Thermal fatigue crack failure is becoming the most important aspect in modern cylinder head design as modern engines are striving towards higher peak cylinder pressures. Thermal cracks are developed in the cylinder head due to thermal gradients generated because of operating conditions. Paper scope comprises analytical and experimental study on reduction of combustion deck temperature and enhancing combustion deck fatigue margin of a diesel engine through introduction of scallop on the combustion face.
There are methods such as cooling jacket optimization, faceplate insertion, scallops and other measures to reduce the temperatures on the combustion deck. Among these Scallop optimization is selected as a measure to make thermal fatigue crack resistant cylinder head because changing cooling water jacket design will cause change in castings for the cylinder head which may increase the development cost whereas introducing scallop will require just extra machining feature which does not require any major casting design modifications in cylinder head design. Since there is a material removal from the combustion face hence there will be reduction in High cycle fatigue (HCF) strength in water jacket location as well, therefore it is a trade-off between temperature reduction and fatigue strength if scallop is introduced.
Optimum scallop dimensions will be obtained from Design of Experiment (DOE) for reducing temperatures and these should also simultaneously meet the required water jacket HCF fatigue margins. Finite Element Models (FEA) will be calibrated through thermal mapping performed on the cylinder head to increase the accuracy.
Initially, Baseline and concept cylinder head models were analyzed through FEA and models were calibrated by thermal survey performed on both cylinder heads. Water jacket HCF fatigue margins should be reduced as minimum as possible along with reducing combustion deck temperature. Maximum % reduction in water jacket HCF fatigue margin was ~6.5% and combustion deck fatigue margin was enhanced up to 6%.