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 document, then mask the orphan grids in HyperView and then plot the contour again.

Model Files

Refer to Access the Model Files to download the required model file(s).

The model file used in this example includes:

NLSTAT_ALTAIR_PWT.zip

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
CHEXA
CTETRA
The linear material properties are:
MAT1
Young’s Modulus
21500 MPA
Poisson's Ratio
0.3
MGASK
Direct Tensile Modulus
0.001
Transverse Shear Modulus
12000


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

Results



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)