Coupled Simulations of Nozzle Flow, Primary Fuel Jet Breakup, and Spray Formation

Abstract

Presented are two approaches for coupled simulations of the injector flow with spray formation. In the first approach the two-fluid model is used within the injector for the cavitating flow. A primary breakup model is then applied at the nozzle orifice where it is coupled with the standard discrete droplet model. In the second approach the Eulerian multi-fluid model is applied for both the nozzle and spray regions. The developed primary breakup model, used in both approaches, is based on locally resolved properties of the cavitating nozzle flow across the orifice cross section. The model provides the initial droplet size and velocity distribution for the droplet parcels released from the surface of a coherent liquid core. The major feature of the predictions obtained with the model is a remarkable asymmetry of the spray. This asymmetry is in agreement with the recent observations at Chalmers University where they performed experiments using a transparent model scaled-up injector. The described model has been implemented into AVL FIRE computational fluid dynamics code which was used to obtain all the presented results.

Investigation of the Flow Pattern inside a Diesel Engine Injection Nozzle to Determine the Relationship between Various Flow Parameters and the Occurrence of Cavitation

“…Thus, the measurement of the momentum flux can be combined with the injection rate to derive the velocity at the nozzle exit [7] [8]. Also, the influence of nozzle geometry on the internal flow characteristics of a diesel injector has been carried out with a simulation analysis [9]- [12]. The simulation studies confirm the tendency observed in experiments, that the nozzle geometry significantly influences the inner flow characteristics.…”

Numerical modelling of diesel spray using the Eulerian multiphase approach

“…Here, the spray contours were determined by the limiting threshold values for the liquid volume fraction and the vapour mass fraction. More details about the determination process of the limiting threshold values can be found in [40]. In our work, the liquid tip penetration was defined as the furthest distance of the liquid phase where the total liquid volume fraction accounts for 0.1% of the control volume.…”

“…The coefficients used within the atomisation models are presented by Eqs. (14)- (17), whilst the break-up model details are described in [40]. The definition of the harmonic turbulent/aerodynamic time scale combination is shown in [34].…”

On the Link between Diesel Spray Asymmetry and Off-Axis Needle Displacement

“…The state of bubble diameter is a function of position and time (poly-dispersed diameter); coalescence due to turbulent random collisions, breakup (induced by turbulent impact) and bubble generation due to cavitation are the mechanisms taken into account. The complete mathematical description of this approach in the modeling of multiphase nozzle flow has been published and can be found in [44,45]; these authors also report the model validation against several reference flows.…”

“…To allow the comparison among the holes, the results of the nozzle CFD model have been lumped in non-dimensional parameters that qualify the flow at each outlet section [45]. In the adopted scheme, Equation (16), the liquid-phase mass flow rate (m r ) passes through an effective area (A e ) with a uniform velocity (v e ); thus, vena contracta and cavitation affect the flow reducing the geometrical area (A g ) to the effective one (A e ).…”