Effects of ethanol-blended gasoline on air pollutant emissions from motorcycle

The effect of ethanol–gasoline blends on criteria air pollutant emissions was investigated in a four-stroke motorcycle. The ethanol was blended with unleaded gasoline in four percentages (3, 10, 15, and 20% v/v) and controlled at a constant research octane number, RON (95), to accurately represent commercial gasoline. CO, THC, and NOx emissions were evaluated using the Economic Commission for Europe cycle on the chassis dynamometers. The results of the ethanol–gasoline blends were compared to those of commercial unleaded gasoline with methyl tert-butyl ether as the oxygenated additive. In general, the exhaust CO and NOx emissions decreased with increasing oxygen content in fuels. In contrast, ethanol added in the gasoline did not reduce the THC emissions for a constant RON gasoline. The 15% ethanol blend had the highest emission reductions relative to the reference fuel. The high ethanol–gasoline blend ratio (20%) resulted in a less emission reduction than those of low ratio blends (< 15%). This may be attributed to the changes in the combustion conditions in the carburetor engine with 20% ethanol addition. Furthermore, the influence of ethanol–gasoline blends on the reduction of exhaust emissions was observed at different driving modes, especially at 15 km/h cruising speed for CO and THC and acceleration stages for NOx.