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Thursday, May 18, 2006 - 10:00 AM
EMP064.5

Rolling Element Bearing Performance in Jet Fuel vs. Turbine Oil

T. Y. Hui, F. Sadeghi, Purdue University, West Lafayette, IN; R. G. Rateick Jr., Honeywell Aerospace, South Bend, IN

Jet fuel, designed primarily to burn, is not commonly thought of as a good lubricant, yet many existing and emerging aerospace propulsion system component designs rely on the fuel to lubricate things such as rolling element bearings.  However, compared with oil, little data exists for bearing life and performance prediction in jet fuel.  This research compares the rolling contact fatigue behavior of metal (AISI 52100 on M50) bearing couples and silicon nitride (NBD-200) on metal (M50 and BG42) hybrid bearing couples in fuel (JP8+100) and turbine oil (MIL-PRF-23699).  Additional results show the running torque and thermal behavior for tapered roller bearings and angular contact ball bearings in fuel and oil lubricants and the friction coefficient of fuel under various loads and slide to roll ratios.

Weibull analysis of rolling contact fatigue results showed lives of hybrid bearings in fuel were not as good as in oil, as would be expected.  The lower viscosity and the attendant reduction in film thickness give rise to higher stresses in the fuel vs. oil lubricated bearings.  The torque and thermal characteristics of bearings operating in fuel vs. oil show that in general, the fuel lubricated bearings run significantly cooler and with less parasitic torque.  This is thought to be largely the result of the lower viscosity.  The friction coefficient of fuel is also similar in magnitude to other oils.

Thus, fuel is not as poor of a bearing lubricant as might be expected.  Rolling contact fatigue resistance is not as good as in oil, but the reduced parasitic bearing torque losses in fuel contribute to greater component operating efficiency and incrementally reduced weight.  Also, lower operating temperatures for the fuel lubricated bearing may allow use of lighter weight structural materials for the housings.


Summary: Little data exists in the literature for life prediction for steel or steel/ceramic hybrid rolling element bearings operating in jet fuel. This presentation will compare rolling contact fatigue, torque, and thermal performance data for aerospace bearings operating in jet fuel and turbine oil.