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Alternative Fuels for Motor Vehicles
Ethanol
Ethanol is the alcohol we all consume in beers, wines and spirits that is produced by the fermentation of the sugar found in natural products such as grapes and grain.
Ethanol for fuel purposes is made in the same way; by fermentation of sugar produced from grain crops. Ethanol can also be made from cellulose biomass such as trees and grasses - more usually called bioethanol in this case.
Ethanol is normally used as an additive to gasoline (petrol) and can be mixed with petrol at up to 15% inclusion and used in cars running on ordinary unleaded petrol. Bioethanol is already mixed with petrol in the UK by Tesco and sold at a number of filling stations in the South-East of England.
But once again the main mover in the market is the USA, with their huge grain producing capacity. Ethanol can be produced from corn, barley, and wheat, but also from cellulose such as corn stalks, rice straw, sugar cane pulpwood, grass, and municipal solid waste. Because of the variety of feed stocks that can be used, ethanol offers tremendous opportunities for new jobs and economic growth outside the traditional "grain belt." In other words there is a political dimension to these developments. One of the main driving forces in the USA is the limited crude oil supplies and refining capacity, and rising concern over environmental degradation. There is major political concern about the possibility of the country being reliant upon imported crude oil that is driving this policy.
Ethanol is not as energy rich as Petrol so more is needed to do the same work as the same volume of Petrol. It is actually of a higher Octane rating than Petrol but isn't as volatile. Hence the engine will not actually start on colder mornings. All of which explains why Ethanol is used as a blend additive at around 15%. This is called E85 Fuel.
What all this means is that potentially the performance of Ethanol blend fuel is higher than that of gasoline because E85's high octane rating allows a much higher compression ratio, which translates into higher thermodynamic efficiency. However, Flexible Fuel Vehicles, which are capable of running on both fuels, cannot really take advantage of this octane boost since they also need to be able to run on pump-grade gasoline.
To put a couple of figures into context:
- One acre of corn can produce 300 US gallons of ethanol per growing season.
- The USA uses 200billion gallons of gasoline and diesel per year.
- That amount of Fuel would require 675million acres of grain planted or around 70% of the total farmland.
Hence the choice is to import oil or import food.
There is a side issue here in that burning ethanol as a fuel is carbon neutral because the CO2 generated was originally absorbed by the growing grain and merely being re-released into the atmosphere.
But, and it is a big BUT, the energy to convert the grain to Ethanol is very large, additionally growing corn is an intensive process that requires pesticides, fertilizer, heavy equipment and transport.
The financial jury is still out on this exercise.
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