Effects of ammonia addition on soot formation in ethylene laminar premixed flames

This paper presents particle size distributions and chemical compositions of soot measured using a Scanning Mobility Particle Sizer (SMPS) and a Fourier-Transform Ion Cyclotron Resonance Mass Spectrometer (FT-ICR-MS), respectively, in flames of ethylene-oxygen and ethylene-oxygen doped with ammonia. The inhibitory effect of ammonia addition on soot formation in ethylene flames, as well as the influence on soot particle size are discussed. The results of particle size distributions showed that doping with ammonia decreases soot particle size and the volume fraction of soot particles. In this work, the flames were carefully studied under similar temperature conditions, so all observed changes could be attributed to chemical effects. The results of FTICR-MS analysis showed that polycyclic aromatic hydrocarbons (PAHs) were the main compositions in both pure ethylene and ammonia doped ethylene flames. Nitrogen-containing PAHs (N-PAHs) did not contribute significantly to soot nucleation or mass growth processes. Chemical kinetic analysis revealed that CN species generated in ethylene-ammonia flames removed carbon from participating in soot precursor formation, thereby reducing soot formation.