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Clean, very low sulfur fuels produced from domestic resources are of interest to the U.S. Military to enhance supply security and reliability versus continuing to rely on the supply of fuels that are either manufactured from an increasing percentage of imported oil or imported in increasing amounts as finished products. [1] * Synthetic Fischer-Tropsch (FT) fuel is one type of fuel that can be produced from domestic resources. FT fuels can be produced from a variety of non-petroleum feed stocks, such as natural gas, coal, petroleum coke, or even biomass and various wastes. Starting with reforming or gasification processes, the FT technology first produces synthesis gas (syngas) which is subsequently processed to high-boiling hydrocarbons. These hydrocarbons are then hydrocracked, hydroisomerized, and/or hydroprocessed to produce the desired liquid fuels. The military has a Single Battlefield Fuel Policy which mandates use of the JP-8/JP-5/Jet A-1 aviation turbine fuels. These are currently derived from conventional resources such as petroleum (crude oil). FT aviation turbine fuels have been produced and are being evaluated for use in military equipment by a Joint Agency Department of Defense (DoD) and Department of Energy (DoE) Team. The military will most likely utilize blends of FT fuels with petroleum JP-8/JP-5/Jet A-1 as a first step in evolving towards the use of cleaner fuels that can be produced from domestic resources. Properties of these "FT/petroleum fuel blends" are shown to be similar to those of petroleum JP-8/JP-5/Jet A-1. * Numbers in brackets refer to references.

When some elastomer (rubber) compounds, and specifically those used for seals in fuel-wetted components of vehicles and equipment, are suddenly "switch-loaded" from a fuel of given composition to one of a somewhat different composition, swell/shrink issues relating to seal performance may arise, possibly leading to fuel leakage. The key objective of this study was to evaluate what happens to the elastomers with sudden switches from a conventional (petroleum-derived) fuel to a synthetic (non-aromatic) paraffinic fuel produced from natural gas using gas-to-liquids (GTL) and Fischer-Tropsch (FT) synthesis processes with or without surrogate aromatics. Results from this evaluation indicate that, for the nitrile elastomers evaluated, relatively large swings in swell occur with switches between fuels of varying levels of aromatic content and the synthetic aviation turbine fuel containing no aromatics. These observations support the conclusion that impact on the nitrile elastomer when switch-loading synthetic (non-aromatic) and petroleum-derived fuel, is highly dependent on aromatic hydrocarbon type and concentration. EXECUTIVE SUMMARY Problems and Objectives Issues with seal performance may arise and possibly lead to fuel leakage when some elastomer (rubber) compounds, particularly those used for seals in liquid fuel-wetted components of vehicles and equipment, are suddenly "switch-loaded" from one kind of fuel to another. Evaluating how these elastomers respond as they are switched back-and-forth between two fuels of different compositions is a key area of study. This type of study is needed to identify potential performance issues that may arise when such fuel switches occur. The overall objective of this study was to simulate how elastomers, found in fuel-wetted components of Army ground and combat vehicles, may respond when switching fuels. In particular, this study evaluates what happens to the elastomers with sudden switches from a conventional or petroleum-derived type of fuel to a synthetic (non aromatic) paraffinic fuel produced from natural gas using gas-to-liquids (GTL) and Fischer-Tropsch (F-T) synthesis processes with or without surrogate aromatics. Studies conducted in 2003 indicate that nitrile elastomers may be particularly sensitive to changes as they are exposed to fuels and that the magnitude and direction of these changes is also dependent on the aromatic content of the fuel. Importance of Project This study was completed under a joint DoD-DoE Memorandum of Agreement (MOA) to conduct collaborative research and development in the assessment of alternative fuels, particularly synthetic military fuel produced from GTL and F-T technology. This project is one of several second year efforts under this MOA to address the potential use of F-T fuels by the military. Technical Approach To assess the response of selected elastomers to switches between fuel pairs, coupons and O-rings of the selected elastomer were immersed in the first fuel of each fuel pair and remained there, at 40°C temperature, for a perio...

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