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 2019-01-0273
A comparison of spray characteristics was conducted between single- and multi-hole injectors. Both macroscopic and microscopic imaging was applied to observe the penetration, the spray angle, and the dispersion (spray cone) angle at the vicinity of the nozzle. Simulations using a commercial software (AVL FIRE) was conducted to reveal the internal flow inside the sac volume. Laser absorption scattering (LAS) technique was implemented for measuring the mixture concentration. The vapor penetration was greater for single-hole than that of multi-hole due to faster 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 term at the nozzle exit induced by the turbulent internal flow. The spray of both injectors at their corresponding end-of-injection (EOI) timings showed that, the evaporation ratio (vapor mass / total mass) for single-hole injector was lower than that of multi-hole injector due to its narrow spray angle and dense liquid core. However, 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 EOI timing for single-hole injector, the higher spray momentum of single-hole injector enhanced the air entrainment process afterwards, and resulted in faster lean mixture formation compared to that of multi-hole injector. The injection pressure was varied in order to match the injection rate of both injectors, so as to match the spray momentum and the penetration. In such case, the mixture formation was worse for single-hole injector than that of multi-hole. Higher dispersion angle of multi-hole injector assisted faster lean mixture formation process.