Effects of NH3 and H2 addition on morphology, nanostructure and oxidation of soot in n-decane diffusion flames

Abstract

The effects of ammonia and hydrogen addition on soot formation characteristics in n-decane laminar diffusion flames were studied. The addition of argon was specifically considered to identify the chemical effect of ammonia. The flame temperature, particle morphology, and oxidation characteristics were analyzed. Results showed that both ammonia and hydrogen addition increase the flame height and suppress soot formation, while the suppression effect of ammonia is more pronounced. The addition of argon or ammonia reduces the temperature of flame upstream and yields the similar flame temperature, while hydrogen addition increases the flame temperature. Compared to the flame with argon, the addition of ammonia delays particle nucleation, indicating that the soot nucleation and growth process are chemically inhibited. In contrast, doping hydrogen leads to an earlier nucleation process and aggregation phenomenon. Further analysis on particle nanostructure indicated that the addition of ammonia yields shorter lattice fringes, larger interlayer spacings and amorphous carbon contents, demonstrating a looser and higher disorder internal structure. The addition of hydrogen yields longer fringes and smaller interlayer spacings, showing the particles have a more compact internal structure and higher degree of graphitization. This indicates hydrogen addition reduces the oxidation activity of the particles, which is confirmed by thermogravimetric analysis.