Srikrishna Sahu

The current research work focuses on spray characterization in a model Lean Premixed and Pre-vaporized (LPP) atomizer that aims to minimize NOx emission in gas turbine combustors. The injector allows cross-stream atomization of two radially injected liquid jets from a central hub due to the crossflowing air within a surrounding annular region. Both non-swirling and swirling air flows were considered. Optical measurement of spray characteristics is reported for a range of aerodynamic Weber number, (Weg ≈ 40–140) and momentum flux ratio, (MFR ≈ 3–7) that ensured that the jet–wall interactions leading to liquid films were avoided prior to completion of the jet breakup. Planar laser sheet imaging of the spray illustrated significantly wider dispersion of the spray droplets and modification in the overall spray structure due to introduction of air swirl upstream of the liquid jets within the atomizer. The droplet size and all three velocity components were measured using a Phase Doppler Particle Analyzer (PDPA) technique. The SMD was found to significantly reduce with increase in Weg for swirling as well as non-swirling crossflows. The tangential and radial velocity of droplets increased under the presence of swirling air as compared to non-swirling crossflow. The proper orthogonal decomposition (POD) analysis of the spray images was done which revealed the dominant structures in spray. The second and third POD modes were found to depict the alternate feature of region with concentrated droplet number density. Spray fluctuations due to unsteady jet breakup become dominant feature over flapping of spray structure for higher Weg.

This paper investigates the influence of concentration of boron nano-particles on the combustion behavior of Jet A1-based slurry droplets especially for high-particle loadings. The nanofuel was prepared using commercially available boron nano-particles. The particle loading ratio (by weight) was varied from 2.5 to 50%. Shadowgraphic visualization of the burning droplet and direct flame imaging was carried out to examine the burning characteristics of horizontally suspended slurry droplet. While for particle loading up to 20%, the droplet combustion was dominated by vigorous oscillations and micro-explosions, beyond 20% loading, significant differences in the combustion behavior were observed which are discussed. The normalized surface area plot supported the observations and depicted clear departure from classical model for droplet burning.

In liquid-fueled combustion, the interaction of spray droplets with surrounding turbulent air flow is crucial since it influences the evaporation rate of the fuel droplets and the process of air and fuel vapor mixture preparation. For detail understanding on the droplet-turbulence interaction mechanisms as well as to validate numerical simulations of sprays, simultaneous measurement of both dispersed and carrier phases of the spray is essential. This way the vortical interaction of droplets can be fully characterized such that important issues such as local spray unsteadiness and spatiotemporal inhomogeneity of droplet concentration due to droplet clustering and group evaporation of droplets can be addressed. This review focuses on the advances in the optical diagnostics (especially the planar techniques) in the last few decades to meet these requirements. Due to broad size and velocity distributions of spray droplets, the application of the two-phase measurement techniques to sprays encounters challenges especially in phase discrimination. Additionally, for sprays, it is not sufficient to simultaneously measure two-phase velocities but the droplet size is also important since the dynamic drag on droplets is according to their size and velocity relative to the surrounding gas flow. The techniques with such capability are explored. The sources of uncertainty and advantages and limitations of different two-phase measurement approaches are analyzed according to their application to dense and dilute sprays.

This paper reports an experimental study of spray characteristics in rotary slinger atomizers using different laser diagnostic tools. The main objective of the present study is to investigate the effect of size of the slinger orifices on liquid breakup dynamics and droplet size distribution over a wide range of rotational speed (5000–45,000 rpm) and liquid flow rates (0.2–2 lpm). Three different slinger discs having the same number of orifices but different sizes (d0 = 1, 1.5, and 2 mm) are considered. The primary liquid breakup visualization is achieved using volumetric laser-induced fluorescence (VLIF) technique; whereas, the droplet size is measured by interferometric laser imaging for droplet sizing (ILIDS) technique. The results demonstrate critical role of orifice size on liquid breakup mode and droplet size up to rotational speed about 30,000 rpm, beyond which the aerodynamic force dominates the atomization process such that neither the orifice size nor rate of rotation has strong influence.