Study on Low-Cycle Fatigue Life of Diesel Engine Piston Considering Oil Cooling Gallery Structure

Abstract

Oscillating oil flow in the cooling gallery is one of the most effective cooling methods for highly reinforced diesel engine pistons, and its structure is a key factor affecting the fatigue life of pistons. This study numerically investigates the impact of the oil cooling gallery's cross-sectional shape and position on the low-cycle fatigue life of diesel engine pistons. The piston’s fatigue life was analyzed by the engine bench tests, a fluid-solid coupled heat transfer model and Sehitoglu theory. The results indicate that thermal fatigue damage primarily initiates in the throat region of the piston combustion chamber. This is due to the increased temperature gradient from rapid top surface temperature changes under transition conditions and the crowding effect in the throat area due to the ω combustion chamber structure. As the distance between the oil cooling gallery and the piston's top surface increases, the piston's maximum temperature rises, but the temperature gradient at the top surface gradually decreases. However, the critical stress for plastic deformation of the piston decreases once the throat temperature exceeds a certain threshold, leading to a non-m onotonic trend in the piston's low-cycle fatigue life. The elliptical oil cooling gallery demonstrates a higher heat transfer coefficient, providing superior cooling to the piston's top surface compared to the kidney and teardrop shapes, thus enhancing fatigue life.

Keywords: diesel engine, Piston, Temperature field, Internal cold oil chamber, Low-cycle fatigue