GEM Ternary Blends: Removing the Biomass Limit by using Iso-Stoichiometric Mixtures of Gasoline, Ethanol and Methanol 2011-24-0113

The paper presents the concept of ternary blends of gasoline, ethanol and methanol in which the stoichiometric air-fuel ratio (AFR) is controlled to be 9.7:1, the same as that of conventional ‘E85’ alcohol-based fuel. This makes them iso-stoichiometric. Such blends are termed ‘GEM’ after the first initial of the three components. Calculated data is presented showing how the volumetric energy density relationship between the three components in these blends changes as the stoichiometric AFR is held constant but ethanol content is varied. From this data it is contended that such GEM blends can be ‘drop-in’ alternatives to E85, because when an engine is operated on any of these blends the pulse widths of the fuel injectors would not change significantly, and so there will be no impact on the on-board diagnostics from the use of such blends in existing E85/gasoline flex-fuel vehicles. The resulting ability of such blends to extend the reach of a fixed amount of ethanol in the fuel pool is then demonstrated, together with the mechanism by which the addition of the methanol displaces additional gasoline. If the methanol used is of a renewable and energy-secure nature then, for a fixed volume of ethanol in the fuel pool, an increased level of renewability and energy security is achieved. This overall situation is made possible by the fact that there are more E85/flex-fuel vehicles in existence than can currently be serviced by the E85 fuel supply chain. Example price calculations are conducted to show the points of potential price competitiveness.

Preliminary tests with such GEM blends in a production-specification E85/gasoline vehicle were conducted to show the validity of the approach, and the results are reported together with fuel characteristics such as RON, MON and sensitivity. Road mileage is also reported using one of the fuel blends. Together these findings show the attractiveness of the concept and that there is therefore a possibility to significantly extend the use of renewable alcohol fuel in the market due to the miscibility of gasoline, ethanol and methanol. This is primarily because, when they are blended to a target stoichiometric AFR, any of the blends possible share essentially the same volumetric energy content, RON, MON, sensitivity and latent heat (to within 4%). In turn, this makes taxation and pricing of such fuels simple and straightforward, further removing roadblocks to introduction.