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An investigation on the effect of dwell time of split injection on a diesel spray evolution and mixture formation process was carried out. A commercial 7-hole injector were used in the experiment to eliminate the possible discrepancies on the spray with single-hole research injector. Laser absorption scattering (LAS) technique was implemented for the measurement of the temporal evolution of fuel evaporation and mixture concentration. The diesel surrogate fuel consists of n-tridecane and 2.5% of 1-methylnaphthalene in volume basis was used. The total amount of fuel injected was initially fixed to 5.0 mg/hole. A split ratio of 9: 1 in mass basis was selected according to the results obtained from a previous study. The dwell time was varied from 120 µs to a negative value of −50 µs. The effects of negative dwell time was not ideal for lean mixture formation when compared to zero or positive dwell time conditions.

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.