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

TL;DR

This paper introduces a numerical framework using OpenFOAM to study real-gas effects and phase separation in underexpanded jets at engine-relevant conditions, revealing significant impacts on jet penetration and flow behavior.

Contribution

It presents a new open-source simulation framework combining a hybrid solver with a vapor-liquid equilibrium model for accurate underexpanded jet analysis.

Findings

Fuel type significantly influences phase separation occurrence.

Phase separation causes different jet penetration depths compared to single-phase models.

Expansion and mixing induce single-phase instability leading to phase separation.

Abstract

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