This paper presents the design, structural analysis, structural test validation and risk assessment done by Cummins to evaluate the structural integrity of Light Duty engine cylinder head for a Medium Wheelbase (MWB) pick-up truck. Initially, Cummins used the 2.5L and 3.0L (4-cylinder) engines that have standard power ratings based on existing requirements, but rising market demands for more power, fuel efficiency, lower cost and weight, and future emission compliance led to customer requirements for 15% uprate for 2.5L and 22% uprate for 3.0L from the same base engine. The increase in power requirement possesses challenges on critical components, especially cylinder heads in terms of thermal and structural limits.
Multiple analysis led design iterations were performed using cutting edge CAE software such as Ansys, Dassault Systems fe-safe, and PTC Creo to ensure the structural integrity of the cylinder head under high thermal and mechanical loads, and to keep design margins within acceptable limits. A key feature identified through topology optimization was diagonal ribbing pattern on each cylinder, which is novel, and similar pattern can be applied to both new and existing engine platforms to enhance stiffness without major changes to the water jacket.
The Cylinder head was subjected to a long endurance test, which comprises of high thermal and mechanical loads under extreme operating conditions. After running for specified number of hours as per inhouse test requirements, the engine was stopped for magnetic particle inspection for any signs of fatigue failure.
No major cracks were observed on the 3.0L Cylinder head combustion face. However, a few cracks were observed on the 2.5L cylinder head combustion face at exhaust & intake bridges. Upon investigation, it was concluded that crack was due to high thermo-mechanical fatigue loads and hence further optimization was carried out on the cylinder head design. Furthermore, cylinder head gasket coolant orifice optimization is done to improve the coolant distribution to each cylinder. Thermal analysis showed a reduction in exhaust & intake bridge temperature within the acceptable limits. This paper captures the detailed design and structural analysis on 3.0L and 2.5 L diesel engine Cylinder head.