Numerical simulation of combustion process in vaporized/mixed fuel vehicle air heater combustion chambers was conducted with software "FIRE" developed by AVL company.The simulation models adopted were: Wall Film model for fuel evaporation,Coherent Flame model for combustion,Zeldovich model for NO_x and FIRE model for soot formation.Simulation results show that the air inlets of the first ring are crucial to vaporized fuel concentration field.As the air inlet diameters increase,the intake central swirl is intensified and thus fuel evaporation in the first combustion chamber is improved.Combustion mostly happens in the second combustion chamber.Tangential intake results in intensified central swirl,which causes the high temperature zone to concentrate around the longitudinal axis of the second combustion chamber.The highest soot formation rate appears at the circumferential swirl zone in the first combustion chamber and the high temperature zone in the upper half of the second combustion chamber.As the peak temperature in the combustion chambers is below the NO_x formation criteria, only very few NO_x is formed.