A large-eddy-simulation study of soot formation in n-dodecane and biodiesel spray flames

Combustion and soot formation in a turbulent diffusion flame are simulated. Chemistry of combustion is treated with a detailed reaction mechanism that employs 49 species and 277 reactions. Turbulence is taken into account via the corrected k–ε model. Radiation heat transfer from flame is modelled by the P-1 model. An empirical model proposed by Khan and Greeves and two semi-empirical models proposed by Tesner and Lindstedt are used to simulate the soot formation in the flame. Khan and Greeves model showed to underpredict the maximum soot volume fraction. Nevertheless, the main shortcoming of Khan and Greeves model which undermines the applicability of this model to prediction of soot formation in turbulent diffusion flames is the inability to locate the highly sooting regions of the flame properly. Tesner model underpredicts the soot formation significantly, although the predicted shapes of the soot profiles are in accordance with the experimental measurements. Lindstedt model performs well in predicting both the maximum soot formation and the soot profile shapes in the chamber. Therefore, Lindstedt model can be considered as the most suitable model for the prediction of soot formation in turbulent diffusion flames.

This research work studied the effects of oxidant constitution on soot formation in diffusion flames by simultaneously measuring the soot properties and the species concentration. The soot properties are measured by the laser light scattering and extinction method and the hydroxyl concentration is measured by the laser-saturated fluorescence (LSF) method. The temperature distributions in the flames were measured by the two-line LSF technique and by fine wire thermocouple. . The hydroxyl fluorescence profiles for all four flames presented here show that the OH fluorescence intensities peak near the flame front. The OH fluorescence intensity drops sharply towards the dark region of the flame and continues declining to the sooting region. The OH fluorescence profiles also indicate that OH fluorescence decreases with increasing height in the flames for all flames investigated. Varying the oxidizer composition resulted in corresponding variation in the maximum OH concentration and flame temperature. Furthermore, it appears that the maximum OH concentration for each flame increases with increasing flame temperature. Soot particles are formed on the fuel side of the flame front where the number density is high for all four flames. The fuel/oxygen/argon flame (Flame C) shows the largest soot particle size, and shortest flame height. In the higher portion of the Flame C, the soot volume fraction was observed to decrease indicating that soot is being oxidized before leave the flame. The fuel/oxygen/carbon dioxide flame (Flame B) shows the least soot formation in the flame. The experiment demonstrated that soot formation can be reduced by changing the inert of the oxidant while keeping the fuel flow rate and oxygen flow rate constant. The carbon dioxide dramatically reduced the soot formation in the flames. The temperature effect may play the major role in this reduction. Some researchers have doubted that the hydroxyl radical is the dominant oxidizer of the soot particles in flames. In this investigation, both calculation and measurement data show that the highest OH concentration flame has the most soot formation inside the flame.

Effects of ammonia addition on soot formation in ethylene laminar diffusion flames. Part 2. Further insights into soot inception, growth and oxidation

Study of soot formations in co-flow laminar diffusion flames of n-heptane and oxygenated aromatic biofuels from atmospheric condition to 2.3 bar

Effects are investigated of constant and alternating electric and of magnetic fields on the soot formation in plane diffusional acetylene—and benzene—oxygen low-pressure counterflow flames. When electric fields are applied to the flame, reduction in the soot outflow and formation in the flame of dense aggregates shaped like laminae and droplets were observed. It was shown that the soot aggregates possess a skeleton. Alternating electric fields imposed on the flame inhibit skeleton formation and move the aggregate formation process to the later stages of soot aerosol formation, which leads to the production of dense aggregates and reduces the soot outflow. It is concluded that the observed smallest carbon particles (below 1 nm) are the basic structural soot units. In flames permeated by a magnetic field, the structural soot units form chains, from which domains are formed.

The effect of small additions of oxygen to the fuel on formation of soot in methane-air diffusion flames was studied over a range of flow rates and of burner diameters. The flames studied were shorter than those of previous studies, purely blue or blue and yellow without soot escape. Heights of various distinctive features were measured, and composition and temperature profiles were obtained; the distinctive features include.onset and termination of visible emission of radiation and deposition of material on a quartz filament inserted into the flame. The results indicate negligible influences of oxygen addition and thereby suggest that ions from the primary mechanism CH+Orarr;CHO++e- are unimportant in soot formation in these flames. A simplified one-step kinetic model accounting for buoyancy and momentum was developed and employed to obtain estimates of overall rate parameters for flame attributes related to soot formation.

Experimental characterization of the different nitrogen dilution effects on soot formation in ethylene diffusion flames

The large potential importance of diesel engines and of synthetic fuels has led to a surge of interest in the associated problem ofsoot formation. It is well known1 that the formation of soot and polycyclic aromatic hydrocarbons (PAH) is strongly influenced by fuel type. Studies in gas turbine-type combustors2–4 and simple laboratory systems such as laminar diffusion flames5–9, premixed flames10–11 and well-stirred reactors2–13, have shown that aromatic fuels have a high propensity to form soot. Recent studies of soot formation in premixed flames using light scattering techniques14–15 have demonstrated the application of the laws of physical coagulation to the later stages of soot formation in flames of different fuels. These studies show that the important difference between fuels,and hence more generally a dominant factor in soot formation, is the mass of carbonaceous material that enters this coagulating system. Thus, it is important to understand the early stages of the chemistry of the fuel oxidation and pyrolysis, the pre-particle chemistry. Since previous studies suggest that the intact aromatic ring, not fragments thereof, is largely responsible for the marked propensity of aromatics to form soot16–19, a detailed study of the preservation or destruction of the ring in rich flames of benzene seems worthwhile.

Ionization and soot formation in premixed flames

Modeling soot formation in flames and reactors: Recent progress and current challenges

Soot formation characteristics of well-defined spray flames

This project is concerned with the kinetics and mechanisms of aromatics oxidation and the growth process to polycyclic aromatic hydrocarbons (PAH) of increasing size, soot and fullerenes formation in flames. The overall objective of the experimental aromatics oxidation work is to extend the set of available data by measuring concentration profiles for decomposition intermediates such as phenyl, cyclopentadienyl, phenoxy or indenyl radicals which could not be measured with molecular-beam mass spectrometry to permit further refinement and testing of benzene oxidation mechanisms. The focus includes PAH radicals which are thought to play a major role in the soot formation process while their concentrations are in many cases too low to permit measurement with conventional mass spectrometry. The radical species measurements are used in critical testing and improvement of a kinetic model describing benzene oxidation and PAH growth. Thermodynamic property data of selected species are determined computationally, for instance using density functional theory (DFT). Potential energy surfaces are explored in order to identify additional reaction pathways. The ultimate goal is to understand the conversion of high molecular weight compounds to nascent soot particles, to assess the roles of planar and curved PAH and relationships between soot and fullerenes formation. The specific aims are to characterize both the high molecular weight compounds involved in the nucleation of soot particles and the structure of soot including internal nanoscale features indicative of contributions of planar and/or curved PAH to particle inception.

Effects of ambient pressure and precursors on soot formation in spray flames

Effects of fuel droplet size on soot formation in spray flames formed in a laminar counterflow

Effects of H2 addition on soot formation in counterflow diffusion flames of propane: A comparative analysis with He and N2 addition