For each country, there is a limit beyond which sustainable ethanol cannot be made from biological feedstocks. This fact has been used by some on occasion to rule alcohols out as viable long-term energy carrier for transport.
This is unfortunate, because in most respects, the low-carbon-number alcohols (which include ethanol) offer a very attractive alternative to a transport energy economy based on electricity or molecular hydrogen, both of which will entail significant extra cost being absorbed by the consumer in the long term because they require radically different vehicles, distribution infrastructure, or both.
Transition to an energy economy based on alcohols would be an evolutionary process and not a revolutionary one. This is because, unlike the alternatives, the alcohols are miscible with gasoline, which alleviates the supply infrastructure and vehicle storage issues. While a small on-cost is incurred with adoption of alcohol/gasoline flex-fuel technology, this is likely to be in the region of only $100-200 per vehicle, and not in the $10,000 per vehicle region which a 100 mile range traction battery or molecular hydrogen storage system would cost. As such, flex-fuelling is attractive except for supply of fuel to the marketplace.
Lotus has been conducting tests on a fuel blending concept intended to circumvent the biomass limit of ethanol by co-blending it with both methanol and gasoline. Briefly, for any binary gasoline-ethanol mixture (such as E85), a ternary blend of gasoline, ethanol and methanol can be substituted in which the volume fraction of each individual component is chosen to yield the same stoichiometric, or chemically-correct, air-fuel ratio (AFR). For E85 this AFR is 9.7:1, and a family of equivalent, or ‘iso-stoichiometric’, ternary blend fuels can be created ranging from E85 to M56 (see Figure 1).
In order to describe the volumetric proportions more accurately, these two limit blends would be termed G15 E85 M0 and G44 E0 M56, and the family of blends is generally described as GEM blends.
Importantly, all of the iso-stoichiometric blends have been found to have essentially identical volumetric energy content (based on the masses and densities of the individual components). This suggests the possibility that drop-in blends equivalent to E85 can be created which could distribute the available ethanol across a greater total volume of fuel supplied. Since gasoline is displaced, a more beneficial situation is arrived at if the methanol used is better from a carbon intensity or energy security viewpoint.
At the same time, based on the mass proportions of the individual components, the latent heat of the blends was calculated and found to vary by 2%. Thus the essential prerequisites to produce truly drop-in fuels are satisfied.
Vehicle tests were then conducted using a production flex-fuel vehicle supplied by Saab Automobile Powertrain AB. A procedure was drawn up in order to change the test fuel and condition the vehicle identically for each blend, and then to operate it on one cold and two hot New European Drive Cycle (NEDC) tests.
Results, in terms of tailpipe CO2 and vehicle energy utilization, are shown in Figures 3 and 4, respectively.
Note that, in general, the alcohol blends have better energy utilization than gasoline: this is of the order of ~ -5% when the vehicle is hot, with important ramifications for wellt to-wheel efficiency in a renewable energy economy.
During testing in the emissions lab two malfunction indicator lights (MILs) were illuminated, but only when binary gasoline-methanol blends were tested, i.e. G44 E0 M56. No such lights occurred when ethanol was present in the blends. This underlines that a co-solvent is necessary when gasoline and methanol are blended together. Ethanol is known to be an excellent co-solvent for these two components. Note that other co-solvents for methanol and gasoline exist, and the question of which and how much co-solvent is necessary is one that requires further work.
When the emissions laboratory test work had been completed, the vehicle was fully fuelled with Blend C and the car driven on a road trip from Norwich to Trollhätten. This first tankful of fuel was used for 425 km with an average fuel consumption 11.88 litres per 100 km (23.75 mpg Imperial, 19.78 mpg US). There was no MIL activity during this trip and eight cold starts were performed, including one at -4°C, with no perceptible difference in starting to subsequent tanks of gasoline.
