The chemical diversity of the components in bio-oil has a significant effect on its evaporation. The low boiling point compounds, such as simple acids and water, evaporate away from the surface at a faster rate than the internal diffusion. As a result a significant proportion still remains in the droplet core late in the evaporation process. As the droplet temperature increases, these trapped chemicals, in the centre of the droplet, can reach a sufficiently high temperature to cause them to vapourise resulting in rapid expansions, which can fracture the droplet. In this study a numerical model of a stationary, spherically symmetric evaporating bio-oil droplet, in a hot ambient atmosphere, is used to investigate the effect of the rate of diffusion on the evaporation process. (C) 2010 Elsevier Ltd. All rights reserved.