On the influence of geometrical parameters on the spray characteristics of high shear injectors

Abstract

We discuss the influence of geometrical parameters over the performance of high shear injector. High shear injector usually consists of a series of air swirlers (primary and secondary) with diverging flare at the exit and centrally mounted fuel nozzle. In this study, we have considered only parameters pertaining to air swirler i.e. geometrical swirl number (SNgeo), flow split ratio (γ), area ratio (Δ), flare angle (θ) and flow orientation of primary and secondary swirlers (co/counter rotation). The above parameters were categorized into two paradigms, first, SNgeo, γ, Δ are designated as internal geometrical parameters, which induces variations in the bulk Reynolds number at the exit. On the other hand, parameters like flare angle (θ), flow orientation doesn’t yield any variations in bulk Reynolds number. Time resolved PIV (Particle Image Velocimetry; ~ 3500 frames/s) is employed to extract the topological structures of the flow field. The length scale (W/Df), which embodies the radial extent of the recirculation zone is governed by near field swirl number (SN10) and Reynolds number for cases with variations in SNgeo, γ, Δ. Contrarily, with variations in θ and flow orientation, (W/Df) is found to be a function of near field swirl number f (SN10) only. The spatial distribution of the spray shows linear relationship with the W/Df. Finally, the droplet size spectrum obtained from 3D PDI (Phase Doppler interferometer) also shows insensitivity with respect to the different test cases. This clearly indicates that in high shear atomizer configuration, spread of the spray can be altered without deterioration in uniformity and droplet size distribution.