Diesel spray injected into an atmosphere with high pressure and high temperature becomes, within a few milliseconds, a transient two-phase flow, entraining the surroundings. The motion of the surroundings is a significant phenomenon for the mixing of droplets and the entrained surroundings, and this phenomenon determines the combustion processes of diesel spray. In the experiment presented here, motion was visualized by the smoke-wire method. Moreover, the movement around a two-dimensional steady water spray (two-phase flow), and an unsteady water jet (single-phase flow), were also tested to generlize motion in the surroundings of the diesel spray. It was found that the entranining angle, the coefficient of entrainment velocity, and the entrainment coefficient of diesel spray at penetration part (where it shows characteristics of steady flow) are similar to those of two-dimensional steady water spray and the unsteady water jet, and that the ratio of the volume of the entrainment to the total volume of either the spray or the jet is nearly equal to 0.5.
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