| DIESEL FUEL
Diesel fuel consists of a large number of ‘hydrocarbons' and is obtained by distillation of crude oil. It is organic in nature and due to oxidation will degrade over time.
Water is present in diesel fuel in very small quantities [approx 80 parts per million]. This is known as ‘dissolved water' and occurs where the water has been chemically dissolved in the fuel,like sugar in coffee. The warmer the fuel the more water will be dissolved. With increased temperature there is a corresponding increase in solubility as water is absorbed from the atmosphere. But as the temperature drops the water will come out of solution in the form of ‘free water'.
‘Free water' occurs where the water is separated from the fuel and usually is found on the bottom of fuel/storage tanks. Water condenses on the walls of the fuel/storage tanks due to temperature changes. It has been estimated that in a 5000 litre storage tank, as much as 20 litres of water can condense from the air during one year!
‘Emulsified water' occurs where the water is suspended in the fuel like oil and vinegar in salad dressing. It is necessary to use a demulsifier agent to pull out the water and convert it to free water.
‘Paraffin' is inherent in all diesel fuels and varies in amount depending on the crude oil source. Paraffins positive aspect is its ‘btu' content i.e. engine power.
However in cold temperatures paraffin crystallises into wax which can block fuel filters and result in engine shutdown.
‘Fuel pour point' is the temperature at which the paraffin content solidifies such that the fuel will not pour under its own weight.
This is also referred to as the ‘cfpp'-cold filter plugging point.
‘Fuel cloud point' is the temperature at which the paraffin content in the fuel begins to congeal [changes into visible wax] causing the liquid to appear ‘cloudy'.
'Cetane number' is the measure of the ignition quality of diesel fuel [its readiness to burn in the combustion chamber] low cetane ratings will cause diesel knock due to ignition delays. Normally minimum 45.
‘Flash point' is the temperature at which fuel starts to give off a vapour which would ignite immediately if lit by spark or flame.e.g.In Australia, minimum specified by Shell is 64C
‘Self ignition temperature' is the temperature at which atomised fuel will ignite without the aid of a spark and is normally around 250C
‘Blending' is the mixing of different types of fuel. A good example is diesel fuel and kerosene. This practice is carried out by unscrupulous Operators who purchase the kerosene as a no excise [tax] item so they can then dilute the high excise [tax] diesel fuel and then sell the blend as diesel fuel. The result is drop in power, hard starting, poor fuel economy and diminished lubricating quality which results in high wear of components.
It should be noted that adding kerosene to diesel fuel will lower the ‘pour point and ‘cfpp'.
‘Fungal growth' can appear in fuel/storage tanks in extreme situations. The following description sounds like the script from a ‘monster movie. Several forms of fungi can survive and multiply in diesel fuel. They grow into long strings and form larger globules and are of slimy appearance and are black,green or brown in colour!!
The most effective treatment is with a ‘biocide' but be warned biocides are environmentally unfriendly and must be used with great care and respect for natural resources. 01/03/99
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