Development of high performance diesel piston using bowl edge re-melting technology

Abstract

Significant efforts have been devoted to developing diesel engine technologies to meet the stringent emission legislation. From the combustion point of view, combustion pressure is getting higher with higher injection pressure and boosting pressure, which enhance the combustion process and thus reduce the emissions. This issue requires reinforcement of the piston as well as improvement of cooling performance in the piston. The objective of this study was to develop a high performance diesel piston using bowl edge re-melting technology. The weakest point in the piston is the bowl edge where the fuel jet impingement and combustion flame exposure are concentrated. The bowl edge after piston casting process was re-melted by the tungsten inert gas (TIG) welding. The bowl edge was then strengthened due to rapid local solidification, leading to finer grain of the material. Furthermore, the shape of cooling gallery in the piston was re-designed and the location of cooling gallery was changed to investigate their effects on cooling performance. The developed pistons were applied and evaluated in a diesel engine for a passenger vehicle. It was confirmed that the shape and location of cooling gallery played an important role in determining the piston temperature. In the durability test, which was done at full load condition during 100 hours, a visual inspection after the test revealed no problems with the piston.