Elastomer Compatibility Test of Alternative Fuels Using Stress-Relaxation Test and FTIR Spectroscopy

Abstract

Global efforts to reduce CO2 emissions and to tackle the problem of depleting petroleum resources have stimulated the exploitation of alternative fuels in the aviation industry. One crucial aspect amongst others is to investigate the compatibility of alternative fuels with elastomeric materials currently used in gas turbine engines. However, little knowledge about this has been understood so far for commercial aircrafts under real engine conditions. This study combines Stress-Relaxation test and FTIR spectroscopy techniques to look at the effect of alternative fuels on O-rings made from different materials; such as nitrile, fluorocarbon and fluorosilicone. Results indicated that after immerged in fuels for a period of time while simultaneously being compressed at certain temperatures, the fluorocarbon O-rings showed minimum change in the eight types of fuels tested. This meant they are compatible with these fuels, with the nitrile O-rings changing the most. Furthermore, FT-SPK+20% hexanol caused the biggest relaxation in fluorosilicone O-rings but had the smallest effect on nitrile ones while all fuels presented similar behavior in fluorocarbon. FTIR spectrum analysis showed molecular composition changes are dependent on the reactions between different materials and fuels. For fluorosilicone O-rings, the absorbance reduction from 1150 to 1050 cm−1 was caused by the breakdown of (Si-O-Si) while the formation of new O-H bonds enhanced the intensity from 3000 to 2800 cm−1. For fluorocarbon O-rings, obvious increase in absorption could be found in the region from 1400 to 650 cm−1, while from 3000 to 2800 cm−1, the absorption decreased. Multiple linear regression analysis indicated a highly correlated relationship between the chemical structure changes and the force relaxation.

Investigation into the Impact of n-Decane, Decalin, and Isoparaffinic Solvent on Elastomeric Sealing Materials

“…Counterforce decreased sharply with time during this phase as elastomeric material is viscoelastic, which means it has both the properties of viscous and elastic materials and, as such, exhibits time-dependant strain [10]. Time periods of this phase for decalin and n-decane lasted for 3 hours since compressions were applied.…”

“…When normalized by the stress relaxation characteristics in Jet A-1 fuel with comparison to GtL [11] (Figure 3(b)), it can be seen that nitrile O-ring in decalin showed even better relaxation performance than that in Jet A-1. O-ring swelled to a larger amount of volume and relaxed slower afterwards, which suggests that pure decalin has good nitrile O-ring swelling property.…”

Measurements of Nitrile Rubber Absorption of Hydrocarbons: Trends for Sustainable Aviation Fuel Compatibility

“…N-/iso-alkanes were not evaluated as dopant molecules here because they are known to have an insignificant influence on o-ring swell. 9,10,29,30 Eleven different shipments of petroleum-based jet fuel used in an extensive report on this topic 9 along with three additional samples of petroleum fuels from the National Jet Fuels Combustion Program (NJFCP) 31 were used to set a three-standard deviation experience range for the o-ring swelling activity of conventional jet fuel. The aromatics fraction of these fuels varies between 11.9 and 23.1%v.…”

Future-Oriented Experimental Characterization of 3D Printed and Conventional Elastomers Based on Their Swelling Behavior

“…On a bigger scale, fuel-burning tests [40] or ultimately flight tests are conducted. Regarding material compatibility, mechanical studies are essential to investigate the tightness of seals [41], leakage due to shrinkage, when refueling or mechanical properties in dependence of the swelling status [42]. Whereas previous work is often limited to the interactions of pristine elastomer with fuels or fuel-like substances, the current study aims to estimate long-term effects by conducting experiments with pre-aged elastomers.…”