Characteristics of gelled Jet A1 sprays formed by internal impingement of micro air jets

Abstract

This paper investigates the characteristics of highly viscous non-Newtonian gelled propellant sprays formed by internal impingement of micro air jets on the propellant stream. The newly developed atomizer is an improved alternative to the externally impinging jet designs, in that the high-momentum micro jets of atomizing air located internally and upstream of the atomizer exit orifice continuously impart high shear to the oncoming gelled propellant jet. Breakup and atomization is achieved within a short time and at a much smaller supply pressure of atomizing air than the other atomizers considered for this application. Spray characterization studies reveal that the Sauter mean droplet size of gelled Jet A1 spray under normal ambient conditions is smaller than 50μm at gas-liquid mass ratios (GLR) that are also smaller than other atomizers. High-speed visualization and droplet size measurements reveal relatively larger droplets by film breakup at low atomizing air mass flow rate. The prompt breakup mode induced at high atomizing air mass flow rate is responsible for generation of smaller sized droplet population clustered in chevron structures and desirable for ignition and flame stabilization. The strong dependence of viscosity of gelled Jet A1 on the gel mass flow rate and shear induced by micro air jets help in achieving similar spray characteristics as that of Newtonian ungelled Jet A1 at low GLR. Dimensional analysis of the breakup process yielded Ohnesorge number, momentum flux ratio, and GLR as possible correlating parameters for SMD and the experimental droplet size data of gelled Jet A1 sprays is reduced in the form of an empirical correlation.