Effect of ethanol–gasoline blends on CO and HC emissions in last generation SI engines within the cold-start transient: An experimental investigation

Highlights: • This study assesses the effect of ethanol–gasoline blends on cold emissions. • A last generation motorcycle was operated on the chassis dynamometer. • A new calculation procedure was applied to model the cold transient behaviour. • The 20% v/v ethanol blend shows the highest reduction of CO and HC cold emissions. - Abstract: Urban areas in developed countries are characterized by an increasing decline in air quality state mainly due to the exhaust emissions from vehicles. Besides, due to catalyst improvements and electronic mixture control of last generation engines, nowadays CO and HC cold start extra-emissions are heavily higher than emissions exhausted in hot conditions, with a clear consequence on air quality of the urban contexts. Ethanol combined with gasoline can be widely used as an alternative fuel due to the benefit of its high octane number and its self-sustaining characteristics. Ethanol, in fact, is well known as potential alcohol alternative fuel for SI engines, since it can be blended with gasoline to increase oxygen content, then decreasing CO and HC emissions and the depletion of fossil fuels. Literature data about cold emissive behaviour of SI engines powered with ethanol/gasoline blended fuels are rather limited. For this reason, the aim of this study is to experimentally investigate the effect of ethanol/gasoline blends on CO and HC cold start emissions of four-stroke SI engines: a last generation motorcycle was operated on the chassis dynamometer for exhaust emission measurements without change to the engine design, while the ethanol was mixed with unleaded gasoline in different percentages (10, 20 and 30 vol.%). Results of the experimental tests and the application of a new calculation procedure, designed and optimised to model the cold transient behaviour of SI engines using different ethanol–gasoline blends, indicate that CO and HC cold start emissions decrease compared to the use of commercial gasoline, with the 20% v/v ethanol blend achieving the highest emission reduction. Moreover, in this paper a review of the recent scientific literatures was performed on the emissive behaviour of SI engines fuelled with ethanol–gasoline blended fuels.