Fuel and Water

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Fuel and Water

They don't mix and you shouldn't try to make them.

One of the more interesting characteristics that is shared by diesel, biodiesel, gasoline, and gasohol is that all these fuels are hygroscopic.

Hygroscopy is the ability of a substance to attract water molecules from the surrounding environment through either absorption or adsorption.

Some examples of this phenomenon are that Ultra-Low Sulfur Diesel (ULSD) will hold approximately 2/10 of 1% dissolved water. This may not sound like much, but if you do the numbers they show that 2/10 of 1% equals 2 gallons of water dissolved in 1000 gallons of fuel. If you work backwards, that would equal 1 gallon of water in 500 gallons of fuel, or 1 quart (32 ozs.), in 125 gallons, or 1 pint (16 ozs.), in 62.5 gallons, down to about 8 ozs. in a 30 gallon tank.

That much water can cause severe corrosion of fuel system components such as injectors, pumps, connectors, and even metal fuel tanks.

That level of water speeds the oxidation and chemical breakdown of the fuel.

That level of water is enough to encourage the growth of bacteria and fungi.

One of the most insidious characteristics of water dissolved in fuel is that the fuels ability to hold water is dependent on temperature. Simply put the warmer the fuel (up to a point) the more water it hold.

What often happens is that fuel stored for example at 60F will absorb that 2/10% water then as the fuel in a vehicle gets colder more and more of that water is pushed out of the fuel becoming liquid water droplets.

These droplets can collect in filters and if the temperature drops below 32F those droplets turn to ice crystals quickly plugging filters and causing other problems.

Fuel at 28F can hold approximately 1/2 as much water as fuel at 60F.

This means that you can have clear fuel with no liquid water at 60F and if the temperature drops sufficiently, you can have large amounts of free water suddenly appear as the temperature drops.

To make matters worse biodiesel can pickup and hold 10 times as much water as ULSD. So adding 2% or 5% biodiesel to regular diesel can dramatically increase the level of dissolved water.

Gasoline containing Ethanol suffers the same problem.

A 10% Ethanol blend can hold 3.8 teaspoons of dissolved water at 60F.

However if more water is added or if the temperature drops significantly this fuel suffers a problem called "Phase Separation".

In Phase Separation the dissolved (or liquid) water binds to the Ethanol and this Water/Ethanol mixture will drop out of the fuel.

This has a series of negative affects on the fuel quality and can have catastrophic effects on engines.

We will discuss more about this later.

We look forward to your comments and questions.

Diesel Doctor

Copyright 2009



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Last modified: 04/06/09
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