To model combustion, the information related to the fluid mechanics of the system must be known. All the transport phenomena such as convection, diffusion as well heat should be accurately incorporated in such models. Chemical reaction schemes must also be known so as to estimate the formation of combustion products and species and also to predict ignition, stabilization and extinction of flames. Radiation also takes place due to presence of soot formed during combustion and also there is radiative heat transfer from wall of the combustion chamber. Combustion of fuels comes under multiphase system, where liquid fuels is a two phase system consisting of liquid and gas phases while solid fuel belongs to a three phase system. The challenges faced are to model breaking up of the liquid fuel, its reaction and distribution of the reactants in three dimensional spatial systems. These models which form part of CFD, has become an indispensable tool for combustion modelling.