Dipartimento d'Ingegneria

Background –  The shape of fuel injection ramps affects spray penetration and mixing process, especially with short multiple injection strategies [1] as generally used in direct ingection engines. It has been shown that after an injection pulse fuel dribbles can be produced, and a significant amount of ambient gas is also ingested in the nozzle sac depending on factors like ambient back pressure, hole sizes, etc. [2,3]. The start of a new injection event is consequently affected by the presence of residual gas in the sac. During the first 100 µs after Start-of-Injection (aSOI) liquid penetration is shorter and evaporation rate is altered [1]. This work reports investigations on diesel spray transients, accounting for internal nozzle flow and needle motion, carried out at Argonne National Laboratory (ANL) [8]. LES of end-of-injection and start-of-injection processes have been carried out on a single hole injector, trying to link the phenomena and provide insights in to the physics.