Visualization of aluminum dust flame propagation in a square-section tube: comparison of schlieren, shadowgraphy and direct visualization techniques

Abstract : This paper presents the results of aluminum dust flame propagation inside a vertical prototype of 700 mm height and 150 × 150 mm square cross section. The study considers three visualization techniques. At first, direct visualization is employed to record the flame light with high speed camera. Special attention is given to collect images without saturation. This is especially important with aluminum flames as they are very luminous. To ensure that the exact delimitation of the flame is well defined, two additional optical techniques have been implemented: schlieren and shadowgraphy. For each explosion test, these three techniques were used simultaneously to compare the flame propagation and the burning velocity. The first one corresponds to the flame speed in the laboratory referential, determined from the obtained images, while the burning velocity corresponds to the consumption rate of the reactants by the flame front. The method used for the determination of burning velocity from the images obtained is exposed. A pulsating behavior of the light emitted by the flame is observed with the direct visualization technique. This behavior confused the determination of the flame front. This contour is easier to define with shadowgraphy images. Nevertheless, results of flame front propagation velocity are close for each technique. Burning velocity is then determined only from direct visualization and shadowgraphy images, to avoid uncertainties due to flame contour detection from schlieren images. Again, results of burning velocity are fairly close for both techniques.