An experimental study of the behavior of liquid jets subjected to thermodynamic subcritical and supercritical conditions

As pressures and temperatures have risen in internal combustion engines, liquid fuel injection into an environment exceeding the critical pressure and temperature of the fuel is routine. If the fuel/oxidizer mixture reaches critical conditions, surface tension vanishes while the vapor/liquid density ratio approaches unity, altering the mixing behavior of the fuel and oxidizer from the well-studied behavior of jets injected into environments of more modest pressures and temperatures.; To elucidate these issues, an experimental study of n-pentane jet breakup in high pressure and high temperature nitrogen environments was performed. Specifically, n-pentane at 20°C was injected transversely into nitrogen through a plain orifice atomizer at velocities varying from 1.0 m/sec to 6.0 m/sec. The nitrogen temperature and pressure were varied from 20°C to 300°C and 100 psig to 1500 psig, respectively. The experiments were carried out in an optically accessible test chamber and two-dimensional spontaneous Raman imaging was employed to attempt to quantify the degree of jet vaporization.; An analysis of the jets' breakup mechanism, continuous length, drag coefficient and wake fuel concentration was conducted to determine if jet behavior at extreme pressures and temperatures could be explained by the characteristic decrease in surface tension and increase in gas/liquid density ratio as the critical point is reached. Though not all results could be explained by the appropriate changes in surface tension and the gas/liquid density ratio, jet behavior at ambient conditions in excess of the liquid critical point was observed to differ from behavior typical of jets injected at relatively low pressures. Furthermore, little variation in wake intensity was seen, but this is conceivable considering the inherent difficulties in spontaneous Raman scattering, most notably, its intrinsic weakness. Suggestions for improving the results of the Raman measurements employed in this investigation as well as possible modifications to the technique are discussed with the aim of rendering future Raman investigations of multiphase flows viable.