Heavy fuel oil combustion modelling using continuous thermodynamics

Global shipping uses Heavy Fuel Oil (HFO) as the primary fuel. HFO is a mixture of oil refinery residue and cutter stock, hence it contains large numbers of hydrocarbons with a wide range of molecular weights and dissimilar structures. Conventional thermodynamics modelling techniques are inadequate for HFO vaporisation modelling. The present article summarises continuous thermodynamics vaporization models along with chemical kinetics models for decomposition and polymerisation, and soot burnout models, employed to study the behaviour of HFO spray combustion. A sample of HFO is also characterised in the laboratory using chemical characterisation procedures including sequential elution solvent chromatography, gas-chromatography mass spectrometry and elemental analysis, to obtain the composition and mean molecular weights of HFO fractions required for continuous thermodynamics modelling. Models are implemented via subroutines in a diesel spray simulation in the CFD package STAR-CD. The simulation is applied to a constant volume spray combustion chamber. The present model accounts for the formation and burnout of liquid phase soot in diesel engines. This soot will be emitted as Black Carbon if unburnt. The models are examined for two representative fuel samples; one with the good combustion quality and the other with poor. Good qualitative agreement is shown between the simulations and published experimental data.