Taylored binarization of spray shadowgrams for morphhology investigation

One of the simplest and most used diagnostic systems for sprays is, out of doubt, flash shadowgraph. The diagnostic technique based on the principle of flash shadowgraph provides images in which a value on a brightness level scale is associated to each pixel. This value accounts for the amount of light, emitted by the source and crossing the spray. As a consequence of diffusion and absorption phenomena taking place in correspondence of the liquid-gas interface of the spray droplets, light attenuation occurs and the digital camera receives a damped signal. Light signal attenuation not only depends on real and imaginary part of the refraction index, but it gets stronger as droplet size and concentration increase. The overall amount of liquid-gas interface intercepted from source to detector contributes to light extinction, therefore it is not possible to get information about individual droplets. In this paper the chance to achieve quantitative insight of a dense spray from shadowgraphic images (or shadowgrams), collected by simple, affordable diagnostic setup, is investigated.