Conjugate radiation-convection heat transfer in a combustion chamber is considered. Radiation in emitting absorbing medium is coupled with general heat convection problems. While the radiation solver is an in-house BEM (Boundary Element Method) based code, heat convection is modelled using a commercial package. A procedure of acceleration of the ray tracing in ortho cartesian and cylindrical meshes is developed, significantly increasing the numerical efficiency of the radiative solver. The developed procedure is compared with a series of benchmarks and applied to the simulation of the radiative heat transfer within combustion chamber fired with natural gas. Good agreement with standard Discrete Ordinates solvers is observed.