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It has been proposed that downspeeding combined with high boost levels would effectively reduce fuel consumption in heavy-duty diesel engines. Under low-speed and high-boost operating conditions, however, the in-cylinder gas pressure, which acts on the piston crown, is greater than the piston inertia force (such that there is no force reversal), over the entire range of crank angles. Therefore, the piston pin never lifts away from the main loading area (the bottom) of the connecting rod small-end bushing where the contact pressure against the piston pin is highest. In such operating conditions, lubricant starvation is easily induced at the interface between the piston pin and small-end bushing. Through carefully devised engine tests, the authors confirmed that the piston pin scuffing phenomenon arises when the boost pressure exceeds a critical value at which the no-force reversal condition appears.

The application of high-efficiency diesel engines, hybrid systems, waste heat recovery (WHR) systems, aftertreatment systems, and advanced drivetrains were all examined as possible approaches to improve the fuel consumption of heavy-duty, long-haul commercial trucks that mainly drive on highways. In this study, the strategies that were employed in an effort to improve the fuel consumption performance of the diesel engine itself and the results of evaluating and testing the actual engine are reported.