Analysis of transient evaporation characteristics of droplets and the driving mechanisms of thermophysical properties in supercritical environments

Droplets are fundamental components of fuel sprays, and the evaporation process significantly affects spray morphology and mixing efficiency. Current research has confirmed that droplet evaporation in supercritical environments deviates from the classical d ² law. This conclusion relies on complex evaporation mechanisms, yet the factors driving the transient characteristics of droplet evaporation under high pressure remain unclear. To address this gap, a finite-domain transient droplet evaporation model was developed to investigate the evaporation behavior of n-dodecane droplets under Engine Combustion Network (ECN) Spray A conditions. The model integrates variable thermophysical properties, adaptive meshing, and non-ideal gas effects to capture the coupled dynamics between heat and mass transfer. By constructing both baseline and modified thermophysical property models, the driving mechanisms of key thermophysical properties were systematically examined. The results reveal a significant deviation of the n-dodecane evaporation curve from the classical d ² law, dominated by transient evaporation with an increasing evaporation rate. Corrections to the saturated vapor/liquid density and isobaric heat capacity positively affect the transient evaporation rate. The influence of the former gradually weakens with increasing ambient pressure, while the latter is more sensitive to changes in ambient pressure, with its effect becoming significantly stronger at higher pressures. In contrast, Thermal conductivity corrections negatively affect the transient evaporation rate, an effect that diminishes as ambient pressure increases. Furthermore, the nonlinear deviation from the d ² law is attributed to strong coupling among thermophysical properties, rather than to any single non-ideal transient effect. These findings provide deeper insight into the droplet evaporation processes under high-pressure conditions, thereby improving the prediction of fuel spray dynamics and mixing efficiency.