Commercial liquid petroleum fuels are complex mixtures of various hydrocarbons. In multicomponent fuel modelling, these liquid fuels are represented typically with two components or up to ten discrete components. Even with ten components, there are limitations on the representation of real commercial fuels such as heavy fuel oil (HFO), which contains large numbers of hydrocarbons with a wide range of molecular weights and dissimilar structures. Continuous thermodynamics and pyrolysis chemical kinetics are used to model the behaviour of HFO in diesel spray combustion.