Concerns about the future availability, security, price, and environmental impact of petroleum fuels have increased the interest of the United States Navy, and the United States Department of Defense in general, in developing drop-in alternative fuels produced from sources other than petroleum. These drop-in fuels must be used interchangeably with petroleum fuels and used without modification or replacement of existing materials or infrastructure. One area of concern is the compatibility of alternative fuels with the numerous polymeric materials used in modern fuel systems. Therefore, the purpose of this study was to characterize the behavior of selected fuel system elastomers in petroleum fuels and contrast this with the behavior in example alternative fuels. From this comparison the overall compatibility of these alternative fuels with the selected fuel system elastomers was assessed. The volume swell behavior of four nitrile rubber, two fluorosilicone and two fluorocarbon elastomeric O-ring materials as well as four sealant
elastomeric materials was measured in nineteen conventional JP-5 and JP-8 jet fuels, fourteen conventional F-76 diesel fuels, three alternative jet fuels, and three alternative diesel fuels. The volume swell of the materials in the conventional fuels was used to characterize normal volume swell behavior; then the volume swell in the alternative fuels and the predicted volume swell in 50-50 blends of alternative and conventional fuel were compared to normal volume swell behavior.
Overall, the volume swell behavior of the nitrile rubber materials in the alternative fuels and the predicted 50-50 blends deviated the most from normal volume swell behavior, followed by the sealant materials, then the fluorosilicone materials, and finally the fluorocarbon materials. The nitrile rubber materials exhibited significantly lower volume swell in the alternative fuels and the predicted 50-50 blends than in the conventional fuels. The sealant materials also showed generally lower volume swell in the alternative fuels and predicted 50-50 blends, with some of the material and fuel combinations reaching normal volume swell behavior. Finally, the fluorosilicone and fluorocarbon materials largely exhibited normal volume swell behavior in the alternative fuels and predicted 50-50 blends. Therefore, the nitrile rubber and sealant materials showed the greatest potential for having compatibility issues with the tested alternative fuels, while the fluorosilicone and fluorocarbon materials appeared to be compatible with the tested alternative fuels.