Near-frictionless carbon coatings for spark-ignited direct-injected fuel systems. Final report, January 2002.

Abstract

EXECUTIVE SUMMARYThis report describes an investigation by the Tribology Section of Argonne National Laboratory (ANL) into the use of near-frictionless carbon (NFC) coatings for spark-ignited, direct-injected (SIDI) engine fuel systems. Direct injection is being pursued in order to improve fuel efficiency and enhance control over, and flexibility of, spark-ignited engines. SIDI technology is being investigated by the Partnership for a New Generation of Vehicles (PNGV) as one route towards meeting both efficiency goals and more stringent emissions standards. Argonne's approach to these friction and wear issues was to investigate the applicability of NFC to fuel system parts. In collaboration with Delphi Automotive Systems and BP Amoco plc, Argonne carried out two tasks: optimize the deposition of NFC onto standard flats and balls as well as production fuel injectors, and perform both industry-standard lubricity tests and customized wear tests designed to simulate the engine environment. These tests were performed with several gasolines and other fuels, and the NFC performance was compared to that of uncoated parts and other commercially available coatings, all applied to production fuel injectors. Finally, to understand the wear mechanisms, Argonne applied advanced characterization techniques to the worn and unworn coatings, the steel against which they wore, and the wear debris. The industry-standard lubricity tests included the Falex ball-on-three-disc (BOTD) test, while the customized wear testing was performed in a sealed reciprocating system designed to perform fretting wear tests. Long-duration reciprocating tests were performed with a ii total sliding distance of 2 km in order to determine the steady-state performance of the NFC coatings. The worn surfaces were examined by 3D optical profilometry to determine wear rates.The advanced characterization methods applied included Raman spectroscopy and laser scanning measurement of residual stresses in the NFC coatings.In the customized reciprocating tests, comparisons between two varieties of NFC and three commercially available diamondlike carbon (DLC) coatings showed that the NFCs gave consistently high performance and were generally the best choice for reducing friction and wear, although one of the commercial DLCs achieved performance comparable to the NFCs in several individual tests. The other commercial DLCs displayed poor performance under certain conditions. In dry or ethanol-lubricated wear, NFC6 performed the best; when subjected to E85 or M85 fuel, the commercial DLC gave the best results; and NFC2 displayed the lowest friction and wear rate of the three in regular gasoline, the most relevant condition for fuel injector applications. NFC2 reduced friction in all the liquids tested, compared to tests of uncoated materials in the same fluids; NFC6 did also but not to as great an extent.The long-duration tests designed to determine the ultimate wear lifetime of the NFC coatings on injectors in current-and next-generation gasolines showed that NFC6 pro...

Small amplitude reciprocating wear performance of diamond-like carbon films: dependence of film composition and counterface material

“…The 57 sp 3 /sp 2 ratio, which strongly influences film properties, 58 depends on the hydrogen content of the film and the 59 deposition parameters, such as pressure, ion impinge-60 ment energy, and the surface power density at the sub-61 strate [12,13]. 62 The tribological characteristics of DLC films have 63 been the subject of a large number of investigations 64 because of the high hardness and low friction that these 65 films generally possess [14][15][16][17][18]. A wide range of results 66 has been reported because of differences in methods of 67 synthesis, film structure, and thickness, and test envi-68 ronment and procedures.…”