A numerical study on jet characteristics under different supercritical conditions for engine applications

Fuel injection is one of the key factors that influence the energy conversion efficiency and emission level of engines. In this study, supercritical injection and mixing under different conditions were investigated using large eddy simulation method. Real-fluid thermodynamic models based on the Peng-Robinson equation of state, including the volume-translation method, were established, and the adjusted pressure implicit split operator algorithm was developed to handle solution instability due to thermodynamic nonidealities. Density variations, potential core lengths, spreading rate, and turbulent velocity fluctuations were analyzed. The effects of injection temperature and ambient pressure on supercritical jet disintegration were studied. The results show that both high injection temperature and elevated ambient pressure can facilitate jet mixing, and the potential core length and spreading rate are sensitive to the injection temperature near pseudo-boiling point. The pseudo-boiling process, which results in a large density gradient and isobaric heat capacity in the jet surface, delays the shrinkage of the radial boundary of the potential core and leads to small spreading angles of jets. The turbulent velocity fluctuations reveal significant anisotropy in the mixing layer of supercritical jets, and a large density gradient resulting from pseudo-boiling behavior damps radial turbulent velocity fluctuations at the surface of jets.