Optimization of Scallop Design for Cylinder Head of a Multi-cylinder Diesel Engine for Reduction of Combustion Deck Temperatures and Simultaneously Enhancing Combustion Deck Fatigue Margin.

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 varying operating conditions and thermal gradient generated because of operating conditions. The paper scope comprises an analytical and experimental study on the reduction of combustion deck temperature of a diesel engine through the 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 this Scallop, optimization is selected as a measure to make thermal fatigue crack-resistant cylinder head because changing cooling water jacket design will cause a 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 design modifications in cylinder head design. Since there is a material removal from combustion face hence there will be a reduction in fatigue 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 DOE for reducing temperatures and these should also simultaneously meet the required fatigue margins. FEA models 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 a thermal survey performed on both cylinder heads. Water jacket fatigue margins should be reduced as minimum as possible along with reducing combustion deck temperature. The average % reduction in fatigue margin was about 2.6% and the combustion deck margin was enhanced up to 6%.