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The physical characteristics of lubricating oils can affect the mechanical efficiency of internal combustion engines and as a consequence the quantity of fuel consumed at constant power output; moreover they can influence the quantity of lubricating oil drawn through pistons and valves towards the combustion chamber. Exhaust emissions can be influenced both by fuel and oil consumption, so the physical characteristics of the oil can indirectly affect them. The purpose of this experimental work is to study the effect of the physical characteristics of lubricating oils on emissions, fuel economy and oil consumption in a light duty diesel engine. The study was carried out on a VM Turbotronic diesel engine characterized by low exhaust emission levels (1996 European limits for passenger car achieved without catalyst) and high specific power (37 kW/litre).

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.