<p>This study investigates the effect of radiation heat transfer and participating media (gray and non-gray) on temperature distribution and heat flux to the wall surfaces of a direct injection combustion chamber. In this study, a diffusion flame in a cylindrical geometry was modeled and all phenomena such as combustion, combined heat transfer and turbulence are considered. Moreover, the radiation heat transfer is solved for gray and non-gray participating media. The solution was verified by experimental data. The results show that ignoring radiation effects may lead to 30% error in combustion chamber pressure and 38% error in combustion chamber temperature calculations. In addition, ignoring non-gray media (gray assumption) causes up to an 11% error in combustion chamber pressure and a 7% error in temperature. Finally, results of this study show that, in combustion chamber studies ignoring radiation, participating media and non-gray effects will lead to error, especially when both the temperature and concentration of non-gray gases are high so combustion chamber modeling requires the inclusion of radiation in order to be relatively accurate. The model presented in this study presents a new framework for future studies of heat transfer in internal combustion engines.</p>