This research is made of two experiments. First, the suspended droplet experiment is used to observe the effects of a nitro-paraffin-based additive on the physical and chemical mechanisms involved in the evaporation of diesel drops. The results show that the fuel additive has no significant effect on the heat transfer behavior and fuel vaporization rate of the diesel droplets in an inert high-temperature ambient. Following this outcomes, no additive was used in the main part of this investigation, which consist of freely falling drop-streams of diesel fuel with different initial spacing, injected in a high-temperature, convective environment; to evaluate the effects of drop spacing on the ignition, flame transition, drop evaporation rate and soot formation.
The flame of diesel fuel drops for Si ≧ 10 was initially located ahead of the drop, then became a spherical envelope flame and finally moved behind the drop burning as a wake flame. Combusting diesel fuel drops were found to be sooty. Drop streams with Si = 3 and 5 were surrounded by a bulk flame tube and produced large agglomerates of soot. The effect of drop spacing on the evaporation rate was not monotonic. From Si = 3 till Si < 40, the vaporization rate was increasing. For Si > 40, the drop evaporation rate decreased with Si. For some case, the flame streaks from the diesel drop streams for Si ≧ 40 showed some interesting phenomena proper of multi-component fuels, like flame shrinkage and disruptive burning. The initial drop spacing affected the soot tendency and drop evaporation rate.

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