Silicon Carbide Evaporator Tubes with Porosity Gradient Designed by Finite Element Calculations

Gas turbine combustors with premix burners can reduce NO, emissions. In a new premix burner concept the evaporation of the liquid fuel and the burning zone are decoupled. The liquid fuel is sprayed onto the porous outer surface of the evaporator tube. The flowing air and the fuel vapor enter the tube where the combustion takes place The tube must be gastight on the inner surface Inside the tube the temperature is about 1500 °C, at the outer surface about 550 °C Previous work shows that application of porous silicon carbide (SiC) ceramics is rather promising. Due to the temperature gradient both during steady state and transient operation high thermal stresses develop in the tube. Four different design variations of porosity gradients are investigated, a two-layer concept without FGM and three continuous porosity gradients (linear, convex, concave) By comparing the local stress distribution with the local strength of the four different design variations, a favorable porosity gradient is found Only with this tailored porosity gradient the failure probability of the component can be kept on a tolerable level.