Three-dimensional imaging of swirled spray injection in a generic aero engine burner under realistic operating conditions

Joachim Klinner,Christian E Willert

doi:10.1007/s00348-021-03343-z

Abstract

Tomographic shadowgraph imaging is applied to reconstruct the instantaneous three-dimensional spray field immediately downstream of a generic aero engine fuel injector. Within the swirl passage of the injector model, a single kerosene jet undergoes air-blast atomization in a cross-flow configuration at Weber numbers of text {We}=360-770, air pressures of p_a=4-7,text{ bar } and air temperatures of T_a=440-570,text{ K }. High-speed, high magnification shadowgraphy is used to visualize the initial fuel atomization stages within the fuel injector before the spray enters the spray chamber. The 4-camera tomographic measurement setup is described in detail and includes a depth-of-field analysis with respect to droplet size based on Mie simulations and calibration data of the point-spread function. For a volume size of 16times 13times 10,text{ mm}^3 , the smallest resolvable droplet diameter is estimated to be d=10,mu text{ m } within the focal plane and increases to d approx 20,mu text{ m } toward the edges of the volume. Droplet velocities above the resolution limit were retrieved by 3-d cross-correlation of two volumetric reconstructions recorded at two consecutive time-steps. This is accompanied by an error analysis on the random error dependency on the camera viewing geometry. The results indicate increasing motion and fluctuations of the spray tail with increasing temperature and Weber number. Validation against PDA data further downstream of the burner plate revealed consistency for size classes d=10,mu text{ m } and d=15,mu text{ m }. Deviations from PDA occur in regions with strong velocity gradients due to different spatial resolutions, the presence of reconstruction ambiguities (ghost particles), uncertainties inherent to the two-frame cross-correlation of spray volumes and the finite LED pulse duration.Graphical

Highlights

The optimization of aero engine combustors requires a detailed knowledge of the fuel atomization process including fuel placement, breakup length scales, spray penetration depth, droplet sizes and velocities
At the lowest Weber number, column break-up can be observed as indicated within the circled regions which move at convection velocities of approximately 30 m/s
Variations of the position where the liquid column fractures can be observed in the animations provided in the supplemental material

Summary

Introduction

The optimization of aero engine combustors requires a detailed knowledge of the fuel atomization process including fuel placement, breakup length scales, spray penetration depth, droplet sizes and velocities. The acquisition of relevant experimental data on kerosene atomization on the other hand raises significant challenges such as providing realistic operating conditions and sufficient optical access. Another obstacle is that the dispersion of liquid kerosene by aero engine fuel injectors is driven by a highly threedimensional, typically swirling flow. Air-blast atomization of liquid kerosene films or jets is applied. The jet or film breakup in itself already is a highly complex process and subject of a large body of literature. Aside from the visualization of the initial spray column at its point of injection, the instantaneous three-dimensional placement of atomized fuel within the combustion volume is mapped both spatially and temporally

Methods

Results

Discussion

Conclusion