Chemical characterization of heavy fuel oil for combustion modelling

The high demand of road transport has forced the oil refining industry to produce gasoline and diesel in greater quantities. Consequently large marine engines, which employ Heavy Fuel Oil (HFO), a mixture of oil refinery residue blended with cutter stock, as a fuel are receiving more carbon rich and higher aromatic content fuel causing serious problems such as piston ring wear, cylinder liner scuffing, solid deposition, exhaust valve sticking. HFO contains thousands of different components, hence classical thermodynamics modelling is inadequate and an alternative approach such as continuous thermodynamics is required to model multicomponent fuel. This paper outlines procedures for determining the chemical composition of HFO by separating it into chemical fractions differing in chemical composition and physical properties, and subsequent analysis. Sequential elution solvent chromatography was used to separate HFO into Saturates, Aromatics, Resins and Asphaltenes. Gas chromatographic analysis is insufficient to determine the overall composition of HFO, because most of the heavy compounds are not sufficiently volatile. Subsequent mass spectrometric and elemental analysis showed a wide range of molecular weight distributions for the fractions. The results also indicate that the saturates fraction contains cyclic structures with aliphatic side chains while the aromatics fraction contains tetracyclic aromatic rings with aliphatic side chains.