A Tribochemical Analysis of Lubricants From Field Trials of Hydrogen-Assisted Dual Fuel Internal Combustion Engines

Abstract The article reports on the tribological performance of lubricant samples siphoned from hydrogen-assisted diesel engines of trucks participating in a real-world field trial. Lubricant rheology, as well as the ability of the residual additive package in forming tribofilms generated through tribometry is studied. Marginal changes in lubricant viscosity are noted with the use of hydrogen-assisted combustion due to the relatively short trial period. However, there are differences in lubricant chemistry and frictional behavior under boundary regime of lubrication ascertained using X-ray photoelectron spectroscopy. The tests show that friction increases as boundary interactions become dominant and higher coefficients of friction are consistently observed at lower applied loads under mixed and boundary lubrication conditions. The differences in tribological performance are more noticeable at higher contact pressures. The impact of hydrogen-assisted combustion on the performance of lubricants in formation of tribofilms under laboratory conditions is discussed. There are differences in frictional characteristics with the introduction of hydrogen even at the rather low hydrogen content in the dual-fuel intake. There are particular noticeable differences in mixed and boundary regimes of lubrication, owing to the variations in the surface topography and tribofilm compositions. The surface topography of samples and the presence of anti-wear additive constituents on the surfaces post-tribometric tests vary with the sliding speed. Gradual use of hydrogen as an assistive fuel in existing heavy-duty vehicle fleets offers a pragmatic transitioning pathway toward hydrogen-powered engines for haulage and off-highway applications.