LAUSR

Abstract Lubricity improver additives are adsorbed on sliding surfaces and form boundary films. Although for most additives, the films are monolayers, multilayer adsorption does occur in tribological contacts. However, to date, the isotherms adopted to study the adsorption thermodynamics for tribological systems are limited to monolayer films. To address this, the original Brunauer–Emmett–Teller (BET) gas adsorption isotherm was modified for use in dilute liquid solutions. The modified BET isotherm was used to fit experimental wear data collected using high frequency reciprocating rig (HFRR) for ultra-low sulphur diesel (ULSD) fuels containing trace levels of commercial lubricity improving additives. The results suggested that for certain additives in ULSD, the boundary film is multilayer.