The combustion and extinguishment of n-heptane droplets in air-diluent environments under reduced-gravity are studied, where carbon dioxide, helium and xenon are used as diluents. A gasification model employing the volume of fluid (VOF) method was developed and implemented into the CFD package FLUENT. The droplet evaporation, combustion and parasitic current were validated by comparing with the previous study. The numerical results agree well with experimental data. The Soret effect is predicted to sometimes be important during combustion, changing the flame temperature by several hundred degrees K in some cases. Transport of oxygen to the flame is weakened by thermal diffusion if helium is used as a diluent gas, while it is strengthened by thermal diffusion if xenon is introduced. (C) 2010 Elsevier Ltd. All rights reserved.