Fuel oil, (also known as marine fuel or furnace oil) is a fraction obtained from petroleum distillation, either as a distillate or a residue. Broadly speaking, fuel oil is any liquid fuel that is burned in a furnace or boiler for the generation of heat or used in an engine for the generation of power, except oils having a flash point of approximately 40 °C (104 °F) and oils burned in cotton or wool-wick burners. In this sense, diesel is a type of fuel oil. Fuel oil is made of long hydrocarbon chains, particularly alkanes, cycloalkanes and aromatics. The term fuel oil is also used in a stricter sense to refer only to the heaviest commercial fuel that can be obtained from crude oil, i.e., heavier than gasoline and naphtha.
In Australia the term “distillate” refers specifically to diesel fuel.
Although the following trends generally hold true, different organizations may have different numerical specifications for the six fuel grades. The boiling point and carbon chain length of the fuel increases with fuel oil number. Viscosity also increases with number, and the heaviest oil has to be heated to get it to flow. Price usually decreases as the fuel number increases.
Number 1 fuel oil is a volatile distillate oil intended for vaporizing pot-type burners. It is the kerosene refinery cut that boils off right after the heavy naphtha cut used for gasoline. Older names include coal oil, stove oil and range oil.
Number 2 fuel oil is a distillate home heating oil. This fuel is sometimes known as Bunker A. Trucks and some cars use similar diesel fuel with a cetane number limit describing the ignition quality of the fuel. Both are typically obtained from the light gas oil cut. Gas oil refers to the original use of this fraction in the late 19th and early 20th centuries – the gas oil cut was used as an enriching agent for carburetted water gasmanufacture.
Number 3 fuel oil was a distillate oil for burners requiring low-viscosity fuel. ASTM merged this grade into the number 2 specification, and the term has been rarely used since the mid-20th century.
Number 4 fuel oil is a commercial heating oil for burner installations not equipped with preheaters. It may be obtained from the heavy gas oil cut.
Number 5 fuel oil is a residual-type industrial heating oil requiring preheating to 170–220 °F (77–104 °C) for proper atomization at the burners. This fuel is sometimes known as Bunker B. It may be obtained from the heavy gas oil cut, or it may be a blend of residual oil with enough number 2 oil to adjust viscosity until it can be pumped without preheating.
Number 6 fuel oil is a high-viscosity residual oil requiring preheating to 220–260 °F (104–127 °C). Residual means the material remaining after the more valuable cuts of crude oil have boiled off. The residue may contain various undesirable impurities including 2 percent water and one-half percent mineral soil. This fuel may be known as residual fuel oil (RFO), by the Navy specification of Bunker C, or by the Pacific Specification of PS-400.
Mazut is a residual fuel oil often derived from Russian petroleum sources and is either blended with lighter petroleum fractions or burned directly in specialized boilers and furnaces. It is also used as a petrochemical feedstock. In the Russian practice, though, “mazut” is an umbrella term roughly synonymous with the fuel oil in general, that covers most of the types mentioned above, except types 1 and 2/3, for which separate terms exist (kerosene and diesel fuel/solar oil respectively — Russian practice doesn’t differentiate between diesel fuel and heating oil). This is further separated in two grades, “naval mazut” being analogous to grades 4 and 5, and “furnace mazut”, a heaviest residual fraction of the crude, almost exactly corresponding to the number 6 fuel oil and further graded by viscosity and sulphur content.
CCAI and CII are two indexes which describe the ignition quality of residual fuel oil, and CCAI is especially often calculated for marine fuels. Despite this, marine fuels are still quoted on the international bunker markets with their maximum viscosity (which is set by the ISO 8217 standard – see below) due to the fact that marine engines are designed to use different viscosities of fuel. The unit of viscosity used is the Centistoke and the fuels most frequently quoted are listed below in order of cost, the least expensive first.
- IFO 380 – Intermediate fuel oil with a maximum viscosity of 380 Centistokes (<3.5% sulphur)
- IFO 180 – Intermediate fuel oil with a maximum viscosity of 180 Centistokes (<3.5% sulphur)
- LS 380 – Low-sulphur (<1.0%) intermediate fuel oil with a maximum viscosity of 380 Centistokes
- LS 180 – Low-sulphur (<1.0%) intermediate fuel oil with a maximum viscosity of 180 Centistokes
- MDO – Marine diesel oil.
- MGO – Marine gasoil.
- LSMGO – Low-sulphur (<0.1%) Marine Gas Oil – The fuel is to be used in EU community Ports and Anchorages. EU Sulphur directive 2005/33/EC
- ULSMGO – Ultra Low Sulphur Marine Gas Oil – referred to as Ultra Low Sulfur Diesel (sulphur 0.0015% max) in the US and Auto Gas Oil (sulphur 0.001% max) in the EU. Maximum sulphur allowable in US territories and territorial waters (inland, marine and automotive) and in the EU for inland use.
The density is also an important parameter for fuel oils since marine fuels are purified before use to remove water and dirt from the oil. Since the purifiers use centrifugal force, the oil must have a density which is sufficiently different from water. Older purifiers work with a fuel having a maximum of 991 kg/m3; with modern purifiers it is also possible to purify oil with a density of 1010 kg/m3.
The first British standard for fuel oil came in 1982. The latest standard is ISO 8217 from 2005. The ISO standard describe four qualities of distillate fuels and 10 qualities of residual fuels. Over the years the standards have become stricter on environmentally important parameters such as sulfur content. The latest standard also banned the adding of used lubricating oil (ULO).
for Fuel Oil analysis see the link below: