Effect of n-Alcohol addition to jet fuel (JP-5) on the swelling and tensile strength of additively-manufactured (AM) methacrylate and commercially-manufactured Buna-N O-rings

• Alcohols (methanol to octanol) swell AM O-rings more than JP-5 does. • Buna-N O-ring swelling: JP-5> larger alcohols >smaller alcohols. • Some alcohol mixtures produce higher swells than JP-5 or alcohol alone. • Pressure testing reveals O-ring durability problems. • Tensile strengths decrease as swelling increases. The addition of alcohols to fuels is one approach to reducing the amount of carbon in fuel sources, and thus the impact of alcohols on engine components needs to be evaluated. This work investigated the effect of adding alcohols to jet fuel (JP-5) on the swelling and tensile strength of commercially produced Buna-N O-rings and additively manufactured (AM) acrylate O-rings. O-rings were exposed to JP-5, pure alcohols (methanol to n -octanol), and alcohol mixtures up to 30 % for seven days. The volume percentage swells ranged from −1 to 58 %. The AM O-rings swelled more in the pure alcohols (>46 %) than in JP-5 (17 %), while the Buna-N O-rings swelled more in the JP-5 (25 %) than in the alcohols (< 9 %). For Buna-N, the volume change of the larger alcohols was greater (∼8 %) than those of the smaller alcohols (<5 %), while no specific trend was seen for the AM O-rings. For the Buna-N O-rings all of the blends of alcohol and JP-5 produced larger volume increases than those induced by the alcohol or JP-5 alone. This also occurred for the higher concentrations of alcohol blends with the AM O-rings. The swelling reduced the tensile strength of the O-rings by as much as 60 % for the Buna-N O-rings and 88 % for the AM O-rings. Evaporation of the alcohols from the O-rings for three weeks or more caused the Buna-N O-rings to shrink by up to 11 % and for the tensile strength to increase by around 26 %. The shrinkage was less for the AM O-ring (∼3 %), but the increases in tensile strength ranged from 10 to 50 %. The synergistic behaviour of alcohols and fuels to enhance O-ring swelling found in this study encourages those selecting O-rings for a particular application to conduct testing on the actual fuel blends.