Investigating the interaction of an annular air jet with a spray flame using phase-Doppler interferometry and laser-induced fluorescence

Abstract

This thesis describes an experimental investigation of the interaction of an annular air jet with a spray flame using phase Doppler interferometry (PDI) and planar laser-induced fluorescence (PLIF). The geometry studied consisted of a standard 75-60* A pressure-swirl nozzle concentrically located in a 63.6mm x 50.4mm annular air jet. Methanol fuel was sprayed from the nozzle at a flow rate of 0.42 g/s and ignited. Measurements were made in the resulting spray flame, with annular air flow rates of 0, 2.38, 4.77, 7.15 and 9.52 l/s (Reynolds numbers based on bluff body diameter of 0, 6500, 13000, 19500 and 26000 respectively). Photographic images were made using laser sheet lighting to illuminate a centreline slice of the spray, and instantaneous and time-averaged planar laser-induced fluorescence images of OH fluorescence were made, showing reaction zone locations. Quantitative OH concentrations were extracted from the PLIF images. An attempt to obtain PLIF images of CH fluorescence in the spray flame was unsuccessful. Phase Doppler interferometry measurements allowed mapping of fuel droplet size and velocity distribution, as well as local volume flux. Post-processing of PDI data allowed determination of the gas-phase velocity. A method was developed to enhance the visibility of seed particles in the presence of large droplets and thus increase data rates, and was applied to the spray centreline to obtain turbulence information including local integral timescales and turbulent energy spectra. Temperature measurements were made using thermocouples in regions where droplet impingement was not significant. It was found that the annular air jet profoundly influences the spray flame, reducing the overall flame height by half, and changing the structure from a two reaction zone system to a single reaction zone system. The annular air jet tended to direct droplets toward centreline, thus providing a confinement effect.