The major engine operation issues with alcohol-blended fuels are fuel quality, volatility, octane number, enleanment, cold start, hot operation, and fuel con­sumption. The physical properties of the blended fuels compared to pure gasoline are shown in Table 7.3. Octane numbers determined by the usual ASTM proce­dures indicate that alcohol-blended gasoline increases fuel octane over the base

Source: Guerrieri, D. A., Caffrey, P. J. and Rao, V, Investigation into the Vehicle Exhaust Emissions of High Percentage Ethanol Blends, SAE Technical Paper Series, #950777, 1995.

gasoline (23-28). Fuel consumption increases when oxygenates are blended with gasoline due to the lower energy content of the oxygenated fuel. Table 7.4 shows that fuel economy decreases with ethanol concentration. The theoretical increase in fuel consuption is 3% for E10 and 6% for E20 (29).

Corrosion of metallic fuel system components is generally not an issue with E10 (28). Researchers have also shown that E20 blends do not appear to affect fuel-system operation (8). Elastomeric and plastic components of new engines are compatible with E10, but many older engines are not (28). Evidence reported has shown that ethanol blends offer less lubrication than pure gasoline (29);

however, that has not been a noticeable issue in terms of wear or engine life over the last 20 years. Over the last few years, Brazil has shown that conventional catalysts used in U. S. vehicles can operate on 10% and neat (100% ethanol) (30). Ref. 8 states that higher ethanol blends show higher catalytic efficiency, because there is a smaller concentration of sulfur species. Barnes (1999), from Ref. 8, says that the increase in catalytic efficiency could be as large as 24%. Guerrieri, Caffrey, and Rao 1995 from Ref. 8 show that volatility decreases with higher ethanol blends. The highest volatility is around 5% ethanol (31). Carbon mon­oxide emissions are lower for ethanol blends (32-35). E10 can be employed in vehicles without equipment changes and without violating manufacturer’s war­ranties (4).

Enleanment is defined as an excess of oxygen compared to the ideal air/fuel ratio. Common problems of enleanment are loss of power and engine misfires (8). Both problems increase emissions. Finland has shown that E15 vehicles can operate with stock carburetors and that 80% of vehicles running on E15 show less wear compared to pure gasoline. Fluorinated polymers have good resistance to both gasoline and ethanol (36). Nylon-coated nitrile rubber has also shown resistance to both gasoline and ethanol (37). Overall, engine operation and life (wear) are not affected by small (10-20%) concentration of ethanol blended with unleaded gasoline.