Numerical Simulation of Injection of Supercritical Ethylene/Methane into Nitrogen

Abstract

The present study investigates the physical mechanisms of supercritical fluid injection for pure ethylene and ethylene/methane mixtures, as well as onset of condensation upon fluid expansion. These mechanisms are considered a key enabling technology in the design of hydrocarbon-fueled scramjet engines. The numerical method combines a solution of the compressible Navier-Stokes equations for the supercritical fluid with two different approaches for condensate growth: one based on a homogeneous equilibrium assumption and the other on classical aerosol dynamics. The thermodynamic behavior of the supercritical fluid is described using the Peng-Robinson equation of state. Computational results are compared with shadowgraph and direct-lighting imaging data, mass flow measurements, mole fraction measurements and temperature measurements in the jet mixing zone, and pressure distributions within a three-dimensional injector geometry. Qualitative results involving jet structure, the appearance of a condensed phase, and the general effects of back pressure and injectant temperature are in good agreement with experimental results for pure ethylene injection. Quantitative results also display reasonable agreement with experimental results but do indicate the need for improving the model. Qualitative trends for ethylene/methane mixture injection are in moderate agreement with the experimental data, suggesting that the thermodynamic interaction between ethylene and methane as modeled by the chosen mixing rules are not sufficiently accurate.

For conditions where both are applicable, a finite-rate (nucleation/growth) phase-transition model presents essentially the same bulk fluid response as a homogeneous equilibrium model with additional predictions of number density and average droplet size.