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Low and ultra low viscosity oils are one of the main solutions considered in view of the improvement of energy efficiency for better fuel economy. The recent modification of SAE J300 engine oil viscosity classification, to include engine oils with high temperature & high shear rate (HTHS) viscosity of 2.3 mPa·s for the SAE 16 grade, has opened debate on the possible real benefits that could derive, in terms of fuel economy and CO2 emission reduction, from the use of ultra low viscosity oils on engines of current technology. Two European compact cars (C-segment) of recent technology and similar characteristics were employed in our laboratories, on chassis-dyno test bed, to evaluate fuel economy with the use of oils having an HTHS viscosity decreasing from 2.9 to 2.0 mPa·s, with a −0.3 mPa·s step.

Great efforts have been paid to improve engine efficiency as well as to reduce the pollutant emissions. The direct injection allows to improve the engine efficiency; on the other hand, the GDI combustion produces larger particle emissions. The properties of fuels play an important role both on engine performance and pollutant emissions. In particular, great attention was paid to the octane number. Oxygenated compounds allow increasing gasoline's octane number and play an important role in PM emission reduction. In this study was analyzed the effect of fuels with different RON and with ethanol and ethers content. The analysis was performed on a small GDI engine. Two operating conditions, representative of the typical EUDC cycle, were investigated. Both the engine performance and the exhaust emissions were evaluated. The gaseous emissions and particle concentration were measured at the exhaust by means of conventional instruments.