The Effect of Switch-Loading Fuels on Fuel-Wetted Elastomers 2007-01-1453

The Office of the Secretary of the Defense (OSD), Advanced Systems and Concepts, established the OSD Assured Fuels Initiative, which aims to spark commercial production of clean fuels made from U.S. energy sources for use by the U.S. Military. The Department of Defense (DoD) will provide the “spark” by developing the fuel specifications needed, demonstrating and qualifying the use of these fuels in tactical ground vehicles, aircraft, and ships, and transitioning to the full-time use of these fuels in their fleets operating in the U.S. One such clean fuel, Fischer-Tropsch (FT) synthetic fuel, made using low-temperature FT technology, contains no aromatic compounds. This lack of aromatics, along with the lack of sulfur, are the key differences between a FT kerosene-based fuel and the petroleum-derived JP-8/JP-5 kerosene-based fuel that is the predominate bulk fuel used by the military's air, ground, and marine fleets. [1, 2]¹ A series of experiments were done to determine effects to the fuel-wetted elastomers typically found in sealing applications throughout various fuel distribution systems of DoD equipment, to switching between fuel containing aromatics to fuel with no aromatics, a.k.a. “switch-loading”. One grade of nitrile studied exhibited large dimensional swings, as much as 8% volume change, upon fuel switch-loading. Such dimensional change presents potential for fuel leakage around the seals; this is especially true for older O-rings or gaskets that have taken a compression set. When transitioning to the use of FT fuels in DoD fleets, this risk of fuel leakage can be mitigated through the use of blends of FT kerosene with JP-8 or through identifying susceptible sealing applications and replacing the elastomer components therein with new components and/or components made of less affected, more suitable elastomers.