HFO, also known as “residual fuel oil”,
is based on the high viscosity, tar-like mass, which remains after the
distillation and subsequent cracking of crude oil in order to produce
lighter hydrocarbon products, such as petrol , distillate diesel fuels
and heating oil or feedstocks for lubricants.The main components are alkanes, cycloalkanes and different carbon hydrides. The boiling range is between 300°C and ~700°C.
Due to its semi-fluid consistence, HFO has to be preheated to make it combustible in engines.
RMA, RMB, RMD, RME, RMG or RMK are the international trade names.
Main ref : http://powerplants.man.eu/fuels/hfo
Another Ref : https://www.anton-paar.com/corp-en/products/applications/viscometry-of-heavy-fuel-oil-hfo-and-residual-fuel-oil-rfo/
Cheap, but challenging
As a residual product, HFO is a relatively inexpensive fuel – it typically costs 30% less than distillate fuels (MDO/MGO) (Verlinkung). It thus became the standard fuel for large marine diesel engines during the oil crisis in the 1970s and 1980s, and it required extensive adaptation of the injection system and other components of low and medium speed engines – which are still the only reciprocating engines capable of running on HFO.Most of MAN medium speed liquid fuel engines can burn heavy fuel oil (HFO). Of course, medium speed dual fuel engines are capable of burning HFO in liquid fuel mode as well.
What is HFO or RFO?
Fuel oil is a fraction obtained from petroleum
distillation, either as a distillate or a residue. Fuel oil is
classified in six classes, numbered 1 through 6, according to its
boiling point, composition and purpose.
- No.1 is similar to kerosene and is the fraction that boils off right after gasoline.
- No.2 is the diesel fuel that trucks and cars run on, leading to the name "road diesel".
- No.3 is a distillate fuel oil and is rarely used.
- No.4 fuel oil is usually a blend of distillate and residual fuel oils, such as No.2 and 6; sometimes it is just a heavy distillate (~ diesel distillate or residual fuel oil).
- No.5 is a mixture of 75-80% of No.6 and 25-20% of No.2.
- No.6 is called residual fuel oil (RFO) or heavy fuel oil (HFO). It is the remainder of the crude oil after gasoline and distillate fuel oils were extracted through distillation. It fuels thermal power stations or robust engines.
Why measure the viscosity and density of RFO?
The viscosity of an oil is a measure of its
resistance to flow. In fuel oil it is highly significant since it
indicates both the relative ease with which the oil can be pumped, and
the ease of atomization.
Density alone is of little significance as an
indication of the burning characteristics of fuel oil. Used in
conjunction with other properties, it is of value in mass-volume
relationships and for the specific energy of an oil.
Fuel oil specification
Heavy fuel oil
| ISO 8217, ISO-F-RM | K700 | |||||||||||||
| Fuel-system related characteristics values | ||||||||||||||
| Viscosity (at 50 °C) | mm2/s (cSt) | max. | 700 | |||||||||||
| Viscosity (at 100 °C) | mm2/s (cSt) | max. | 55 | |||||||||||
| Density (at 15 °C) | kg/m3 | max. | 1,010 | |||||||||||
| Flash point | °C | min. | 60 | |||||||||||
| Pour point | °C | max. | 30 | |||||||||||
| Hydrogen sulfide | mg/kg | max. | 2 | |||||||||||
| Acid number | mg KOH/g | max. | 2.5 | |||||||||||
| Total sediment aged | mass % | max. | 0.10 | |||||||||||
| Engine-related characteristic values | ||||||||||||||
| Carbon residues (Conradson) | m% | max. | 20 | |||||||||||
| Sulphur | m% | max. | 5 | |||||||||||
| Ash | m% | max. | 0.15 | |||||||||||
| Vanadium | mg/kg (=ppm) | max. | 450 | |||||||||||
| Water | Vol.% | max. | 0.5 | |||||||||||
| Additional parameters | ||||||||||||||
| Aluminium and silicon | mg/kg | max. | 60 | |||||||||||
| Asphalts | m% | max. | 2/3 of carbon residues (Conradson) | |||||||||||
| Sodium | mg/kg | Sodium < 1/3 vanadium, sodium < 100 | ||||||||||||
| Used lubricating oil (ULO) | mg/kg | Ca >30 and Zn >15 or CA >30 and P >15 | ||||||||||||
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