I finally Googled around about specific gravity levels of various fuels and stumbled on THIS gem (it gets a bit involved, but sums up a lot of what has been said about ethanol) ----
The myth of ethanol as a fuel
With the price of petrol on the rise it was only a matter of time before the same old people would drag the same old products out of the closet and tout them as the all new, green, clean fuel solution to rising fuel prices and saving the environment. So it should be no surprise to hear the same old lobby beating the hell out of the ethanol drum. First, let me say that from an economic point of view, with current production technology, ethanol is environmentally wasteful in that it consumes more kilo joules of energy in its production than it then produces in the engine of a motor vehicle.
So why all the fuss? Further, ethanol is not a viable fuel in its own right. To stoichiometrically burn pure ethanol would require an air fuel ratio of 9.0:1 and produce extremely harmful exhaust emissions. It is primarily used as a fuel extender to reduce the consumption of pure petrol. So, what is ethanol? Ethanol (C2H5OH) is a monohydric primary alcohol. It melts at -117.30C and boils at 78.50C. It is miscible (i.e., mixes without separation) with water in all proportions and is separated from water only with difficulty. Ethanol that is completely free of water is called absolute ethanol. It has a specific gravity of 0.79 and consists of 52% carbon, 13% hydrogen and 35% oxygen and it is the oxygen contained within the fuel that makes it of so much interest. Unfortunately, ethanol has a comparatively low calorific value* of only 28.6 MJ/kg compared to 43.5 MJ/kg of petrol which means that it requires an additional 35% more ethanol to release the same amount of energy as petrol.
This fact is clearly revealed by comparing the stoichiometric air/fuel requirement of petrol (14.73:1) to that of ethanol (9.0:1). However, this disparity is not born out in test results. In general, the fuel economy of an engine using a 10% ethanol/petrol blend is usually only 3% to 4% lower than the same engine using 100% petrol as a fuel. Ethanol is hygroscopic, which means it readily absorbs moisture from the atmosphere. The use of ethanol in fuel means that water will be absorbed from the atmosphere and passed along with ethanol and fuel to the combustion chamber of the engine. As long as the ethanol is correctly stored prior to blending with raw fuel there should not be any problems. However, when pure ethanol is exposed to the atmosphere for prolonged periods it will absorb unacceptable levels of moisture from the air. All of which means that ethanol should be blended with fuel as soon as practical after final processing. An often overlooked fact about ethanol is the large disparity between its viscosity (stickiness or ability to flow) and that of the petrol, the fuel it is most generally mixed with. At 200C the viscosity of ethanol is 1.5 mm2/s where as petrol is only 0.60 mm2/s.
This can cause fuel flow problems around high flow/small orifice areas such as injector pintles and discharge nozzles that were only designed for the passage and metering of petrol. This additional viscosity can cause driveability emission problems when the vehicle is briskly accelerated from a standing start. Ethanol burns in air with a blue flame forming carbon dioxide and water and reacts with active metals to form the metal ethoxide and hydrogen, e.g., with sodium it forms sodium ethoxide. It reacts with certain acids to form esters, e.g., with acetic acid it forms ethyl acetate. It can be oxidised to form acetic acid and acetaldehyde. It can be dehydrated to form diethyl ether or, at higher temperatures, ethylene. I will discuss this fact further in my next article.
Preparation Ethanol is the alcohol of beer, wines, and liquors. It can be prepared by the fermentation of sugar (e.g., from molasses) which requires an enzyme catalyst, that is present in yeast, or it can be prepared by the fermentation of starch (e.g., from corn, rice, rye, or potatoes), which requires, in addition to the yeast enzyme, an enzyme present in an extract of malt. The concentration of ethanol obtained by fermentation is limited to about 10% (20 proof) since at higher concentrations ethanol inhibits the catalytic effect of the yeast enzyme. (The proof concentration of an alcoholic beverage is numerically double the percentage con-centration.) For non-beverage uses, ethanol is more commonly prepared by passing ethylene gas at high pressure into concentrated sulphuric or phosphoric acid to form the corresponding ester. The acid-ester mixture is diluted with water and heated, forming ethanol by hydrolysis, and the alcohol is then removed from the mixture by distillation, usually with steam.
Still in the future Cellulose: There has yet to be a commercial plant using cellulose from agricultural or municipal wastes as a feedstock, instead of the more traditional feed stocks. The ethanol from the cellulose process is complex and costly and is still in the research and development stage. Uses Ethanol is used extensively as a solvent, disinfectant and as a fuel and gasoline extender called gasohol. Many U.S. automobiles manufactured since 1998 have been specially equipped as duel fuel vehicles to enable them to run on either gasoline or E85, a mixture of 85% ethanol and 15% gasoline. However, E85 is not yet widely available which implies that engines do have to be specially engineered, in both metallurgy and engine management, to run successfully on ethanol both for engine longevity and to meet emission standards. Engineers have been tinkering with the idea of using ethanol as a fuel for a very long time and its something of mystery why the current crop of ethanol proponents would spend so little time researching previous experiences, particularly the issue of economically viable production.
It is interesting to scan the time line (right) to see exactly when ethanol came into use. At no stage in 180 years has any company, organisation or individual, managed to economically produce ethanol for use as an automobile fuel. It has always required the intervention of governments to prop up ethanol production with a subsidy. The operative word in the history of enthanol appears to be subsidy. Apart from needy special interest groups such as cane farmers and a politically well-connected manufacturer, no one benefits. So it is hard to under-stand why Australia is going down this road especially when we enormous reserves of LPG which really could do the job. The decision to blend petrol and ethanol is more about the realities of politics than engineering. So whats new? In my next article, I will discuss the effects of ethanol on engine performance, fuel economy, engine metallurgy, engine management and exhaust emissions. * Calorific value is the calories, or thermal units, contained in one unit of a substance and released-heat release-when the substance is burned.
