Investigation of lubrication and tribological behaviors in a diesel engine with the new designed flow-guided combustion chamber

Abstract

Changes to the piston bowl geometry directly affect engine performance, exhaust emissions, combustion characteristics and air/fuel mixture formation. In this study, a new combustion chamber (NCC) geometry for a single cylinder direct injection diesel engine is presented, and experimentally compared with the standard combustion chamber (SCC) geometry. Each combustion chamber was fitted to the engine and performed long-term test for 100 h. The effect of combustion chamber bowl geometry on piston rings and lubricating oil was investigated. Firstly, soot was measured in the engine, and the NCC geometry reduced soot emission by approximately 12.32 % compared to the standard bowl geometry type at part load. With the NCC geometry, homogeneity fresh charge and flame propagation were achieved by providing wall-guided flow. The tribological effect of bowl geometry on the lubricating oil was investigated. In the oil analysis, Al,Ca,Co,Cr,Cu,Fe,Mg,Mn,Mo,Ni and Zn elements were higher in the SCC geometry than in the NCC geometry. Especially at the end of the 100th hour of operation, the presence of elements such as Fe and Al showed an increase in engine wears. The lubricating oil kinematic viscosity for SCC was 111.9 mm2/s at 40 °C and 127.9 mm2/s for NCC. In the new geometry, the flash point temperature of the lubricating oil was measured as 232 °C, while this value in the standard geometry was measured as 222 °C. This showed that the volatility and degree of contamination of the oil was lower with the new geometry. SEM/EDX analysis of the piston rings showed a significant difference between the first and second rings for the two geometries. The wear lines in the standard geometry were found to be deeper and more visible than in the new geometry.