Pressure-Swirl Atomizers for DISI Engines: Further Modeling and Experiments

A combined two-phase CFD nozzle model and 1-D fuel injection system model is used to predict the flow development inside the discharge hole of a pressure-swirl atomizer connected to a common-rail based fuel injection system for DISI engines. The fuel injection model accounts for the transient pressure pulses developing inside the common-rail and the injector upstream of the nozzle tip and predicts the fuel injection rate through the nozzle. This is then used as input to a 3-D single-phase CFD model estimating the transient development of the swirl velocity inside the pressure-swirl atomizer, as a function of the geometric characteristics of nozzle. The predicted transient velocity distribution upstream of the needle seat flow passage is used as initial condition to a 2-D two-phase CFD model solving for the location of the liquid-gas interface using the ‘volume of fluid’ (VOF) method and thus, allowing estimation of the transient formation of the liquid film developing on the walls of the discharge hole of the pressure-swirl atomizer. Characterisation of the resulting spray was obtained experimentally by a CCD camera under atmospheric back pressure conditions; these images have revealed the temporal development of the spray structure during the early injection period which can be linked to the predicted two-phase flow development inside the pressure-swirl atomizer.