Thermomechanical Stress Analysis of Novel Low Heat Rejection Cylinder Head Designs 930985

High thermal stresses in the cylinder heads of low heat rejection (LHR) engines can lead to low cycle fatigue failure in the head. In order to decrease these stresses to a more acceptable level, novel designs are introduced. One design utilizes scallops in the bridge area, and three others utilize a high-strength, low thermal conductivity titanium faceplate inserted into the firedeck (combustion face) of a low heat rejection engine cylinder head. The faceplates are 5mm thick disks that span the firedeck from the injector bore to approximately 10mm outside of the cylinder liner. Large-scale finite element models for these four different LHR cylinder head configurations were created, and used to evaluate their strength performance on a pass/fail basis.

The complex geometry of this cylinder head required very detailed three-dimensional analysis techniques, especially in the valve bridge area. This area is finely meshed to allow for accurate determination of stress gradients. The completed three-dimensional models for the various configurations differ, but all are comprised of over 39, 000 elements and over 47, 000 nodes, resulting in over 145, 000 simultaneous equations to be solved in the stress analysis model. These equations can be solved in a timely manner only through the use of high performance computing.

In our earlier analytical work concerning a finite element methodology for analysis of minimum cooled low heat rejection (LHR) engine cylinder heads, it was concluded that thermal stresses were higher than yield over a significant portion of the cylinder head. The aim of this paper is to show how finite element analysis (FEA) and analytical screening, facilitated by high performance computing can be used as an effective tool in understanding some of the causes of these thermal stresses, and aid in developing designs to help reduce them.