Why is the cylinder head warping? FEA has evidence

The U.S. military has so many diesel-powered vehicles, it's natural for them to want to improve their efficiency. The solid model of the cylinder shows the detail necessary for the thermal and stress simulations. Steady-state heat-transfer analysis, conducted with Algor FEA software, revealed high temperatures between the two exhaust ports. This simulation was the first part of a multiphysics analysis. The linear static-stress analysis predicted thermal stresses well beyond the material's yield point between the two exhaust ports, especially on the inner face in the inset. Columbus, Ind., used multiphysics FEA software from Pittsburgh, to study the thermal and structural behavior of a prototype diesel-engine cylinder head designed for lower heat rejection and increased power density. In the prototype, temperatures on a stainlesssteel cylinder head were measured at 1,600°F, almost twice the normal operating temperature of 800 to 900°F. Distortion of the cylinder head at such high temperatures was causing leaks in valve inserts and the head gasket. Finite-element analysis was needed to evaluate the head's design and materials, and verify that high temperatures were, in fact, causing the leaks. Vishwas Bantanahal, an engineer at Adiabatics, began with a Pro/E model of the cylinder head and six washers under the bolt heads. He used the FEA developer's InCAD to capture the geometry and create a 3D finite-element mesh. “This direct CAD to CAE data exchange is easier than other methods, such as an intermediate file format,” he says. Small holes and cuts were suppressed to prevent stress concentrations and for a better understanding of the overall stress distribution. Bantanahal also refined the mesh around the holes and fillets. The model was set up for a steady-state heattransfer analysis. AISI 410, a stainless steel, was specified for the cylinder head and carbon steel for the washers. Bantanahal modeled the washers as well