Thermodynamics second-law analysis of hydrocarbon diffusion flames: Effects of soot and temperature

In this paper, a computation of the ethylene co-flow diffusion flame is carried out using the Co-flame code with a detailed gas-phase mechanism and soot model. A numerical analysis based on the thermodynamics second-law was conducted for developing a high-efficiency combustion condition of hydrocarbon diffusion flames. The entropy generations and exergy loss ratios due to thermal radiation, heat conduction and convection, and chemical reactions are numerically calculated, in which entropy generations caused by both gasses and soot particle are considered. The effects of soot (controlled by changing stoichiometric mixture fraction Zst from 0.1 to 0.62) and adiabatic flame temperature Tad (2300 K, 2500 K, 2700 K) on entropy generation and exergy loss ratio in flame are investigated. The results suggest that, entropy generation due to soot radiation and soot surface growth and oxidation accounts for about 15% and 5% in total radiation entropy generation and total chemical entropy generation, respectively. Entropy generation due to thermal radiation decreases when soot reduces, and entropy generation due to heat conduction and convection, mass diffusion and chemical reactions increases when Zst increases. When Tad is 2300 K, the change of exergy loss ratio is slight with a reducing of soot and increasing of Zst. When Tad is 2500 K and 2700 K, the exergy loss ratio has tendency of increasing with a reducing of soot and increasing of Zst. The exergy loss ratio increases with increasing of Tad.