Soot Particle Nucleation Research Articles

Evolution of char chemistry, crystallinity, and ultrafine structure during pulverized-coal combustion

Detailed modeling of soot particle nucleation, growth and oxidation in laminar premixed ethylene-air flames at a pressure of 10 bar is presented. The employed kinetic model of soot formation, developed and tested earlier for subatmospheric and atmospheric flames, can quantitatively describe the experimental soot volume fraction profiles collected in a number of ehtylene flames at high pressures. The kinetic model consists of initial aromatic ring formation from nonaromatic species, planar polycyclic aromatic hydrocarbon (PAH) growth through the hydrogen-abstraction-acetylene-addition reaction mechanism, particle nucleation through coalescence of PAHs, particle growth by coagulation and surface reactions of the forming clusters and particles, and particle oxidation. Analysis of the computational results obtained at 10 bar and additional tests performed for a 1-bar flame suggest that the influence of pressure on soot production arises mainly from the larger concentration of acetylene, which affects both the soot surface growth and the nucleation of soot particles.

Detailed modeling of soot formation in laminar premixed ethylene flames at a pressure of 10 bar

Detailed modeling of soot particle nucleation, growth and oxidation in laminar premixed ethylene-air flames at a pressure of 10 bar is presented. The employed kinetic model of soot formation, developed and tested earlier for subatmospheric and atmospheric flames, can quantitatively describe the experimental soot volume fraction profiles collected in a number of ehtylene flames at high pressures. The kinetic model consists of initial aromatic ring formation from nonaromatic species, planar polycyclic aromatic hydrocarbon (PAH) growth through the hydrogen-abstraction-acetylene-addition reaction mechanism, particle nucleation through coalescence of PAHs, particle growth by coagulation and surface reactions of the forming clusters and particles, and particle oxidation. Analysis of the computational results obtained at 10 bar and additional tests performed for a 1-bar flame suggest that the influence of pressure on soot production arises mainly from the larger concentration of acetylene, which affects both the soot surface growth and the nucleation of soot particles.

A computational study of sooting limits in laminar premixed flames of ethane, ethylene, and acetylene

The onset of sooting in laminar premixed flames was examined computationally. Three series of atmospheric fueloxygennitrogen flames of ethane, ethylene, and acetylene were simulated using a detailed chemical kinetic model of soot particle nucleation and growth. It was found that the critical equivalence ratios for soot appearance, both the absolute values and temperature dependencies, can be predicted fairly close to the experimental observations, even when no reactions for the oxidation of aromatics by hydroxyl are included in the mechanism. The analysis of the computational results strongly suggests that the appearance of soot is controlled by two factors, concentration of acetylene and growth of polycyclic aromatics, and the latter is limited by the rise in flame temperature towards the end of the main reaction zone. The present results and conclusions are in agreement with the principal findings of previous modeling studies.

Detailed modeling of soot particle nucleation and growth

Detailed modeling of soot particle nucleation and growth in laminar premixed hydrocarbon flames is presented. The model begins with fuel pyrolysis, followed by the formation of polycyclic aromatic hydrocarbons, their planar growth and coagulation into spherical particles, and finally, surface growth and oxidation of the particles. The computational results are in quantitative agreement with experimental results from several laminar premixed hydrocarbon flames. A detailed analysis of soot particle inception and surface growth processes is presented. Surface growth was described in terms of elementary chemical reactions of surface active sites. The density of these sites was found to depend on the chemical environment. The model predicts the classical picture of soot particle inception and the classical description of soot particle structure.

Initial stages of soot formation in thermal pyrolysis of acetylene. II. A model for the incipience and growth of soot particles

A model is developed which describes simultaneously occurring processes of the initial hydrocarbon pyrolysis, nucleation, surface growth, and coagulation of soot particles. The model permits one to find the size distribution of the “primary” soot particles up to size 30–40 nm using a relatively small set of equations. The computed time dependence of soot particle concentration agrees satisfactorily with available experimental data. The existence of two limiting stages of the soot formation is revealed.

Concentration and mass distribution of charged species in sooting flames

Total concentration and mass distribution of charged species larger than about 300 amu were measured along the centerline of a premixed sooting acetylene/oxygen flat flame at 20 mmHg. Charge concentration was determined by measuring the electric current delivered to a Faraday cage in the detection chamber of a staged molecular beam flame sampling instrument having a quenching time of about 1 μs. Charge/mass ratio distributions were measured by the incremental electrical filtration of charged species from the beam. Mass and diameter distributions were than calculated by assuming unicharged species of density 2 g/cm 3 . The observed species, which include heavy hydrocarbon ions and charged soot particles, are of positive polarity. Their total concentration at fuel equivalence ratios in the range 2.1–3.0 and cold gas velocities of 31 and 38 cm/s ranges from 10 8 to 10 12 cm −3 , exhibits a distinct peak near the onset of soot formation, increases strongly with increasing fuel equivalence ratio, and decreases with increasing cold gas velocity. The mass distribution of charged species peaks sharply at a mass which increases with increasing height above the burner or time. At a fuel equivalence ratio of 2.25 and a cold gas velocity of 31 cm/s, the peak mass and its equivalent diameter increase from 1390 amu and 13just prior to the onset of visible soot formation to 7700 amu and 23about 2 ms later. The concentration of heavy hydrocarbon ions and that of heavy hydrocarbon molecules estimated previously decrease rapidly with the onset of soot formation in a manner that correlates with the initially fast surface gorwth of soot particles. Thus the heavy hydrocarbons appear to include both soot nuclei and surface growth intermediates. The concentrations of heavy hydrocarbon ions are much larger than the peak concentrations of soot particles. Therefore ionic nucleation of soot particles is feasible for these conditions, and a tentative mechanism is described.