Real-Gas Effects and Phase Separation in Underexpanded Jets at Engine-Relevant Conditions

Abstract

A numerical framework implemented in the open-source tool OpenFOAM is\npresented in this work combining a hybrid, pressure-based solver with a\nvapor-liquid equilibrium model based on the cubic equation of state. This\nframework is used in the present work to investigate underexpanded jets at\nengine-relevant conditions where real-gas effects and mixture induced phase\nseparation are probable to occur. A thorough validation and discussion of the\napplied vapor-liquid equilibrium model is conducted by means of general\nthermodynamic relations and measurement data available in the literature.\nEngine-relevant simulation cases for two different fuels were defined. Analyses\nof the flow field show that the used fuel has a first order effect on the\noccurrence of phase separation. In the case of phase separation two different\neffects could be revealed causing the single-phase instability, namely the\nstrong expansion and the mixing of the fuel with the chamber gas. A comparison\nof single-phase and two-phase jets disclosed that the phase separation leads to\na completely different penetration depth in contrast to single-phase injection\nand therefore commonly used analytical approaches fail to predict the\npenetration depth.\n