Spray characteristics of standard and alternative aviation fuels at high ambient pressure conditions

Abstract

The spray characteristics of standard and alternative aviation fuels generated by a hybrid pressure-swirl airblast (HPSA) atomizer were investigated at high ambient pressure conditions. The measurements were performed in an optically accessible pressure vessel at pressures of 1, 2, 3, 4, 5, and 9.5 bar with heated gas and fuel temperatures of 394 K and 332 K, respectively. The drop size and drop velocity of sprays from a standard (Jet-A) and an alternative (C-5) aviation fuels were measured using phase Doppler anemometry (PDA), and 2-D visualization of spray was imaged using simultaneous fuel-Planar Laser Induced Fluorescence (PLIF) and Mie scattering. The spatially resolved PDA drop size measurements were obtained at 25.4 mm downstream of the swirler exit plane and up to 30 mm in the radial direction from the spray centerline. The Sauter Mean Diameter (D32) was observed to decrease significantly with increasing ambient pressure, up to 5 bar. However, the change in D32 was observed to be limited with a further increase in the ambient pressure. A higher swirler pressure drop resulted in a significant reduction in the D32 at an ambient pressure of 5 bar. Using simultaneous fuel-PLIF and Mie scattering imaging, the feasibility of the laser sheet drop-sizing (LSD) technique was examined for the spray at high ambient pressure application. In addition, the effect of ambient pressure on the spray cone angle was investigated using both instantaneous and averaged Mie images. The distribution of fuel vapor and droplets in the spray was also imaged and identified by comparing instantaneous fuel-PLIF and Mie images. A phenomenological three-step atomization model was used to predict the drop size and demonstrate the drop size trend with increasing ambient pressure.