Causal Investigation of Heavy-Duty Diesel Engine Structural Limitations to Peak Cylinder Pressure, 03-R9670

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Principal Investigators
Marc Megel
Mark Tussing
Barry Westmoreland

Inclusive Dates:  11/17/06 – Current

Background - Advances in emissions technology, fuel economy and power levels of modern heavy-duty diesel engines have increased operating peak combustion pressures to levels at or near the structural limits of the design of the engines. The relationship between design parameters and structural performance for geometrically complex engine components, like cylinder heads or cylinder blocks, is not well understood. Future improvements in the performance of the existing fleet of heavy-duty diesel engines will require an increase in the structural capability of the engine design. This program is targeted at gaining a clear understanding of the relationship between the structural performance and the key design parameters for heavy-duty diesel cylinder heads.

Approach - The approach consists of demonstrating analytically the limitation of current designs at increased combustion pressures, and then an analytical study of the effects and interactions of basic cylinder head design features as related to the structural durability of the cylinder head. The parameters studied will include both geometric features and material properties. The study will utilize finite element analysis (FEA) as the primary means of assessing structural performance. The approach is utilizing design of experiments to assess the main effects and interactions between the parameters of interest. Additionally, SwRI is investigating the use of fracture mechanics and probabilistic design for cylinder heads, utilizing SwRI's NESSUS® software.

Accomplishments - Phase 1 of the program has been completed. A background analysis was conducted that demonstrated existing state-of-the-art heavy duty diesel cylinder heads have a clear limitation on increasing peak firing pressure levels. The design of experiment study has been completed and revealed a number of key relationships, including some complex interactions, between geometric design of the cylinder head and peak firing pressure capability. A number of novel features and combinations of features have also been identified. The remaining critical engine components were ranked on their sensitivity to high cylinder pressure and the availability/feasibility of a solution. Phase 2 of the program has been proposed where SwRI will design a cylinder head for a heavy duty diesel engine capable of withstanding 250 bar cylinder pressure. In addition to the cylinder head design, SwRI has proposed analysis of the cylinder block and head gasket joint to further investigate the ability of these components to cope with cylinder pressures of 250 bar.

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