OS-E: 0020 Inline-4 Engine Head

The structural analyses of a cylinder head under various loading conditions can be accomplished by means of finite element analysis using OptiStruct. The results, combined with each analysis concerning the different operating processes of the engine, can be separated mainly into two parts.

Figure 1. FE Model

The capacity of gasket sealing mainly depends upon the pre-stressing of the bolts, which are the source of the maximum external loading on the inner structure of the cylinder head.

The location of the weakest contact pressure on the raised portion of the gasket can be transferred as a result of the effect of thermal stress or strain, which may cause the increase in pressure and escaping of the gas.

Based on the above use case, Nonlinear Static Analysis is demonstrated for the Altair inline-four engine block model, as shown in Figure 1. The key features such as 3D pretension bolts, gasket material modeling, friction contact and bore deformations are highlighted.
Note: There are a few orphan grids in the model, which may lead to some differences in contour results when the H3D results are plotted in HyperView. If results are different from what is illustrated in this example, then mask the orphan grids in HyperView and plot the contour again.

Model Files

Before you begin, copy the file(s) used in this example to your working directory.

Model Description

The analytical procedure could further be divided into three load steps by means of the superposition principle for simulating various operating processes of the engine, so the structural analysis are composed of the outputs of these three load steps.
FE Model
Element Types
The linear material properties are:
Young’s Modulus
21500 MPa
Poisson's Ratio
Direct Tensile Modulus
Transverse Shear Modulus
Figure 2. Details of the Boundary Condition and Gasket Material Loading and Unloading Curve

Assembly Loadings
The major percentage of the loading applied to the engine is the assembly loading. This mainly refers to the pre-stressing of the bolts, and it plays an important role in preventing gas from escaping from the internal part of the engine.
Thermal Loadings
In the case of thermal loadings, the nodal temperatures resulting from the prescribed thermal analysis are assigned to all corresponding nodes of the FEM model of the second cylinder head in order to calculate the thermal stress/strain of the cylinder head structure.
Figure 3. Gas pressure

The gas pressure created as a result of the firing of the spark plug is imposed on the surface of the combustion chamber. However, the magnitude of the gas pressure varies with different durations of the cycle. For the steady-state analysis, the average gas pressure is introduced into the loading conditions for the simulation here.
The nonlinear static analysis material properties are:
Case 1
Assembly Loadings
Applied pretension loading (41.25 KN) in head bolts
Case 2
Thermal Loadings
Lock pretension displacements
Apply temperature loading
Case 3
Gas Pressure
Lock pretension displacements
Continue temperature loading
Apply combustion pressure loading


Figure 4. Subcase 1: Displacement Contour

Figure 5. Subcase 1: Stress Contour

Figure 6. Subcase 1: Gasket Pressure and Sealing Status

Figure 7. Subcase 2: Displacement and Stress Contour

Figure 8. Subcase 2: Stress Contour

Figure 9. Subcase 2: Contact Pressure Contour

Figure 10. Subcase 3: Displacement Contour

Figure 11. Subcase 3: Stress Contour

Figure 12. Subcase 3: Bore Distortion Graph of 4th Cylinder (Calculation Using SimLab)