A mathematical model for schlieren and shadowgraph images of transient expanding spherical thin flames

Optical behavior of spherical flames is investigated using both Schlieren and shadowgraph methods. A mathematical model has been developed to predict the intensity of refracted light beams interacting with a transient expanding thin flame. Experimental facilities have been built to visualize transient expanding spherical flames. The facilities include a cylindrical chamber with two end glasses for optical observation. Shadowgraph and Schlieren pictures of flame propagation have been taken using a high-speed charged coupled device camera. Experimental results are in very good agreement with those predicted by the theoretical model. Schlieren and shadowgraph techniques have also been used to view smooth, cracked and cellular flames; these techniques will be useful in future in studies to determine the stability of propagating flame.