Numerical Simulation of Hollow-Cone Sprays Interacting with Uniform Crossflow for Gasoline Direct Injection Engines

The interaction of fuel sprays with in-cylinder air flow is crucially important for the mixture preparation and subsequent combustion processes in gasoline direct injection (GDI) engines. In the present work, the experimentally validated computational fluid dynamics (CFD) simulations are performed to study the dynamics and physical insight of hollow-cone sprays interacting with a uniform crossflow. The basis of the model is the standard Reynolds-averaged Navier-Stokes (RANS) approach coupled to the Lagrangian treatment for statistical groups (parcels) representing the physical droplet population. The most physically suitable hybrid breakup models depicting the liquid sheet atomization and droplet breakup processes based on the linear instability analysis and Taylor analogy theory (LISA-TAB) are used. Detailed comparisons are made between the experiments and computations in terms of spray structure, local droplet diameter and velocity distributions. The computational results reveal the important features of the hollow-cone fuel spray in crossflow: the spray axis deflection by the crossflow is identified; the small droplets in the spray are displaced by the crossflow and transported to the downwind side; the vortical structure of the spray on the impacted side is significantly suppressed; there is a blockage effect of the spray on the crossflow in the near-nozzle field, and the counter-rotating vortex pair (CVP) owing to the interaction between the crossflow and the fuel spray is clearly captured. Furthermore, test cases with different crossflow velocities and at elevated ambient temperature are carried out to study the effects on spray characteristics and mixture formation. With higher crossflow velocity, the results show that the development of CVPs become slowly along the flow field, the secondary breakup is enhanced, and therefore a more uniform spray with smaller mean droplet diameter is produced. Additionally, the cumulative fuel vapor mass increases and the low temperature field within the normal spray cone shrinks, which means that the fuel/air mixing, fuel vaporization, and air utilization could be improved in the combustion chamber of GDI engines.

Computed droplet size distribution at various crossflow velocities (a) pinj=3.0 MPa, Qinj=24.2 mg, pa=0.1 MPa, Ta=312 K, Ua=11 m/s; (b) pinj=8.0 MPa, Qinj=39.8 mg, pa=0.1 MPa, Ta=312 K, Ua=11 m/s.

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