Especially NE and Mid Atlantic and Texas
http://www.eia.doe.gov/pub/oil...6.pdf
http://lfee.mit.edu/public/LFEE%202006- ... ter.htmlIf you only have a small quantity of water, then the addition of 500mls ofdry isopropanol (IPA) to a near-full 30-40 litre tank will absorb the water,and will not significantly affect combustion. Once you have mopped up thewater with IPA, small, regular doses of any anhydrous alcohol will helpkeep the tank dry. This technique will not work if you have very largeamounts of water, and the addition of greater amounts of IPA may result inpoor driveability.
Water in fuel tanks can be minimised by keeping the fuel tank near full, andfilling in the morning from a service station that allows storage tanks tostand for several hours after refilling before using the fuel. Note thatoxygenated gasolines have greater water solubility, and should cope withsmall quantities of water.
[ end extract ]
So your question may be " why IPA, why not methanol or ethanol,which are usually cheaper ?". The answer is dependent on twoaspects, the actual ability to act as a cosolvent, and theeffect of temperature on the phase separation point of gasoline/cosolvent mixtures. The aromatics content of the fuel also hasa profound effect on the amount of water that can be tolerated,with 25% aromatics tolerating about 0.1% water and 40% aromaticstolerating about 0.2% water at 15C.
Adding 15% by volume of anhydrous methanol to a typicalnon-oxygenated gasoline will provide a water tolerance ( theamount of water that can be added before phase separation occurs )to around 0.16% at 15C, but at 0C the tolerance would be close to0%, ie the water/methanol would be a separate phase without theaddition of water. Adding more that 15% of methanol can adverselyaffect driveability on engines without management systems designedfor oxygenated fuels.
Adding about 3% by volume of anhydrous iso propyl alcoholwill provide a water tolerance of about 0.35% at 15C and about0.2% at 0C, thus it's ability as a cosolvent is superior ona volume basis, and far less temperature sensitive thanmethanol.
Ethanol is between the two, with a 15% blend tolerating about1% water at 15C. The best additives are the isomeric propyland butyl alcohols, and above them, the tolerance decreasesas the alcohols become less water miscible.
The above numbers are from memory, and are approximate, butyou get the general idea. The experiment is easy to do if youwant real numbers for your local gasoline. Take 100 mls ofgasoline ( remembering that it's highly flammable ) in astoppered glass measuring cylinder and measure temperature.
Add one drop ( ideally a 1ml syringe, but any narrow tubing ordropper can be used, and use 20 drops of water = 1 ml ), stopper,and shake. If the solution goes hazy, warm slightly in a bucketof warm water and measure the temperature that it clears.If it stays clear, reseal and put it in a fridge or freezer ( ina container that will contain the fuel should the glass break- and remember that all vapour will be flammable and that thecontroller and light use non-flameproof switches ).
When hazy, remove and record temperature that the haze clears,and if it's still clear, add another drop and repeat.
Now repeat adding 5,10,15% anhydrous MeOH, EtOH, or IPA ( rememberingthat many IPA products ( eg as an antistatic ) actually are notanhydrous, and can contain up to 40% water - which somewhatdefeats the purpose :-) ). You can draw a graph of water toleranceversus temperature that shows the different positions and gradientsof the alcohols.