Shock and wave dynamics in fuel injection systems

Due to the exceptional high inlet pressure Lip to 2000 bar flow dynamics and efficiency of modern injection systems are controlled by high frequency wave dynamics of the compressible liquid flow. Corresponding to alternating shock and expansion waves the liquid fluid evaporates and recondenses instantaneously. Here we present CFD simulations of the time accurate evolution of cavitating flows in 2-D plane and in 6-hole injection nozzles with focus on the wave dynamics just after initialisation of the flow and within the time scale Delta t <= 10(-4) S of pilot and multi-point injection. Due to shock reflections at the bottom of the sack hole the instantaneous maximum pressure increases more than three times higher as compared with the prescribed pressure at the nozzle inlet. For instance, in case of an inlet pressure of 600 bar the maximum pressure in the sack and therefore ahead of the nozzle bore holes reaches about 2100 bar. It is quite reasonable that this amplification of the pressure effects the evolution of the convective flow and therefore the mass flow through the nozzle bore holes.