Thermo-mechanical behaviour of an injection nozzle for a cogeneration system based on the aluminum/water reaction

The thermal behaviour of an injection nozzle for a prototype combustion chamber of a cogeneration system based on the reaction of liquid aluminum and water steam, is analyzed. The heat released by the oxidation of aluminum with water is exploited for super-heating the vapor of a steam cycle and simultaneously producing hydrogen. The only by-product is alumina, which can be transformed again into aluminum. From a thermo-mechanical point of view, the most critical part of the system is the injection nozzle, located at the end of a graphite pneumatic needle valve. The head of the injector is made by titanium and includes a Titalox ceramic nozzle characterized by a 0.5 mm calibrated hole. After a warm up cycle, the injector reaches temperatures of the order of 1000°C. During the subsequent cool-down phase, the different strain rates of the two materials could lead to mechanical failure. In this work, the heating and cooling transients of the injection zone are simulated by a Finite Volume approach. Temperature distributions are then transferred to a Finite Element structural solver in order to verify the resulting stresses. Temperature measurements taken during preliminary experimental tests provide a qualitative assessment of the reliability of the numerical predictions.