A review of emission products from bioethanol and its blends with gasoline. Background for new guidelines for emission control
Bioethanol–gasoline blends represent an emerging direction in the attempts to reduce GHG emissions, urban and road-side pollution and to limit the use of fossil fuels in vehicle engines. As a result of the biofuel directives, an increasing number of vehicles is gradually adapting bioethanol–gasoline blends, and concerns are arising in context with their new and poorly studied emission profiles. Compared to conventional ethanol–gasoline blends, the introduction of bioethanol can add new parameters to the emission profiles of the sharply increasing number of vehicles worldwide. This review sheds light on the known and anticipated emission products from combustion of blends of gasoline and bioethanol, their toxic properties and the expected role of additive chemistry on pollution profiles.
The results presented herein show that benzaldehyde, acetaldehyde, formaldehyde and VOCs are the dominant emission products from bioethanol similarly to ethanol–gasoline blends. However, the presence of additives, such as ETBE and MTBE adds further complexity to expected emission profiles, followed by proprietary additives, lubricants and detergents which – based on a limited amount of available information, show that further research is required. Our conclusions suggest that a generic reduction of amine-based additives in blends is a safe approach for reducing toxicity of bioethanol–gasoline blends. Oxygenated additives however, are expected to have a reduced toxicity from the emissions compared to amine-based types, nevertheless, studies show that also these, based on their concentrations can introduce considerable risks to the health and the environment. The implementation of novel catalyst technologies applied on bioethanol–gasoline blends may therefore be an avenue of reduction of the toxic components deriving from bioethanol–gasoline blends.