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.

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 our MAN medium speed liquid fuel engines  can burn heavy fuel oil (HFO). Of course, our medium speed dual  fuel engines are capable of burning HFO in liquid fuel mode as well.

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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