Preheated liquid jet breakup dynamics in a twin-fluid injector

This paper aims to investigate the influence of liquid preheating on primary jet breakup in a coaxial twin-fluid injector. The injector was operated over a broad range of conditions. Three different liquid injection temperatures were realized. Time-resolved shadowgraphic images of the liquid jet breakup were recorded using a high-speed camera. The images were analysed to measure various parameters including effective jet diameter at the nozzle exit, the mean and fluctuations of the jet breakup length, as well as time-scale of Kelvin–Helmholtz (KH) instability. The jet flapping instability was characterized by POD analysis. Even moderate liquid preheating is found to strongly influence the jet breakup behaviour. Different trends of the measured jet breakup parameters with respect to liquid injection temperature are identified depending on gas-to-liquid momentum flux ratiM, being larger or smaller than about 6. In this context, the roles of KH and flapping instabilities are explained.