Soot formation in laminar ammonia-ethylene counterflow diffusion flames: Isolation of chemical, thermal, and dilution effects

This numerical study investigates the effect of ammonia (NH3) addition on soot formation in laminar ethylene counterflow diffusion flames (CDFs). A chemically inert species is used to isolate the chemical effect, while the thermal and dilution effects are isolated using the formation rate fitting method. The KM2-NH3 mechanism is constructed, demonstrating good applicability for modeling NH3-C2H4 CDFs. As the NH3 addition ratio (XNH3) increases, the peak temperature, benzene (A1) mole fraction, and soot volume fraction (SVF) decrease. The chemical effect of NH3 addition promotes temperature though R1: H + O2--O + OH and R1927: NH2 + NH--N2H2 + H. It also promotes A1 formation by boosting R298: 2C2H3-* A1, etc., and converts C4H6-13 to produce C3H3. However, it suppresses soot formation through surface growth SR42: open (se) + C2H2-* H (se) + 2C(B) + H. The dilution effect on suppressing A1 formation is stronger than the thermal effect. The thermal effect dominates the suppression of soot formation, and the chemical effect is stronger than the dilution effect at low X NH3 , while the opposite is true at high X NH3 .