Hydrogen low-pressure direct injection: 3D-CFD hollow cone injector model, flow and mixing analysis

A three-dimensional unsteady Reynolds-averaged Navier-Stokes (URANS) modelling framework was employed to study the flow and mixing characteristics of a hydrogen low-pressure direct-injection process using a hollow-cone injector. The hollow-cone injector model was validated with experimental data, and a sensitivity analysis of numerical mesh, turbulence model, turbulent Schmidt number, and Courant-Friedrichs-Lewy number was carried out. Then, the local flow, mixing, and turbulence characteristics were investigated first by varying the injection pressure at a constant chamber pressure, then by varying the injector needle lift at a constant fuel mass. The results showed that increasing the fuel injection pressure at a constant needle lift resulted in increases in total injected fuel mass, axial penetration, radial penetration, and turbulent kinetic energy. Furthermore, elevating the needle lift while maintaining a constant fuel injection pressure also resulted in increases in total injected fuel mass, axial and radial penetrations, and turbulent kinetic energy. Analysis of the balance between needle lift and injection pressure, with fixed total injected fuel mass, shows that the case with 85 μm needle lift and 20.7 bar injection pressure exhibits increased axial penetration, while the case with 135 μm needle lift and 12.68 bar injection pressure e demonstrates increased radial penetration. The scenario involving a 35 μm needle lift and 51 bar injection pressure exhibits, on average, 35% and 20% higher turbulent kinetic energy compared to the 85 μm and 135 μm scenarios, respectively, and reaches the highest turbulent kinetic energy levels of 13 m 2 /s 2 , while the other two scenarios remained at 7.5 m 2 /s 2 ; this represents an increase of approximately 75%. Additionally, in this case, distinct areas of elevated vorticity with strong shear layers and substantial jet momentum were observed while exhibiting minimal jet disturbance.