Failure and thermo-mechanical stress analysis of the exhaust valve of diesel engine

• In a diesel engine the fatigue failure of the exhaust valve was occurred.
• The crack origins were not covered by material defect and corrosion products. The valve was not overheated.
• Results of work showed that small tension stresses were observed in the valve during work of the engine without disturbances.
• The observation of another valve from damaged engine head showed that the carbon deposit was located on the valve face.
• Results of stress analysis of the valve with carbon deposit showed that large bending stress in the valve stem was occurred.
• Large amplitude of bending stress in the valve with the carbon deposit was a main reason for premature failure of the valve.

In this work the failure analysis of the exhaust valve of diesel engine was performed. Visual examination of damaged engine parts showed that on the fracture of exhaust valve the beach marks, typical for fatigue failure were observed. Additional observations of the crack initiation zones indicated that the crack origins were not covered by material defects or corrosion products. In order to explain the reason of premature valve damage, the non-linear finite element analysis was utilized. The discrete model of simplified valve system composed of the valve guide, the poppet valve and the seat face was defined. In numerical analysis both the mechanical force arising from the valve spring and also the thermal load resulting from the non-uniform temperature field were defined. The results of nonlinear static analysis showed that in the engine without any disturbances, the maximum principal stresses in the critical zone of the valve have low values. The examination of another (non-defected) valve from damaged engine head indicated that irregular carbon deposit was located on the valve face. The results of stress analysis performed for the valve with the carbon deposit showed, that in the valve stem a high bending stresses were occurred.