To further understand fundamental mechanism of mixture formation in diesel engines, the high speed CMOS camera with a long distance microscopy and the high frequency diode laser were employed to record the near-nozzle field injection processes under both non-evaporating and evaporating diesel-like conditions. At the room temperature condition, small droplets were observed at the spray tip before the end of injection and along the jet boundaries during the quasi-steady injection process. During the end-of-injection transients, while there were some poorly-atomized large droplets and ligaments with low penetration velocity, the mist-like tiny droplets suspending at the vicinity of the nozzle dominated the droplet number distribution. Under the 4.0 MPa and 900 K. ambient condition, no droplets and ligaments at the spray tip and along the jet boundaries were clearly observed before the end of fuel injection. During the end-of-injection transients, owing to the low penetration velocity and sparse distribution of the fuel, some droplets were observed, indicating the surface tension confining the liquid to a sphere shape; at the same time, however, some cotton-like structures were also observed, implying the diminishment of the surface tension of the fuel.
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