Pyrolysis in the liquid phase inside single droplets of light oil studied with laser scattering methods

A new optical set up for the measurement of the angular distribution of the polarized components of light scattered by single droplets has been realized. It allows the simultaneous determination of the size, velocity and complex refractive index of the droplets. The vaporization and chemical transformation in the liquid phase have been studied with this technique in the temperature range between 20°C to 700°C for arrays of droplets of pure hydrocarbons and commercial light oils. It was found that droplets composed by commercial blending became opaque in the visible (» = 514.5 nm) while those composed by pure compounds exhibit only a vaporization without reaction in the liquid phase. This effect is attributed to a class of aromatic compounds with polar characteristics and it is qualitatively similar, although less relevant, to that which takes place inside droplets of heavy oils at high temperature. The increase of absorbivity of heated up droplets has been detected also in spray in burning conditions and the effect may have relevance in the formation of particulate phase during combustion.