Study On The Early Combustion Characteristics Of Overloaded Wire Insulation In Weak Buoyancy Environment

With the continuous development of China manned space program, fire safety of the manned spacecraft attracts more and more attention of the country. There are two of the three elements of fire, including oxidizer (essential oxygen for astronauts) and potential ignition source (electronic components), which can’t be removed in manned spacecraft. The only possible element which can be eliminated is combustible (non-metallic material). Wire insulation is a kind of typical non-metallic material and it exists everywhere inside the spacecraft. In addition, overload or short circuit of wire, is also one of the main potential ignition source. So the research of wire insulation combustion characteristics in microgravity condition is crucial. Due to the fact that duration of microgravity condition in foundation facilities is too short to overload wire, which can’t meet the needs of the experiment. Although microgravity condition can be maintained for a long time in space facilities, the cost of experimenting in space facilities is too high, and the opportunity is too scarce.According to the Functional Simulation Method (FSM) and the Narrow Channel Simulation Method (NCSM), the early combustion characteristics of polyethylene (PE) wire insulation in weak buoyancy environment is simulated through the ground laboratory system. In this thesis, the early combustion characteristics refer to not only the smoke emission process and the temperature characteristic before the insulation ignited, but also the flame shape variation, ignition delay time, and the minimum ignition current when the insulation catch fire.In chapter 2, the FSM is used to study the effect of oxygen concentration and pressure on the smoke emission characteristic of insulation under low pressure. Results show that when the pressure is lower than 10 kPa, pressure is the main factors to affect the smoke emission characteristics. And with the decrease of pressure, the rate of insulation’s reaction and temperature rising become faster, but because of the oxygen being reduced, the amount of smoke will also be lowered accordingly.In chapter 3, the early combustion characteristics of wire insulation in narrow channel in atmospheric environment is investigated. It turns out that with the increase of narrow channel height, the combustion duration and the combustion intensity increase rapidly. It has a better effect on the simulation of weak buoyancy environment when the height of the horizontal narrow channel is 10mm. The material of the narrow channel has a remarkable influence on insulation’s smoke emission process and its temperature rising rate.In chapter 4, in order to simulate very weak buoyancy environment, the FSM and the NCSM are combined, called the Low Pressure Narrow Channel Simulation Method (LPNCSM). Results obtaining through the LPNCSM indicate that in the smoke emission process of insulation, the peak of insulation’s temperature and temperature rising rate are well above the NCSM. It shows that the increase of buoyancy level obviously enhances the accumulation of heat, which makes the ignition of insulation possible. Beyond that, the LPNCSM is more conducive to study the early combustion characteristics of wire insulation than the FSM for horizontal wire insulation, because the LPNCSM can delay the fall of insulation from the wire.In conclusion, comprehensive investigation has been made to simulate the early combustion characteristics of wire insulation in weak buoyancy environment. It provides certain reference for the qualitatively study of ignition characteristics of nonmetal material in microgravity condition.