Flow and Temperature-field Structure of Turbulent Spray Flames: From Dilute to Dense

Abstract

The novel diagnostic approaches employed in this dissertation showcase the on-going development of experimental datasets in turbulent spray jets and flames; for both physical insight and model validation. The piloted Sydney Needle Spray Burner (SYNSBURNTM) is introduced for this purpose, featuring air-blast atomization with liquid injection from a needle that can be translated within a co-flowing air stream. The pilot-stabilized spray flames can range between the two extremes of dilute and dense by physically translating the needle tip relative to the burner’s exit plane. The burner provides a versatile platform for studying complex multi-phase flows more akin to practical combustors and the resulting analysis has proved useful in the development and validation of related models for turbulent spray jets and flames. The stability characteristics for these spray flames are presented for multiple recess lengths using acetone, ethanol and biodiesel fuels. LDV/PDA and high-speed shadowgraphy are performed in the dense atomization region of spray jets and flames to characterise the flow-field. A novel classification scheme based on shape is developed and used to clearly define the boundary conditions and to map the evolution of liquid fragments. The characteristic final breakup point of the liquid column, as well as the onset of primary and secondary atomization regimes are spatially-resolved using these techniques. The first temperature measurements in turbulent dilute and dense spray flames using single- laser-shot chirped-probe-pulse femtosecond coherent anti-Stokes Raman spectroscopy (CPP-fs-CARS) are demonstrated and the subsequent dataset analysed. The state-of-the-art 5 kHz CPP-fs-CARS system has achieved integration times of 3 picoseconds (ps) as well as spatial resolution of approximately 800μm along beam propagation and 60μm in the transverse dimension. New details of the technique, calibration, correction of interferences, and spectral fitting procedures relevant to turbulent spray flame thermometry are presented, along with estimates of the associated error. The measurements are validated against well-established datasets in comparable gaseous flames. The thermal structure of spray flames is spatially and temporally resolved. The correlation between the flow and temperature-field show that thermal structures in turbulent spray flames are affected by liquid morphology in the near-field. The wealth of information available in these combined datasets has provided great insight into partially-premixed combustion.