Sooting structure of methane counterflow diffusion flames with preheated reactants and dilution by products of combustion

Numerical and experimental study of the influence of CO2 and N2 dilution on soot formation in laminar coflow C2H4/air diffusion flames at pressures between 5 and 20 atm

“…The soot model used by Guo and Smallwood was a modified version of Appel et al [13] to improve the soot concentration prediction in the flame centerline region. Based on their numerical results Guo and Smallwood [12] concluded that the chemical suppression effect of CO 2 addition on soot formation is through reducing soot inception and surface growth rates, but not through enhancing soot oxidation associated with the enhanced OH radical concentrations suggested in earlier studies [3,[5][6][7][9][10][11]. The findings of Guo and Smallwood are consistent with the experimental measurements of Oh et al [10,11], who observed reduced soot number density in soot inception regions and smaller primary soot particle diameters.…”

“…The nature of the chemical effects of CO 2 on soot formation suppression, however, has been subject to debate. Like McLintock [3], Du et al [5], Zhang et al [6], and Gülder and Baksh [7] also suggested that the chemical effect of CO 2 is to prompt gas phase soot precursor oxidation by enhancing OH radical concentrations. Based on their experimental measurements of soot volume fraction distributions along the flame centerline of diluted acetylene coflow diffusion flames, Angrill et al [8] concluded that addition of CO 2 to the oxidizer side reduced soot formation but did not affect soot oxidation close to the visible flame tip.…”

“…There have been several studies to investigate the influence of CO 2 dilution effects on soot formation in both counterflow and coflow diffusion flames at atmospheric pressure over the last five decades [3][4][5][6][7][8][9][10][11][12]. When a diluent is introduced to either the fuel side or the oxidizer side of a diffusion flame it influences the flame properties and pollutant formation through the following three mechanisms [5]: dilution, thermal, and chemical.…”

“…However, Schug et al concluded that the effect of CO 2 addition on soot formation suppression is purely thermal [4]. The experimental studies of Du et al [5] and Gülder and Baksh [7], and to some extent the work of Zhang et al [6], provided convincing evidence that CO 2 suppresses soot formation not only through dilution and thermal effects, but also through chemical effects. The nature of the chemical effects of CO 2 on soot formation suppression, however, has been subject to debate.…”

Comparative study of the influence of CO2 and H2O on the chemical structure of lean and rich methane-air flames at atmospheric pressure

“…The chemical effect of CO 2 on the burning velocity of hydrocarbon-air flames was generally attributed to an increase in the rate of the reaction CO 2 + H = CO + OH [20][21][22]. This reaction consumes H atoms and reduces the rate of the main branching reaction H + O 2 = OH + O.…”