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A comparison of spray characteristics between single-hole and multi-hole injectors were conducted under same rail pressure condition of 100MPa or similar injection rate profile condition. The same injection rate profile was achieved by adjusting the rail pressure. Laser absorption scattering (LAS) technique was implemented for measuring the mixture concentration distribution. Injection quantities of 2.5mg and 0.5mg were selected to realise quasi-steady state and transient spray, respectively. In case of quasi-steady spray and same rail pressure condition, the difference in terms of mixture distribution between single-hole and multi-hole injector was not significant under 2.5mg condition. This is because the quasi-steady spray played dominant role over the injection process. However, in case of transient spray condition, single-hole injector showed the longer vapor penetration but smaller spray angle than that of multi-hole injector. Nevertheless, the single-hole injector showed the faster lean mixture formation after start of injection than that of multi-hole injector. However, at the end-of-injection (EOI) timing, the single-hole injector showed slower evaporation rate. The air entrainment characteristics of both injectors were assessed using a 1D spray model. The propagation speed of the relative entrainment rate was greater for single-hole than that of multi-hole injector. It contributed in leaner mixture formation for single-hole injector after EOI. Under the similar injection rate profile condition, the vapor penetration was almost identical for both injectors. However, multi-hole injector showed the wider spray angle than that of single-hole injector. Therefore, the multi-hole injector showed the leaner mixture distribution and faster evaporation rate than that of single-hole injector. In summary, for the transient spray condition, the single-hole injector was advantageous on the air entrainment under the same rail pressure, whereas the multi-hole injector was advantageous under similar injection rate profile.
