DYNAMIC STRESS BEHAVIOR IN CATALYTIC COMBUSTORS

Dynamic stress behavior during catalytic combustion of methane has bee n simulated under transient warm-up, cool-down, and cyclic conditions. The numerical model combines a two-dimensional solution to the transp ort equations, solution of an energy balance on the monolith wall, and the NIKE3D structural analysis code to predict thermal stresses. The model also includes a detailed heterogeneous kinetics model for a prop rietary palladium oxide (PdO) catalyst, but the model ignores gas-phas e reactions. Results illustrate that thermal stresses as high as 630 M Pa can form during transient operating modes, which risks structural f ailure of the ceramic monolith. The maximum computed thermal stress co ncentrations occur near the inlet of the monolith. Peak transverse str esses (which act to form axial cracks) typically form near the inlet a nd centerline of the monolith structure, while peak axial stresses for m near the edges of the flat plate that represents the monolith struct ure. Increasing the preheat temperature of the incoming fuel and air m ixture lessens the peak thermal stress. To a first approximation, the magnitude of the peak transverse stress during any transient cycle con sidered with our model can be estimated from the maximum value of the gradient in the computed temperature profiles.