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SUPERIOR KEROSENE (SKO)

DEFINITION

A refined petroleum distillate, less volatile than gasoline, boiling between 150 0C and 300 0C, its distillation range overlapping that of gasoline and HSD.

SPECIFICATIONS

Superior kerosene meets Bureau of Indian Standards specification IS : 1459-1974.

SMOKE POINT

The maximum flame height in millimeters (mm) at which the oil burns without smoking when tested in a standard wick-fed lamp under specified conditions is termed and smoke point.

Smoke point is important because it determines the degree of illumination possible from a given kerosene in a wick-fed lamp. Smoke point is related to the hydrocarbon composition of kerosene - it is highest with paraffins, considerably lower with naphthenes and very much lower with aromatics. The smoke point is also an indication of the tendency to smoke when the flame is smaller than the maximum stipulated size. Smoking under such conditions is usually caused by an inadequate supply of air or by a sudden draught.

Excise/Customs requirements stipulate a minimum flame height of 18 mm mainly to distinguish it from HSD. The Indian customs method for testing smoke point tends to give somewhat lower readings than the standard IP method.

BURNING TEST : CHAR VALUE

It is important that kerosene should burn freely and steadily for reasonable periods without attention to the appliance and with no diminution of flame. Burning tests have been developed to assess these properties.

The burning  test is carried out for 24 hours in a standard lamp with a flame conforming to a specified size and shape. At the end of the test the consumption of kerosene and the amount of char formed on the wicks are measured, while a qualitative assessment is made of the appearance and colour of any bloom which may have been formed on the chimney. The char value is expressed as milligrams of dry char per kilogram of kerosene consumed.

VOLATILITY

The nature of the distillation range is of significance with regard to burning characteristics, such as warming up time and initial flame size, etc. and it is customary to place suitable limits on volatility. An abnormally high final Boiling Point can indicate contamination with higher boiling constituents.

COLOUR

Colour in itself has no bearing on burning quality, but its measurement is useful in checking consistency of supplies and contamination.

SKO is water which when produced and is marketed as such in India. However, in many countries premium grades are dyed for ease of identification, the dye present in trace quantities.

SULPHUR

Only slight amounts of sulphur compounds remain in kerosene after refining which removes most of the undesirable products. Hydrogen sulphide and mercaptans are removed so as to render the kerosene marketable from the point of view of odour.

Free or corrosive sulphur in appreciable amount could corrode metallic components of an appliance, e.g. pressure burner vaporizing tubes which operate at high temperatures. The usual test applied in this connection is the Copper Corrosion Test. The total sulphur content of kerosene should be low because oxides of sulphur formed during combustion should not be present to harmful extent in the atmosphere. This is particularly important in respect of indoor burning appliances which are not provided with the flue. Also, as mentioned earlier a higher sulphur content can contribute to the formation of lamp chimney deposits.

FLASH POINT

In the interest of safety, legislation has been introduced in most countries fixing minimum flash point limits to prevent the inclusion of highly inflammable volatile fractions in kerosene distillates. According to Controller of Explosives classification it falls in the category of Class B Petroleum Products. Its flash point (Abel) is stipulated as Min. 35 deg C in the IS specification.

SPECIFIC GRAVITY

As with colour, specific gravity has no relation to burning quality, but it is a useful aid for quantity reckoning and identity.