Thursday, July 16, 2009
Anhydrous Ethanol vs. Hydrous Ethanol in Gasoline Blending
By Brian J. Donovan
Renergie
April 22, 2009

Ethanol (C2H5OH), otherwise known as ethyl alcohol, alcohol, or grain spirit, is a clear, colorless, flammable oxygenated hydrocarbon with a boiling point of 78.5 degrees Celsius in the anhydrous state. In transportation, ethanol is used as a vehicle fuel by itself (E100), blended with gasoline (E85), or as a gasoline octane enhancer and oxygenate (10 percent concentration).

Anhydrous ethanol means an ethyl alcohol that has a purity of at least ninety-nine percent, exclusive of added denaturants, that meets all the requirements of the American Society of Testing and Materials (ASTM) D4806, the standard specification for ethanol used as motor fuel.

Hydrous (or wet) ethanol is the most concentrated grade of ethanol that can be produced by simple distillation, without the further dehydration step necessary to produce anhydrous (or dry) ethanol. Hydrous ethanol (also sometimes known as azeotropic ethanol) typically ranges from 186 proof (93% ethanol, 7% water) to 192 proof (96% ethanol, 4% water).

Initial tests conducted in Europe have confirmed that hydrous ethanol can be blended effectively with gasoline without phase separation or other problems. An unmodified Volkswagen Golf 5 FSI was operated successfully on HE15 (15% hydrous ethanol blended with gasoline), meeting European exhaust emission standards in testing conducted by the Netherlands research organization TNO Automotive and by SGS Drive Technology Center of Austria. In addition to confirming the effectiveness of hydrous ethanol for gasoline blending in actual vehicle trials, these initial tests have shown measurable increases in volumetric fuel economy, indicating higher thermodynamic efficiencies resulting from hydrous ethanol. This recently discovered phenomena for mid-level ethanol blends appears to be due to the benefits of oxygenation and heat of vaporization in conjunction with capitalizing on the change in chemical and physical properties which occur as a result of combining water, ethanol, and gasoline. When appropriately combined in mid-level ethanol blends, the chemical reactions of these compounds optimize the efficiency at which internal combustion engines operate. For hydrous ethanol blends, this is accomplished primarily through the total heat of vaporization resulting from combining ethanol and water. Essentially, the lower energy content of hydrous ethanol is counteracted by increasing engine performance due to higher heat of vaporization of ethanol and water in comparison with gasoline and anhydrous blends.

Hydrous ethanol blends (oxygenated hydrocarbons) lower engine operating temperatures due to cooling of intake fuel mixture with 3-6% more water and increasing heat of vaporization when compared to anhydrous ethanol. The result is more efficient combustion, cooler running engines, lower exhaust temperatures, and increased longevity of engine life. The water contained in hydrous ethanol blends also reduces NOx emissions. In addition to the effects of higher water content in hydrous ethanol, ethanol increases compression ratios and decreases engine knocking (detonation). Essentially, both water and ethanol increase the octane level of the fuel mixture. The octane number is a measure of the resistance of a fuel to auto-ignition. It is also defined as a measure of anti-knock performance of a gasoline or gasoline component such as hydrous ethanol. Higher octane levels contribute to enhancing the thermodynamic efficiency of combustion engines, which subsequently increases fuel efficiency. The increase in total engine efficiency results in optimizing fuel efficiency for both ethanol and gasoline.

In addition to the strong hydrogen bonds contained in water molecules, the polarity of the OH groups contained in ethanol molecules can form hydrogen bridges causing relatively strong attractive forces between molecules in liquid phases. Upon vaporization of hydrous ethanol as a fuel, the distance between the water and ethanol molecules increase such that molecular interactions including physical properties are disrupted. This process accumulates a certain amount of latent (stored) energy. During combustion of these vapors, this explains why the heat of vaporization of hydrous ethanol blends is so much higher than that of regular gasoline components and non-alcohol oxygenates like methyl tertiary butyl ether (MTBE) which do not contain OH groups (non-alcohols). High heat of vaporization values are typical for water and alcohols including hydrous ethanol and hydrous ethanol blends (oxygenated hydrocarbons).

