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Some heavier alcohols than ethanol have been considered as gasoline components, particularly bio-based isobutanol and n-butanol. In the past, “gasoline-grade” tert-butanol (GTBA) was commonly present in gasoline as a co-solvent for methanol and denaturant for ethanol. Properties of butanol are closer to gasoline than properties of ethanol; e.g. heating value, blending vapor pressure, water tolerance, corrosivity and polarity. Octane numbers of isobutanol and n-butanol are lower than those of ethanol. Blending ratio of butanol is higher than that of ethanol within the same oxygen limit, e.g. 3.6 wt-% oxygen is equivalent to 15-16 vol-% of butanol, but 10 vol-% of ethanol. Compatibility of isobutanol and n-butanol with conventional cars and infrastructure is better than that of ethanol. Butanol is not very aggressive towards materials and phase separation risk is low. There are limited emission studies concerning butanol as fuel, especially as concerns cars equipped with three-way catalyst. These tests have shown an increase in in volumetric fuel consumption when n-butanol was added into gasoline. CO, HC and NOx emissions did not change significantly when n-butanol blend was compared to gasoline. Lower PM emission has been reported for butanol than for non-oxygenated gasoline with the direct injection car. Formaldehyde, acrolein, butyraldehyde, methacrolein, and some other unregulated emissions seem to increase with butanol containing fuels when compared to non-oxygenated gasoline.


Compatibility and emissions


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