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This experimental work investigates the possibility of reducing the lubricating oil impact on diesel exhaust emissions, particularly concerning the particulate matter, by means of a three-stage experimentation on a Hydra Diesel research engine. The influence of the physical characteristics of the oil was evaluated in the first stage. The results showed that the use of low viscosity oils leads to a better mechanical efficiency and a lower specific fuel consumption than high viscosity oils in the examined viscosity range. Emission tests at a high constant load showed a higher Air Fuel Ratio (AFR) for low viscosity oils compared to high viscosity ones, due to a lesser fuel consumption. As CO, Particulate emissions and smoke are greatly affected by AFR at high load, a decrease of these emissions occurs moving towards low viscosity oils. The influence of the chemical characteristics of the oil was evaluated in the second stage.

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).