oa Investigation into the impact of gas-to-liquid fuel components on elastomeric sealing materials in a gas turbine engine

Background & Objectives With the aim to become the Gas-to-Liquid (GTL) capital of the world, Qatar has put great effort into the research of adopting GTL fuel to replace conventional petroleum-derived fuel in current aircraft engines. One of the crucial aspects is the elastomer compatibility issue, as it is believed that GTL fuel may cause seals to shrink or no longer provide an effective sealing due to the lack of aromatics. The purpose of this project, funded by Qatar Science and Technology Park (QSTP), is to investigate the effects of GTL fuel components on O-rings made from various materials. Methods Stress relaxation test is employed for the purpose using the Elastocon Relaxation Tester. Three O-ring materials were tested, namely nitrile, fluorosilicone, and fluorocarbon. N-decane and ShellSol T solvent were chosen to represent normal and iso-paraffins respectively, as they are the main components of GTL fuel. Decalin, a cycloparaffin is included to form a triangle with the other two as previous research indicated cycloparaffin may have the potential to promote seal swelling. 25 blends were prepared with various proportions of the three solvents. Results The results indicated that both fluorosilicone and fluorocarbon O-rings showed excellent compatibility with all 25 blends tested. The stress relaxation characteristic of nitrile O-ring was highly dependent on the composition of the solvents; the more decalin (n-decane) is in the blend, the better (worse) its sealing performance becomes. Effects of the three solvents presented in the tests indicated aromatics are not the only compounds that can swell nitrile O-ring. N-decane also showed certain O-ring swelling ability but its main effect during the polymer-fuel interaction process is to extract materials out of nitrile O-ring. Iso-paraffins do not participate in the O-ring swelling process but only extract polymer materials; however its extraction ability is relatively weaker than n-decane. Conclusions Fluorosilicone and fluorocarbon O-rings are fully compatible with GTL fuel, while nitrile material may shrink when exposed to it. Decalin is capable to swell nitrile O-ring; however, the proportion of decalin in the solvent has to be no less than 60% to be comparable to Jet A-1.