Diffusion coefficients of diesel fuel and surrogate compounds in supercritical carbon dioxide

Facilitating a new concept of clean diesel combustion using supercritical fluids requires a better understanding of thermophysical properties of the diesel fuel/diluent system. Mass diffusivity is one such property that is important to understand diesel fuel/diluent mixing and spray and combustion of supercritical fuel mixtures. In this work, diffusion coefficients of diesel fuel and surrogate compounds in supercritical carbon dioxide were experimentally determined by the Taylor dispersion method at temperatures from 313.15 to 373.15 K and pressures up to 30 MPa. Difficulties were encountered to measure diffusion coefficients using the Taylor dispersion method near the critical region of CO₂ which resulted in curve-fitting errors greater than 5%. Predictive correlations including Wilke-Chang, Scheibel, and He-Yu were examined. Diffusivity data were also fitted by D₁₂/T - η and D₁₂ / sqrt(T) - ρ correlations. Results showed that the He-Yu correlation has the best prediction performance while the D₁₂/T - η correlation best fits the data with AAD% < 8%.