Detonation and shock-induced breakup characteristics of RP-2 liquid droplets

Abstract

The deformation and breakup characteristics of liquid rocket propellant 2 (RP-2) droplets are experimentally investigated in a shock tube. The RP-2 droplets are subjected to a weak shock wave, a strong shock, and a detonation wave to deduce the impacts of high-speed and supersonic reacting flows on droplet deformation and breakup. High-speed shadowgraph and schlieren imaging techniques are employed to characterize droplet morphologies, deformation rates, and displacement of the droplet centroid. The results reveal that the transition from a shock wave to a detonation suppresses the deformation of the droplet and augments small-scale breakup. A shift in dominant breakup mechanisms is linked to a significant increase in the Weber number due to an increase in flow velocities and temperatures when transitioning to the detonation case. The experimental data are combined with a droplet stability analysis to predict the “child” (or fragments of the initial “parent” droplet) droplet sizes of each test condition. The child droplet size is shown to decrease as the flow regime transitions toward a detonation. An analytical mass stripping model was also used to determine that the total mass stripped from the parent droplet increased when approaching supersonic reacting conditions. The child droplet sizes and mass stripping rate will ultimately influence evaporation timescales and ignition in supersonic reacting flows, which is important for the development of detonation-based propulsion and power systems.