“…Moreover, the swirling flow conditions prevailing due to the complex recirculation of the flow inside the injector's sac volume, also induce cavitation at the core of the formed vortices (so-called string cavitation, see selectively [30,31,32,33]). Notwithstanding, during the dynamic movement of the injector needle valve, needle seat cavitation has been observed [32] and substantial cavitation in the nozzle's sac volume at the end of the injection has been numerically predicted [34,35,29]; distinguishing vapour from ingested air is not straightforward from experimental observations.…”