As a consequence of this work it is believed that such ternary blends have the potential to become drop-in alternatives to equivalent-stoichiometry ethanol-gasoline blends. Further work is warranted to prove this claim. Immediately, this means testing a car with a physical alcohol sensor, a difference to the car employed, which utilized an indirect approach for initial AFR control based on the fuel tank level sensing system. This is often referred to as a virtual sensor.
It is possible to show that GEM ternary blends with a high proportion of methanol can be cheaper than gasoline on a cost per unit energy basis. This is because methanol is much cheaper than gasoline (and ethanol) on a volumetric basis. Using wholesale prices of $3.00/US gallon gasoline, $2.30 for ethanol and $1.30 for methanol, Blend C is slightly cheaper than gasoline per unit energy. This does not include the ~ 5% improvement in energy utilization for the blend, which would translate into a similar reduction in operating costs for the consumer.
While this calculation uses a price for methanol based on its manufacture from fossil feed stock, and assumes that taxation would be on a per unit energy basis, the result does underline the fact that since methanol is cheap to produce it allows a situation where an affordable alternative fuel technology could actually be preferable financially for the customer without government subsidy. Neither electrification nor a molecular hydrogen economy permits this.
Furthermore, once large volumes of methanol are being used for transportation, there then exists an evolutionary route to effective decarbonisation through the ease by which it can be made from waste or CO2 which could be extracted from the atmosphere to solve fully the issue of greenhouse gas emission and energy security [3-17].
It is intended to revisit the economics of ternary blends and report on some initial materials compatibility tests in a later article, but in conclusion here it seems that they could permit evolution to a carbon-free end game where vehicles remain affordable and the taxation system is stable.
The process can begin immediately if the necessary vehicle durability testing of the ternary blends is satisfactory. Furthermore, the needs of all stakeholders in transportation are satisfied:
Governments: because there will be a lower immediate investment in renewable energy and there is no requirement for immediate government subsidies.
Fuel companies: (a) because the production of renewable methanol from recycled CO2 will ultimately free manufacturers from their reliance on fossil-derived feed stocks sourced from geopolitically sensitive regions or geophysically challenging environments; (b) because there will be no step-change required from a liquid fuel infrastructure to an alternative which will entail greater expense.
Vehicle manufacturers: who are struggling to make profit anyway, and for whom this approach ensures that they will not have to write off existing and expensive production lines.
Vehicle customers: who will still be able to purchase affordable vehicles and fuel.
When renewable methanol is used, it is believed that no long-term alternative strategy presents such an attractive combination of attributes. Instead of being ruled out essentially due to the limited supply of ethanol, the alcohols are ruled in as a potential incumbent energy carrier for transportation.
Authors: Richard Pearson and Jamie Turner
An initial test programme has been conducted to investigate these GEM blends and is reported in detail in a recent SAE paper . This article will report some of the results. In order to perform this test, a control gasoline was quarantined, and four blends specified, blended and tested. These blends were:
- Blend A – G15 E85 M0 A test fuel representing a nominal ‘E85’ blend.
- Blend B – G29.5 E42.5 M28 This test fuel splits the available ethanol across twice the total volume of fuel.
- Blend C – G37 E21 M42 In a manner similar to Blend B, this blend splits the available ethanol across four times the total volume of fuel. Additionally, methanol is twice the volume of ethanol, and the total volume of alcohol is approximately twice that of gasoline
- Blend D – G44 E0 M56 This is the extreme of range of ternary blends at 9.7:1 stoichiometric AFR, and is the binary methanol-gasoline equivalent of the nominal E85.
After accurate blending, the fuels were and analyzed for various properties including octane number, which is shown in Figure 2. Immediately apparent is that the octane numbers are constant across the entire family of GEM blends; this fortuitous linear blending relationship for alcohols in ‘gasoline’ has only recently been shown by others .
Lotus Engineering would like to acknowledge the help and assistance of the partners in the project, including BioMCN, Saab Automobile Powertrain AB and Inspectorate.
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