Potential of a jet-induced shock wave to influence an upstream droplet cloud in compression-ignition engines using multiple injection strategies

High-pressure diesel-fuel sprays have been shown to emit shock wave under certain conditions, while the advanced injection strategy used in internal-combustion engines involve multiple injections taking place within a short time frame. Experimental study of double injection has shown in two instances that the first fuel-spray cloud could be accelerated before the arrival of the second fuel spray. Herein, it is hypothesized that a shock wave emitted from an injection interacts with the fuel-spray cloud of a preceding injection and is responsible of a push-away mechanism on the first droplet cloud reported on in the literature. In this context, the shock waves emitted by fuel-spray jets with a commercial 5-hole diesel injector injecting into a pressure vessel were characterized with schlieren visualizations and dynamic pressure measurements taken with single- and double-injection strategies. The experimental results confirm the shock presence based on schlieren measurements. The measured shock conditions show a different shock topology from most shock-tube experiments as the expansion wave closely followed the shock front, resulting in a thin shocked region and a short duration of the droplet exposition to the post-shock gas conditions. Experimental measurements were then used as initial conditions in a 1D multiphase simulation model allowing simulation of the shock-wave interaction with the droplet cloud under engine-related conditions. The model was used to conduct a parametric study on the droplet-cloud characteristics and showed that, as the cloud density increased, the shock intensity and droplet-induced velocity decreased. Finally, the model was used to illustrate that the push-away interaction mechanism could be explained by the shock wave-fuel-droplet-cloud interaction.