Friction and wear behavior of near-frictionless carbon coatings in formulated gasolines

Million-cycle reciprocating wear tests have been carried out to determine the ultimate wear lifetime of near-frictionless carbon (NFC) coatings applied to production fuel-injector tips. Wear tests were performed in existing and reformulated gasolines as part of a study to improve fuel systems for spark-ignited, direct-injected (SIDI) engines. Ball-on-three-disc (BOTD) tests were performed to determine the lubricity of the gasolines, and the wear surfaces were analyzed using Raman spectroscopy. NFC coatings reduced friction and total wear by up to 48% and 39%, respectively. No evidence was seen of coating graphitization, the formation of transfer films from the coatings, or the presence of chemical protective films originating from the gasolines.