Ford researchers suggest using higher ethanol blends to boost the minimum octane number of regular-grade gasoline
Using higher volume blends of ethanol to leverage the alcohol’s inherent high octane rating to produce ethanol-gasoline blends with higher octane numbers could yield “substantial societal benefits”, according to a team of researchers from Ford Motor Company.
Currently, ethanol is blended into a gasoline blendstock formulated with lower octane rating such that the net octane rating of the resulting final blend is unchanged from historical levels. However, the high octane rating of ethanol could be used in a mid-level ethanol blend to increase the minimum octane number (Research Octane Number, RON) of regular-grade gasoline, J.E. Anderson and colleagues suggest in a new paper published in the journal Fuel.
Ethanol—and methanol—have some performance issues in gasoline blends, such as lower energy density than gasoline, potentially higher or lower vapor pressures, altered distillation properties, and potential for water-induced phase separation. However, they also offer a high research octane number (RON) and motor octane number (MON) as compared to gasoline. The alcohols also have a greater latent heat of vaporization than gasoline, which contributes to their higher RON values and provides additional charge cooling in direct-injection (DI) engines.
The octane number reflects the ability of a fuel to resist “knock”—resulting from premature autoignition—in spark-ignited engines, which can cause engine damage when severe.
Higher RON in the fuel blend would enable greater thermal efficiency in future engines through higher compression ratio (CR) and/or more aggressive turbocharging and downsizing, and in current engines on the road today through more aggressive spark timing under some driving conditions.
Using a linear molar octane blending model they had developed earlier to quantify RON potential from ethanol and blendstock, the team estimated that an increase of 4-7 points in RON are possible by blending in an additional 10–20%v ethanol above the 10% already present. Keeping the blendstock RON at 88 (which provides E10 with ∼92.5 RON), they estimated RON would be increased to 94.3 for E15 to as much as 98.6 for E30. Further RON increases may be achievable assuming changes to the blendstock RON and/or hydrocarbon composition, they suggested.
An increase in blendstock RON from 88 to 92 would increase the RON of E10 from 92.5 to 95.6, and would provide higher RON with additional ethanol content (e.g., RON of 97.1 for E15 to 100.6 for E30).
Under scenarios considered in the paper, the team estimated CR increases to be on the order of 1–3 CR-units for port fuel injection engines as well as for direct injection engines in which the greater evaporative cooling of ethanol can be fully utilized.
J.E. Anderson, D.M. DiCicco, J.M. Ginder, U. Kramer, T.G. Leone, H.E. Raney-Pablo, T.J. Wallington (2012) High octane number ethanol–gasoline blends: Quantifying the potential benefits in the United States, Fuel doi: 10.1016/j.fuel.2012.03.017
J. E. Anderson, U. Kramer, S. A. Mueller, and T. J. Wallington (2010) Octane Numbers of Ethanol− and Methanol−Gasoline Blends Estimated from Molar Concentrations, Energy & Fuels 2010 24 (12), 6576-6585 doi: 10.1021/ef101125c