Effect of ethanol blends on soot formation and emissions in a GDI optical engine

Gasoline direct injection (GDI) systems were introduced to improve fuel economy and decrease the emissions of greenhouse gases. On the other hand, GDI engines are negatively characterized by large emissions of particulate matter (PM) emissions. The use of oxygenated fuels, such as ethanol, can help in reducing particulate emissions, thus allowing facing the challenges to meet future emissions standards. This study explores the influence of ethanol on particulate matter formation and emissions in GDI engines. Experimental investigation was carried out in an optical 4-stroke cylinder engine. The engine displacement was 250 cm3. It was equipped with an elongated piston with a wide sapphire window in the head and a quartz cylinder liner. The engine was fuelled with neat gasoline and ethanol, and ethanol/gasoline blends at 20% v/v, 50% v/v and 85% v/v. Measurements were carried out at different engine speeds and loads in order to perform a comprehensive study of soot formation in GDI engines. Optical techniques based on 2D-digital imaging were used to follow the combustion process and soot formation. Particle emissions were characterized in terms of number concentrations and size distribution using a differential mobility particle sizer.