The importance of radiative heat transfer on the combustion and soot formation characteristics under nominal ECN Spray A conditions has been studied numerically. The liquid n-dodecane fuel is injected with 1500 bar fuel pressure into the constant volume chamber at different ambient conditions. Radiation from both gas-phase as well as soot particles has been included and assumed as gray. Three different solvers for the radiative transfer equation have been employed: the discrete ordinate method, the spherical-harmonics method and the optically thin assumption. The radiation models have been coupled with the transported probability density function method for turbulent reactive flows and soot, where unresolved turbulent fluctuations in temperature and composition are included and therefore capturing turbulence-chemistry-soot-radiation interactions.
Results show that the gas-phase (mostly CO2 ad H2O species) has a higher contribution to the net radiation heat transfer compared to soot. The effect of radiation absorption was found to be important and the typical radiation time scale is observed to overlap with the long injection duration, leading to a moderate influence on the temperature distribution. The flame lift-off length is not affected by radiation and differences in soot formation are perceivable but only minor. The performance of the DOM and P1 models is comparable, whereas the optically thin assumption leads to a higher cooling effect. It is anticipated that NOx formation rates are expected to be influenced by radiative heat transfer in a more pronounced manner.
