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The work reported addresses metal ignition from the possible rubbing of oxygen pressurized hydrostatic bearings and turbine blade tips operating in a high-pressure oxygen environment. Friction heating tests in oxygen at pressures of 1 to 300 atm were conducted at surface speeds of 10 to 33 m/s. Materials selections were based on their burn factor (heat of combustion/thermal diffusivity). Test results presented include the rubbing of like material pairs spanning a wide range of burn factors and dissimilar metal pairs having significantly different burn factors. The test results indicated that the burn factor can provide a useful guide for selecting metals for use in oxygen where rubbing can occur. The burn factor is suitable for rank ordering most, but not all, materials in their resistance to ignition. Most materials became more difficult to ignite under the high-speed rubbing test conditions when the oxygen pressure increased from 60 to 300 atm. However once they ignited, the burning was more extensive. A mechanism that explains these observations and thermal instabilities as evidenced by self-induced heating and cooling cycles under linearly increasing rubbing loads is postulated. It is supported by experimental data.
flammability, metal ignition, high pressure oxygen, friction heating tests
Scientist, Aerojet TechSystems Co., Sacramento, CA
Project leader, NASA-JSC White Sands Test Facility, Las Cruces, NM
Project Manager, NASA Lewis Research Center, Cleveland, OH