Sport_Pilot
Posts: 7412
Joined: 1/21/2002
From: Acworth,
GA, USA
Status: online
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Well I don't think any of us want water in our fuel. After we want to burn our fuel and water doesn't burn nor lubricate our engines, so of course the manufactures want their fuel as pure as possible. Obviously our engines will not run on water! The lady wanted to know how much water is a problem. You stated that any water is intolerable. So I guess I should throw out my fuel after the first use? Because you will have water in the fuel the first time you use it. Even if you were to manage to get your pump attached to the fuel can without opening it you will encounter the greatest source of water when you defuel your plane. Since much of our fuel is converted to water when we burn it the muffler pressure has a lot of steam in it. This of course gets into the fuel in our tanks, and is then transfered back to our fuel can when we defuel the plane. So since most of us defuel our plane several times on each gallon of fuel and ususally without having problems. So this is proof that our engines can tolerate at least some water in our fuel, the question asked was how much.
You state that water is incompressable, this is true but our fuel is incompressable also, that is why we get hydralic lock when the cylinder is full of fuel, because it is incompressable. In fact it is one of the descriptions defining liquids and gasses, liquids are incompressable and gasses are compressabel. Now water has as a gaseous form also, it is called, well you know, steam. You also state that water will raise the compression in the engine. The law of partial pressure say's this isn't so. Steam is very compressable and only somewhat denser than our fuel.
To put it anouther way. You take a cylinder of fuel, air, and water vapor at 14.7 psi absolute, this is our average air pressure. Now take away the water and put it into a cylinder of perfect vacume. Now maybe it has a pressure of maybe .5 PSIA that means the pressure of the remaining fuel is 14.2 PSIA. Now you compress each gas to a compression ration of 10 to 1. Now the water vapor is 5 PSIA and the fuel and air is 142 PSI Put the water vapor back into the engine cylinder and the pressure is 147. Thats 10 times 14.7 so it is still a compression ratio of 10 to 1. So water doesn't change the compression ratio. This is the law of partial pressures.
Downunder has it right! In fact the early turbocharged GTO had a water injector to prevent detonation from the boost of the turbocharger. It was I think the first production car with a turbocharger. Actually the injector used a mixture of water and alcohol, but in a pinch pure water would work. Also I recall LF posted a site on racing fuel a while back and water was one of the additives mentioned to reduce detonation, along with acetone, and more exotic additives. Not all of these were for detonation I think.
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Moisture in Methanol - 
What kind of problems are you having - 
