The Effect of Switch-Loading Fuels on Fuel-Wetted Elastomers

Abstract

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...

Propulsion and Power Rapid Response Research and Development (R&D) Support. Delivery Order 0011: Analysis of Synthetic Aviation Fuels

“…This is the only neat fuel in the set and contains no aromatics. The relationship between increased aromatic content and increased volume swell (especially with nitrile) has been well-documented by others 5 . In this case, the 50/50 blends in the study all contain approximately 10% aromatics and exhibit similar behavior.…”

Alternative Microturbine Fuels Feasibility Study Through Thermal Stability, Material Compatibility, and Engine Testing

“…The internal diameter measures 53 mm and the width is 5 mm. The material was selected for two reasons: It is representative of the types of elastomer materials found in turbine fuel systems [15] and it is sensitive to changes in fuel aromatic species content, especially compared to fluorinated carbon polymers [15][16][17]. Two O-ring samples were placed in glass beakers, each containing a different fuel type at ambient temperature.…”

US Army Qualification of Alternative Fuels Specified in MIL-DTL-83133H for Ground Systems Use. Final Qualification Report: JP-8 Containing Synthetic Paraffinic Kerosene Manufactured Via Fischer-Tropsch Synthesis or Hydroprocessed Esters and Fatty Acids

“…These protocols are referenced in the reports and papers on fuel evaluations for SPK (FT and HEFA) and the blends of SPK with JP-8 (or near equivalents JP-5, Jet A-1 and Jet A), of which only a small fraction are cited herein. (11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33) BASIC AND SPECIFICATION PROPERTIES…”