the basis of the comparative experiments under normal and low pressure,the combustion characteristics of the aviation cable and its inner sheath coupling were analyzed.In the first,from the analysis of ignition time and radiation temperature of aviation cable materials,when the thermal radiation temperature is between 500℃and 600℃,the thermal resistance of the materials will weaken rapidly,which will lead to increase the fire risk.The influence of pressure on ignition time decreased with the increase of external thermal radiation temperature.The heat resistance of the sheath was worse than that of the insulation,while the heat resistance of the whole cable was stronger than sheath with insulation.The ignition time of aviation cable materials under low pressure was generally longer than the normal pressure.Second,from the analysis of the smoke density and gas concentration of the aviation cable,the smoke density under normal pressure was larger than that under low pressure and the time was longer.Under normal pressure,the O₂ consumed and CO₂ produced by the whole cable and sheath with insulation were higher than that of low pressure,while O₂consumed and CO₂ produced by the sheath and insulation under low pressure were higher than that under normal pressure,and CO content of insulation and the sheath with insulation under normal pressure were higher than that under normal pressure,while the CO content of the sheath and the whole cable under low pressure were higher than that under normal pressure.The smoke density of the insulation was bigger than that of sheath under normal and low pressure,and the smoke density of the sheath with insulation was bigger than that of the whole cable.The O₂ consumed and CO₂ produced by the sheath were less than that of insulation in the two pressure,and O₂ consumed and CO₂ produced by whole cable were less than that of the sheath with insulation.In addition,the curve of CO content fluctuated during the combustion.Third,the mass loss rate and combustion duration were carried out under different oxygen concentration.The mass loss rate under normal pressure was higher than that under low pressure.With the increase of oxygen concentration,the gap of mass loss rate between normal and low pressure environment increased gradually.The mass loss rate of sheath was faster than insulation,and the mass loss rate of the sheath with insulation was faster than whole cable,thus the fire risk of insulation and whole cable were smaller than sheath and the sheath with insulation.In conclusion,this paper considered that when the temperature of thermal radiation exceeds 600℃,the ignition characteristics of aviation cable materials will be weakened by environment pressure.Under normal and low pressure,the smoke density of insulation was bigger than sheath,and the smoke density of sheath with insulation was bigger than that of the whole cable,so the risk of insulation and sheath with insulation layer were relatively bigger.when the oxygen concentration between 30% and 35%,the heat resistance of aviation cable materials descended rapidly.