The present work, carried out within the framework of the JOULE-3 European joint project entitled “Fuel and lubricant formulations for high de-polluted engines”, investigates the effect of both the fuel and the lubricating oil quality on deposits, wear and exhaust emissions in the presence of a high EGR rate, with specific attention to the emission variation during aging.
Two fuels (a current Italian typical fuel and a Swedish high quality fuel) and two lubricants (a traditional mineral oil SAE 15W-40/ACEA B2 and a full synthetic SAE 0W-40/ACEA B3) were used to carry out six tests, each one characterized by 126-hour duration at different running conditions, on a VM Turbotronic Diesel engine.
The engine evaluation pointed out an interaction between oil and fuel: if the high quality fuel (nearly zero S) is used, a low level of cylinder bore polishing and top ring wear, weakly affected by the oil quality, occurs. When changing to the use of the current fuel (about 0.05% S), a large increase of polishing and wear occurs with the mineral oil, while the full synthetic and lower viscosity oil assures a moderate increase of wear. The analysis of piston deposits and sludge confirmed the worse behavior of the current fuel in comparison with the high quality fuel.
The analysis of the soot content in the used oils showed that the current fuel leads to a contamination three times higher than the high quality fuel. All the tests were characterized by a similar increasing trend of Total Acid Number, which demonstrates a low influence of fuel sulfur content on oil acidity.
The combination of the mineral oil and the current fuel caused the highest emission of particulate that can be reduced only by changing to the use of the high quality fuel and/or the synthetic oil.
An increasing trend of particulate emissions, NOx and CO2, as a function of running time, emerged in particular when the current fuel is used. An oil change at the end of 126-hour durability test led the emissions close to the initial level, which demonstrates that the increasing trend of emissions is more due to the oil aging than to the engine aging.