| In the process of oxygen charging for aircraft oxygen system,the valve head material inside the oxygen charging valve keeps contacting and separating from the valve body,and at the same time,it will generate a lot of static electricity on its surface due to friction with high-speed air flow.Most of the oxygen charging valve heads are polymer insulation materials with high resistivity.After static electricity is generated,the electric charge will quickly accumulate and not easily dissipate.When it accumulates to a certain extent,it will cause discharge.Under the condition of high pressure and pure oxygen,the combustion characteristics of the materials will change,and the oxygen charging valve head is likely to lead to ignition due to electrostatic discharge,which will lead to aircraft explosion.Therefore,in order to effectively prevent and control such accidents,it is necessary to study the ignition characteristics and danger of valve head materials in the oxygen filled environment.In this paper,firstly,several common electrostatic charging mechanisms and discharge types of solid substances are described from the theoretical point of view.Combined with the specific structure and working principle of aircraft oxygen system,the specific causes of explosion accidents caused by electrostatic discharge in the process of oxygen charging are analyzed.Then,based on the way of electric spark ignition,a high-voltage pure oxygen electrostatic discharge ignition experimental system is designed.Nylon 1010 material,which is the same as the accident valve head of a certain aircraft,is selected to study the ignition characteristics under different oxygen pressure.The minimum ignition energy of nylon material in the range of0.1MPa～5MPa is measured in the experiment,the law of the minimum ignition energy affected by different oxygen pressure is explored,and the risk of electrostatic discharge ignition of oxygen charging valve head is analyzed preliminarily.The main conclusions are as follows:(1)In the range of experimental pressure and voltage,the loss rate of discharge energy reaches 60%-95%.The minimum ignition energy of the material is calculated by collecting the voltage and current signals at both ends of the electrode and integrating the whole process of discharge,which effectively improves the test accuracy.(2)In the pressure range of 0.1MPa～5MPa,the minimum ignition energy of nylon decreases rapidly with the increase of air pressure,and it is approximately exponentially decreasing.When the pressure is 5MPa,the ignition energy is only 0.07 m J,which has a very high risk of electrostatic discharge ignition.The research results have certain significance for mechanism analysis,electrostatic protection and relevant improvement of oxygen system fire accidents. |
