What is LDO (LIGHT DIESEL OIL)?

It is low viscosity fuel recommended for slow speed diesel engines operating below 750 rpm used in agriculture, marine and industrial sectors. It is also used as a fuel in certain specialized industrial application. It meets IS 1460 1974, grade LDO specification.

NOMENCLATURE

LDO is a blend of distillate fuel with a small proportion of residual fuel.

CETANE NUMBER

The most accurate method of assessing the ignition quality of a diesel fuel is by measuring its cetane number
in a test engine, the higher the cetane number the higher the ignition quality. The cetane number of a fuel is defined as the percentage of cetane, arbitrarily given a cetane number of 100, in a blend with alphamethyl-naphthaline (cetane number -0), which is equivalent in ignition quality to that of the test fuel. Typical cetane number of LDO is around 35 – 38.

VISCOSITY

Defined simply, viscosity means resistance to flow or movement. In metric system, centistoke is the unit for
its measurement. It is function of time taken in seconds for a given volume of oil to flow through a calibrated viscometer under specified conditions. Viscosity depends on temperature and decreases as the temperature increases, so no numerical value has any meaning unless the temperature is specified.

CARBON RESIDUE

Different fuels have different tendencies to crack and leave carbon deposits when heated under similar conditions. This property is normally measured by the Conradson or the Ramsbottom coke tests. In these tests,
a sample of the fuel is heated without contact with air under specified conditions and the weight of carbon residue remaining after the test is expressed as a percentage of the weight of the sample. 

VOLATILITY

As a rule, the higher the viscosity of a liquid fuel, the lower its volatility. Therefore provided the viscosity lies within specified limits, a satisfactory volatility is automatically ensured. However, the percentage recovered at some particular temperature e.g. 366 deg C, is specified in the case of HSD mainly to control engine fouling
due to incomplete combustion of the higher boiling components.

TOTAL SULPHUR

This is significant because it governs the amount of sulphur oxides formed during combustion. Water from combustion of fuel collects on the cylinder walls, whenever the engine operates at low jacket temperatures. Under such conditions, sulphurous and sulphuric acids are formed, which attack the cylinder walls and piston rings, promote corrosion, and thus cause increased engine wear and deposits.

Typical Sulphur content in LDO is 1.8% w/w.

ACIDITY

This should be low in order that corrosion of metals in contact with the fuel during storage and distribution is minimised.

INORGANIC OR MINERAL ACIDITY

Where diesel fuels are treated with mineral acid as part of the refining procedure, traces of mineral acid remaining in the final product would obviously be undesirable. Hence, zero limit is usually specified for this property.

ORGANIC ACIDITY

This is due to the naphthenic type which are constituents of crude petroleum. Their presence in small amounts
is not necessarily an indication of improper refining or poor quality. Although much weaker than mineral acids, they may attack galvanised metal and this is why the use of galvanised containers for the storage of diesel fuels is not recommended.

ASH CONTENT

Ash is a measure of the incombustible material present in a fuel and is expressed as a percentage of the weight of the fuel sample. In the case of distillate fuels, it usually consists of rust, tank scale or sand, which settles
out readily. Blends of distillate and residual fuel, e.g. LDO may additionally contain metal oxide derived from oil soluble and insoluble metallic compounds. Ash is significant because it can give rise to deposit problems such
as abrasion, malfunctioning of injectors and high temperature corrosion, particularly with residual fuels. Typical
Ash content is 0.02% w/w.

SEDIMENT AND WATER

These are absolutely undesirable contaminants and should be as low as possible. The higher the specific gravity and viscosity of a fuel, the greater the quantities of water and sediment it can hold in suspension. Large quantities of sediment can affect the combustion of the fuel, and if abrasive, may cause excessive wear of closely fitting parts of fuel pumps and injectors. It may also clog filters and build up deposits in tanks and
piping. Typical Water content in LDO should not exceed 0.25% w/w and sediment content should not exceed
0.1% w/w.

CALORIFIC VALUE

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one-kilogram weight of fuel. Gross calorific value is higher than net calorific value to the extent of heat required to change water formed by combustion into water vapours

Typical Gross Calorific Value of LDO varies between 10200-10800 Kcal/Kg.

TYPICAL COMPOSITION

LDO has higher C/H ratio than Furnace Oil.

B.I.S specification Chart