ABSTRACT The use of hydrogen as a sustainable energy carrier poses significant challenges for lubrication in technical systems, such as combustion engines and compressors. In addition to the low viscosity of hydrogen, water formed during combustion can dissolve in lubricating oils and alter their physical properties. In this study, the density of an American Petroleum Institute (API) Group V base polyalkylene glycol (PAG) oil was investigated as a function of temperature and pressure at two different water contents. Density measurements were carried out using a vibrating‐tube densimeter in a temperature range from 265 to 465 K and at pressures between 1 and 1400 bar. The results show a negative molar excess volume at low temperatures, which increases with temperature and approaches zero at approximately 430 K. At temperatures above 430 K, the molar excess volume becomes positive. The high‐water solubility of PAG oils and the associated changes in density indicate that their application in hydrogen‐related systems requires particular caution.
Richter et al. (Sun,) studied this question.