Droplet evaporation characteristics of hydrotreated vegetable oil (HVO) under high temperature and pressure conditions

To investigate hydrotreated vegetable oil (HVO) droplet evaporation characteristics under sub/trans/supercritical conditions, surrogate HVO droplet evaporation experiments were conducted under high temperatures (573–873 K) and pressures (0.1–2.0 MPa), and thermodynamic and physical properties were analyzed. The results reveal that HVO surrogate fuels have a lower density, surface tension, and boiling point, allowing better evaporation characteristics than diesel. HVO surrogate fuels exhibit shorter droplet lifetimes and higher evaporation rates than diesel under all ambient conditions. Among HVO surrogate fuels, HVO:C15-C18/isododecane has the shortest droplet lifetimes because adding iso-dodecane reduces the initial heating period due to a lower boiling point. It was found that the evaporation characteristics are affected by not only the boiling point but also fuel compositions and thermodynamic properties such as thermal conductivity, latent heat of vaporization, and specific heat of gas. Critical points (Tc, Pc) are important indicators for selecting evaporation conditions. Increasing temperature decreases droplet lifetime and increases the evaporation rate due to high heat transfer from the ambient gas. However, the effect of pressure on droplet lifetime relies on ambient temperature (Tamb). As pressure increases, droplet lifetime increases at Tamb < Tc and decreases at Tamb > Tc. Increasing pressure at Tamb ∼ Tc has no significant effect on droplet lifetime.