Unlubricated engines can be realized from the tribological point of vi
ew if volumetric wear coefficients of sliding couples lower than 5.10(
-8) mm3/(N.m) can be demonstrated. A review of published tribological
data and a search of a large database provided no couples with such lo
w wear coefficients at 22-degrees-C and 400-degrees-C. However, known
sliding couples with volumetric wear coefficients near 10(-7) mm3/(N.m
) make it practical to build up such engines for basic studies. Synerg
istic material dry lubrication concepts may further reduce wear.