Generalised scattering imaging laser technique for 2-D characterization of non-isothermal sprays

Optical techniques based on the properties of the scattered light are widely utilized to study liquid fluid sprays. However, these techniques generally require the knowledge of the optical properties of the liquid forming the droplets. This limits their use in the study of sprays in non-isothermal regime where unknown variations of the optical properties occur. In this paper the application of the generalised scattering technique, GSI, to the characterization of spray droplets in isothermal, evaporating and burning regimes is discussed. GSI is a two-dimensional imaging technique able to measure the size of droplets with a maximum uncertainty of 4%, even if no information is given on the properties of the fluid. The method is based on a peculiar experimental configuration where the imaging system is set in out of focus condition. The peculiar string-shape of the images allows the application of GSI to moderate dense spray with a droplet concentration as high as several thousands droplets per cubic centimeter. This technique being not sensitive to the refractive index of droplets is particularly prone for studying sprays in combustion. By using the GSI method, the evaporation and combustion of isopropyl alcohol droplets was successfully studied and the relative rates determined.