Measurements of Jet A Vapor Concentration Using Interband Cascade Laser

Abstract

The nonintrusive laser-based sensor is developed to measure the concentration of vapor-phase Jet A in the pulse detonation engines (PDEs). The sensor utilizes a distributed feedback (DFB) interband cascade laser (ICL), whose centered wavelength is at 3.411 μm. The concentration of vapor-phase Jet A is determined via tunable diode-laser absorption spectroscopy (TDLAS) technique using Beer’s absorption law. Calibration measurements have been carried out in a static cell to determine the line strength of vapor-phase Jet A-1, and the results have been applied to the concentration measurements. The sensor has been used to determine the time-resolved fuel concentration during the fuel injection as well as the arrival time of fuel to the head end of the PDE tube. The stoichiometry data shows fuel distribution is not uniform along the PDE tube wherein there exists a rising portion, a constant fuel concentration portion, and a descending portion. At the cases of nearly stoichiometry and fuel rich, the measured fuel concentrations are close to assumed concentration; however, at the case of fuel lean, there is an overestimation in the measured fuel concentration. The reasons could be attributed to fuel aerosols. The laser light can be also attenuated by droplet scattering when fuel aerosols are present in the laser beam. Nevertheless, there is a discrepancy between the measured fuel concentration and assumed concentration; the stoichiometry data still provide the information about the fuel distribution in the PDE tube and also give a better understanding of heterogeneous jet-fuel/air mixture sensing techniques.