A characterization of the spray evolution by dual-mode phase doppler anemometry in an injector of liquid-propellant thruster

Spray characteristics of an injector employed in the 5 Newton-class of liquid-propellant thruster are addressed with an evolutionary feature of droplets. Information for the droplets is obtained through Dual-mode phase Doppler anemometry (DPDA) measurement in terms of the velocity, diameter, number density, and turbulent intensity. In addition, instantaneous images for the macroscopic view of spray are supplemented by flow visualization technique using laser sheet. It is demonstrated by the investigation of spray images that the injector under consideration meets an angular injection requirement at all of the injection pressures specified. Spray shedding is also featured with a schematization of the frozen images. Dynamic behavior of spray droplets and their atomization evolution along the geometric axis of injector-nozzle orifice with varying injection pressures are scrutinized by depicting the cumulative droplet populations mapped onto a velocity-diameter domain. The evolutionary behavior is further authenticated on the basis of the distribution for number density and turbulent intensity of droplets. It is inferred that the higher injection pressure generates the smaller droplets undergoing the greater deceleration along the spray stream due to the augmented Reynolds number and Weber number. Even though spray characterization of the current type of injectors is to be inevitable to their performance estimation at the design stage, it has never been reported to date. It is expected that the present results will be able to contribute to the appreciation of injector performance and to the design engineering of brand-new thrusters as well.