Spray Characterization of a Preheated Bio-Oil Surrogate at Elevated Pressures

Abstract Atomization plays an important role in the gasification or combustion of bio-oils, where the atomizer parameters need to be properly controlled to efficiently atomize a highly viscous liquid at elevated pressures with imparting the least amount of kinetic energy to the discharged droplets because of evaporation and chemical reaction constraints. With a focus on bio-oil deployments in micro gas turbines, an aqueous surrogate of a preheated bio-oil injected from a twin-fluid atomizer is used in the present study for spray size and velocity measurements at elevated pressures. The experiments were conducted in High Pressure Spray Facility of the National Research Council of Canada (NRC) using various optical diagnostics including laser sheet imaging (LSI),phase Doppler anemometry (PDA), and laser diffraction (LD). A scaling strategy was adopted to conserve the ranges of gas-to-liquid momentum flux ratio, M, at different working pressures, P. The spray cone angles are found to be insensitive to P, but they decrease with increasing M. For a constant value of M, droplet mean diameters increase and their corresponding velocities decrease with increasing P, attributed to the effect of gas-to-liquid density ratio on the primary breakup of a liquid jet in a coaxial gas stream. To predict the Sauter mean diameter of spray droplets, a correlation previously reported in the literature is modified and a novel correlation is proposed based on four dimensionless groups, namely gas Weber number and gas-to-liquid momentum flux ratio, density ratio, and viscosity ratio.