Studies on Mechanism of Lubricating Oil Consumption for Diesel Engines Lubricated with Low Viscosity Oils

Abstract

Tribotechnology has been required in internal combustion engines to improve fuel economy, limit the impact of global warming, and to conserve resources. In diesel engines, the emission of sulfide ash, phosphorous and sulfur contents from consumed engine oil degrades the exhaust gas after-treatment devices. Low-tension piston rings and/or low-viscosity oils are being increasingly employed to reduce frictional power losses. Work on controlling the lubricating oil consumption (LOC) in such engines was presented at the 2016 CIMAC Congress .

One of the major factors influencing LOC is the oil transported to the combustion chamber by the ring-pack. The amount of lubricant remaining on the cylinder wall above the piston will influence the LOC through evaporation and burning of the oil. Thus an understanding of the film thickness under the top ring is of vital importance and this, in turn, is influenced by the behaviour of the full ring-pack, the lubricant’s properties, the geometry and surface finish of the cylinder, piston dynamics and engine conditions.

Many researchers have modelled and/ or measured ring-pack film thicknesses and a wide variation in these values has been observed. In the ring pack, the oil-film thicknesses under the compression rings are influenced by the amount of oil left behind by the oil control ring on the down-stroke, with the film thickness on the up-stroke being affected by the amount of oil left by the top compression ring.
Lubricating oil evaporation, LOE, from the film on the cylinder wall depends on the physical properties of the oil and the operating condition of engine [reference]. An analytical model of evaporation for multi-species component oils has been developed to study influencing factors of LOE. Factors such as the operating condition (with or without supercharging), the gas pressure in the combustion chamber, the rotational speed, the temperature of cylinder wall surface, the oil-film thickness formed by piston rings under the mixed lubrication in the ring pack and the viscosity & volatility of the oil have been considered
This paper will present results from three studies: (1) the experimental verification of a previously-published analytical model for Lubricant oil evaporation (LOE); (2) measurements of the changes of viscosity and volatility characteristics of the new multi-species, super-low viscosity oils (including synthetic oils); and (3) measurements of film thickness under the oil control ring of a 4-stroke engine.