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

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 similar to 300 to 530 K and pressures to similar to 160 MPa for three different types of diesel fuels in N-2 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 similar to 165 MPa for mixtures with N-2 content ranging from similar to 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 + N-2 mixture data provide a rational basis for determining values for k(ij), a binary mixture parameter needed for EoS calculations. Modeling results show that the temperatures predicted for diesel + N-2, 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.