According to Baylor University, “as far as safety and performance is concerned, hydrous ethanol is a slightly better fuel [than anhydrous ethanol] in every respect (except specific fuel consumption since water does not provide any caloric content). Small quantities of water absorbed in the fuel result in a slight increase in power caused by the higher latent heat of vaporization of the fuel.”

Previous assumptions held that ethanol’s lower energy content directly correlates with lower fuel economy for automobiles. Those assumptions were found to be incorrect. Instead, the new research strongly suggests that there is an “optimal blend level” of ethanol and gasoline – most likely E20 or E30 – at which cars will get better mileage than predicted based strictly on the fuel’s per-gallon Btu content. The 2007 flex-fuel Chevrolet Impala utilized in midlevel blends testing revealed a 15% increase in fuel efficiency using the Highway Fuel Economy Test (HWFET) for E20 in comparison with unleaded regular gasoline. For the same vehicle, the highway fuel economy was greater than calculated for all tested blends, with an especially high peak at E20. The new study, co-sponsored by the U.S. Department of Energy (“DOE”) and the American Coalition for Ethanol (“ACE”), also found that mid-range ethanol blends reduce harmful tailpipe emissions.

Rapid expansion of the ethanol industry is creating global supply/demand issues. In some geographical areas, like the U.S. for example, supply is outgrowing demand. This is having a negative effect on the price of ethanol for producers and sustainability of the ethanol industry. Due to emissions and durability testing requirements, ethanol producers are having difficulty with assessing the economic and environmental impacts of midlevel anhydrous ethanol blends on current auto engines in order to increase blending rates and the RFS. In contrast to higher percentage anhydrous ethanol blends, HE15 and higher blends can be utilized in legacy vehicles (existing auto engines) as well as FFVs. Once parallel testing has been conducted for midlevel and E85/HE85 anhydrous and hydrous ethanol blends, further fuel efficiency and emissions testing may not be necessary. In addition to raising blending rates and the RFS, the high price of corn and competition between food and fuel is squeezing profit margins of ethanol producers, resulting in global inflation of fertilizers, and reducing food supplies for staple food products including rice, corn, potatoes and wheat. Hydrous ethanol blends could reduce some of this inflationary pressure by increasing efficiencies of production.

A 3-6% increase in ethanol production accompanied by a decrease in energy costs, plus an increase in fuel efficiency, will help to increase ethanol sales and profit margins for ethanol producers. Existing gasoline pipelines will be able to utilize midlevel hydrous ethanol blends as a much more compatible blendstock. This will dramatically reduce transportation costs by allowing petro-refineries and blenders to leverage existing infrastructures for distribution of hydrous ethanol. New turbocharged engines designed for ethanol only, FFV, and ethanol hybrid vehicle technologies allow for utilizing hydrous ethanol in E85 and E100 fuels in conjunction with electric power to provide unprecedented power, fuel efficiency and emissions reductions. Such combinations can substantially reduce and eventually eliminate dependence on fossil fuels.

In summary, a transition from anhydrous to hydrous ethanol for gasoline blending is expected to make a significant contribution to ethanol’s cost-competitiveness, fuel cycle net energy balance, and greenhouse gas emissions profile.

Hi,
I am a PhD student from Michigan Technological University. I am looking for latent heat of vaporization(LHV) of Ethanol at various pressures. I am also looking for LHV of gasoline and gasoline-ethanol blends. Do you, by any chance, happen to know where can i find LHV values at different saturation pressures. Your response will be greatly appreciated.

I am told that you should google "latent heat vaporization ethanol"...and gasoline and water, etc. There is lots of stuff there. Hal