Studies of Injection of Jet Fuel at Supercritical Conditions

At temperatures above 400 °C and at fuel system pressures, JP-8 and Jet A jet fuels exist as supercritical fluids. Fuel nozzles operating under conventional aircraft (subcritical) conditions atomize liquid fuel streams into droplets. The physical injection and mixing mechanisms associated with a nozzle operating under supercritical conditions are very different from those occurring under subcritical conditions. The current research examines the flow of fuel at supercritical conditions through a simple nozzle into a region that is also at supercritical conditions. Schlieren images of supercritical jet fuel exiting a simple nozzle into an optical chamber are presented. Computational fluid dynamics simulations of the flow were performed using n-decane as a surrogate fuel because it has a critical temperature and pressure similar to the pseudo critical temperature and pressure of the jet fuel sample used in the experiments. The results of the computational fluid dynamics simulations and the measurements obtained from the recorded images show that n-decane is a reasonable surrogate for Jet A fuel for predictions of the spreading angle and jet penetration length. Measurements and computation show that jet penetration and spreading angle are dependent on the fuel exit temperature and mass flow rate. In addition, it was found that the penetration depth of a supercritical jet into the optical chamber is less than that for a subcritical jet with the same fuel mass flow rate and pressure conditions.