In this paper, evaporation of heavy fuel oil (HFO) droplet under atmospheric pressure is studied through a fully transient approach. The HFO is considered as a multi-component liquid with temperature-dependent properties. The performance of this fully transient approach is evaluated for different fuels and results are compared with available experimental data for gasoline and diesel fuel. The comparison shows excellent agreements, and also reveals the flexibility of this approach for interpretation and justification of the evaporation process details by using of internal distribution of temperature and composition. Based on distillation curve, several multi-component compositions are presented for the HFO. The composition is broken down into several pseudo-components and the effects of number of components and their method of selecting are studied comparatively. It shows that despite the wide range of compositions of heavy fuels, a compound consists of a few numbers of pseudocomponents can be a suitable representative for them. Also pseudo-components should be chosen with equal interval temperature and narrow boiling temperature range. The effects of environment temperature on the evaporation of droplets are investigated in a parametric study. The results show that internal temperature distribution is not very sensitive to the ambient temperature due to the high boiling temperature of heavy components of the fuel. Also wide span of temperature in the heavy fuel droplet makes it possible to predict the initial condition of pyrolysis and thermal cracking of heavier components.