Thermochemical protection of high temperature materials

An experimental investigation of cooling and heat protection of high temper ature objects, by a method based on endothermic chemical reactions is prese nted. The coolant is CH4 which reacts endothermally with CO2 and H2O. CO2 a nd H2O are supplied as hot products by hydrocarbon fuel combustion and are also used for heating the tested objects. The method is demonstrated by coo ling a hollow tube, and gas turbine blades. Significant wall temperature re duction, of DeltaT congruent to 300 K as compared to DeltaT=150 K with iner t nitrogen cooling, was obtained for wall temperature of T-w = 1050 K. It w as found that at lower temperatures the cooling effectiveness decreases due to the slow rate of the chemical reactions. At higher temperatures the coo ling rate remains constant due to diffusion limitations. Moire deflectometr y has been used for visualization and qualitative study of the density fiel d around the cooled objects. The cooling method is limited to fuel rich com bustion mixtures.