Optical detection of combustion zone movement in solid high-energy materials

Optical methods in infrared (IR) and visible (VIS) ranges for detection of combustion zone propagation in solid high-energy materials, such as pyrotechnic compositions inserted into pyrolytic graphite (pyrographite) tubes and ignited at one end by a CO$_2$ laser beam are presented. The pyrographite tube is used as a thermal management transducer enabling detection of combustion zone movement because of unique thermal conductivity anisotropy of pyrographite resulting in low thermal conductivity of the tube along its axis and high thermal conductivity along the tube radius. In the first method, an IR thermal camera is applied for detection of heat zone movement induced on the external side surface of the pyrographite tube by the combustion zone travelling inside the tube. According to the second method, a VIS camera and a thermochromic layer covering the external side surface of the pyrographite tube are used for visualization of heat zone movement registered as the color change boundary traveling along the thermochromic layer. The change in color of this layer is caused by its thermochromic substance response to heat delivered by the heat zone. As thermochromic substances, leuko dyes or chiral-nematic liquid crystals are used. These methods seem to be particularly promising for continuous measurements of burning rates of solid high-energy materials, such as solid rocket propellants and pyrotechnic compositions.