Experimental and modeling investigations of the phase behavior and densities of diesel + nitrogen mixtures

Abstract

It has been recently speculated that diesel injection into a supercritical air environment at high-pressure, high-temperature (HPHT) conditions results in the diesel + air mixture transitioning into a single supercritical fluid phase. To help resolve this issue we report HPHT isothermal bubble (BP) point data from ~300 to 530 K and pressures to ~160 MPa for three different types of diesel fuels in N2 that is considered a surrogate for air. One of the diesels (Highly Paraffinic, HPF) has a larger paraffinic content relative to the others, another (Highly Aromatic, HAR) has a larger aromatic content relative to the others, and the third is a Ultra-Low Sulfur Diesel (ULSD) that resembles an unfinished commercial diesel. In addition, isothermal, density data are also reported at pressures from the BP to ~165 MPa for mixtures with N2 content ranging from ~3 to 55 wt%. The T, p range of the experimental data are extended with model calculations using the PC-SAFT equation of state (EoS) with pseudo-component parameters for diesel. Both types of diesel + N2 mixture data provide a rational basis for determining values for kij, a binary mixture parameter needed for EoS calculations. Modeling results show that the temperatures predicted for diesel + N2, supercritical fluid behavior can vary significantly depending on the method used to characterize the EoS properties of the complex diesel mixtures. Nevertheless, the predicted critical-mixture curves provide useful insight for interpreting the results from supercritical diesel spray investigations.