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D I S E L F U E L S ( H S D / L D O )

POUR POINT

The pour point of a fuel is the lowest temperature at which it will pour or flow when chilled under prescribed conditions. It is a very rough indication of the lowest temperature at which a given fuel can be readily pumped. However, since practical conditions are quite different from those under which the laboratory test is conducted, many fuels can be pumped at temperatures well below their laboratory pour point.

Sometime cloud point is measured. This is the temperature at which paraffin wax begins to crystallise or separate from solution when the fuel is chilled under prescribed conditions. This may settle out in the fuel system and cause blockage of filters - leading to malfunctioning or stalling of the engine.

COLD FILTER - PLUGGING POINT

The cold filter plugging point (CFPP) is defined as the highest temperature at which the fuel, when cooled under prescribed conditions, either will not flow through the filter (45 microns) or will require more than 60 seconds for 20 ml to pass through. This is the temperature at which wax crystals begin to cause blockage of filter.

FLASH POINT

This ha no bearing on performance but is important largely from the point of view of safety in handling the fuel and minimum values are usually specified in the specification.

The flash point of High speed diesel is stipulated as min. 32 deg C and thus it falls under the category of class 'B' of petroleum products. While other diesel fuels have a flash point of min. 66 deg. C and hence fall in the category of class 'C' of petroleum products.

SPECIFIC GRAVITY

This is defined as the ratio of the weight of a given volume of oil to the weight of the same volume of water at a given temperature. Another index for measuring this characteristic is by Density, mass per unit volume at a standard temperature. Specific Gravity / Density is of limited usefulness as a direct measure of diesel fuel quality. However, it provides a convenient means of controlling product uniformity in refinery operations and of converting volume to weight. Variations in specific gravity affect the volumetric fuel consumption of an engine, since the higher the specific gravity the higher the heat content in a unit volume of the fuel. However this is not significant in use unless the variations are very large.