Experimental study on microscopic and macroscopic characteristics of diesel spray with split injection

The microscopic and macroscopic characteristics of diesel spray with split injection strategy were systematically investigated by employing ultra-high speed imaging in the near-field, high speed imaging and Phase Doppler Particle Analyzer (PDPA) techniques. It was found that for single injection there were four stages for the development of spray penetration, largely depending on injection pressure and ambient pressure. With split injection strategy, the "wake driving force" caused by higher speed of the wake of the first injection than that of periphery gas tended to distort the second split injection, whereas the 'air driving force' caused by the first split injection tended to make the second plume symmetric. Furthermore, the second split injection showed lower macroscopic penetration and spray area during the initial stage but higher macroscopic penetration and spray area at the later stage than the first injection. In addition, higher injection pressure lead to better dispersion and smaller droplets. The strong collision (both primary collision and secondary collision) caused larger droplets for split injection than for single injection. Lower effective injection pressure due to lower injector opening for split injection strategy was believed to be partly responsible for the larger droplet sizes.