Development of a Structurally Optimized Heavy Duty Diesel Cylinder Head Design Capable of 250 Bar Peak Cylinder Pressure Operation

Historically, heavy-duty diesel (HDD) engine designs have evolved along the path of increased power output, improved fuel efficiency and reduced exhaust gas emissions, driven both by regulatory and market requirements. The various technologies employed to achieve this evolution have resulted in ever-increasing engine operating cylinder pressures, higher than for any other class of internal combustion engine. Traditional HDD engine design architecture limits peak cylinder pressure (PCP) to about 200 bar (2900 psi). HDD PCP had steadily increased from the early 1970's until the mid 2000's, at which point the structural limit was reached using traditional methods and materials. Specific power output reversed its historical trend and fell at this time as a result of technologies employed to satisfy new emissions requirements, most notably exhaust gas recirculation (EGR). While future incremental improvements to specific power are predicted to occur through refinements in existing technology, a significant change in HDD structural architecture is required to allow higher PCP operation. Many proposed combustion, emissions reduction and high efficiency technologies for the future are also pointing to the need for increased PCP. Once higher PCP operation can be achieved, HDD performance can return to its historical trends and enable much of the advanced diesel combustion research ongoing throughout the world today to become more commercially viable. The challenge is to determine what this structural architecture must be.

Southwest Research Institute® (SwRI®) has undertaken an applied research and development program with the goal of evaluating key design features which limit PCP for modern HDD engines and to analytically derive structural solutions that would extend the limit to what is predicted to be required for high specific power model year (MY) 2015 (and beyond) engines. This program focused on identifying combinations of structural parameters and feasible material options in the cylinder head to achieve commercially viable 250 bar PCP capability with minimal impact on existing machining lines. This paper reviews the multi-phase/multi-year program approach and results as well as discusses a new casting method developed for HDD cylinder head manufacture.