Large eddy simulation and proper orthogonal decomposition analysis of fuel injection under trans/supercritical conditions

Abstract

Heptane jets with subcritical and supercritical inlet temperatures injected into a supercritical environment filled with multi-component gas have been numerically investigated using large eddy simulation. Main attentions are paid on the effects of density-gradient, thermodynamic and transport properties on the jet flow evolution. It is found that large density-gradients are easier formed in transcritical injection and the larger specific heat has an effect of forming the density gradients, while the diffusion coefficients decrease in the larger density gradient regions, suggesting that large density gradient has the effects of suppressing the flow diffusion mixing. In addition, when the fluid transits across the pseudo boiling temperature, the specific heat reaches a maximum value, yet this value is suppressed by the dissolution effects, indicating that multi-component injection is different from the single species injection and a special investigation is needed. The disintegration features in transcritical and supercritical injections are different, and thermodynamic and transport properties are crucial in the disintegration process. A proper orthogonal decomposition analysis indicates that the turbulent kinetic energy is larger and vortexes are more easily formed in the supercritical injection. The vortex movement and paring significantly affect in the jet mixing process.