A Numerical Study of the Influence of Transport Properties of Inert Diluents on Soot Formation in a Coflow Laminar Ethylene/air Diffusion Flame

The influence of transport properties of inert additives on soot formation in a coflow axisymmetric ethylene/air diffusion flame has been numerically investigated. Detailed reaction mechanism and complex thermal and transport properties were used. The fully coupled elliptic equations were solved. The radiative heat transfer from CO, CO2, H2O, and soot was calculated using the discrete-ordinates method coupled with a SNBCK-based wide-band model. A simplified two-equation soot model was used. The interactions between the soot and gas-phase chemistry were taken into account. The effects of adding argon and helium to either the fuel or the oxidant were determined. The results show that the effects of argon and helium addition on soot formation process in a laminar ethylene/air diffusion flame are different because of the difference in their transport properties. When they are added to the fuel, argon is found to be more efficient at suppressing soot formation than helium due to the temperature difference caused by the different thermal diffusivities. However, when they are added to the coflow air, it is found that although both temperature and concentration modifications cause helium to be more efficient at suppressing soot formation than argon, it is the temperature modification that is more significant.