Internal Fuel Flow, Near-Field and Far-Field Spray Evolution, and Mixture Formation Characteristics of Diesel Injectors - A Comparison between Multi- and Single-Hole Injectors

A comparison of spray characteristics was conducted between single- and multi-hole injectors. A commercial software (AVL FIRE) was used to investigate the internal flow inside the sac volume, as well as the initial spray behavior at 1 mm downstream of the nozzle exit. Microscopic imaging was applied to observe the spray dispersion angle (spray cone angle) at the vicinity of the nozzle. Laser absorption scattering (LAS) technique was implemented for measuring the mixture concentration. Three injection quantities, namely 0.5, 2.5, and 5.0 mg/hole, were selected to observe the differences between transient and quasi-steady spray. The vapor penetration at the initial stage of the injection was greater for single-hole than that of multi-hole injector due to faster fuel pressure build-up process inside the sac volume. The dispersion angle was higher for multi-hole injector than that of single-hole during the transient period, due to higher radial velocity vector at the nozzle exit induced by the turbulent internal flow and the vortices. For injection quantity of 0.5 mg condition, lean mixture formed faster for single-hole injector due to its greater penetration right after start of injection (SOI). Despite the low evaporation ratio at end of injection (EOI) timing for single-hole injector, the higher spray momentum of single-hole injector and additional air entrainment wave after the EOI resulted in faster lean mixture formation compared to that of multi-hole injector. Mixture formation process was similar for large injection quantity of 2.5 mg, as the both injectors entered into the quasi-steady state injection.