Wilson line determination for 2-2-4 trimethyl-pentane (iso-octane)

Traditionally, properties for most substances are determined using graphs or equations obtained under thermodynamic equilibrium, however, real processes seldom occur in such circumstances. In a system under non-equilibrium thermodynamic conditions, condensation does not begin precisely when saturation is reached, this delay in the onset of condensation is called supersaturation and is defined as the ratio of the instantaneous fuel partial pressure to its vapour pressure. The onset of homogeneous nucleation (start of condensation), in terms of thermodynamic properties, is commonly called the Wilson point. The Wilson line is defined by a series of Wilson points obtained at different expansion conditions and represents the deviation with respect to the equilibrium condition in the process of condensation. This line was determined for iso-octane in the present work, at low expansion rates, based on a significant amount of measurements of pressure, temperature and drop size during expansion processes out of equilibrium in a combustion vessel at laminar and turbulent conditions.