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

Abstract

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 (X_NH3) 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 + O₂O + OH and R1927: NH₂ + NHN₂H₂ + 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.