Soot Surface Oxidation Research Articles

Tracing the plasma kallikrein-kinin system-activating component in the atmospheric particulate matter with different origins

Atmospheric particulate matter (PM) perturbs hematological homeostasis by targeting the plasma kallikrein-kinin system (KKS), causing a cascade of zymogen activation events. However, the causative components involved in PM-induced hematological effects are largely unknown. Herein, the standard reference materials (SRMs) of atmospheric PM, including emissions from the diesel (2975), urban (1648a), and bituminous coal (2693), were screened for their effects on plasma KKS activation, and the effective constituent contributing to PM-induced KKS activation was further explored by fraction isolation and chemical analysis. The effects of three SRMs on KKS activation followed the order of 2975 > 1648a > 2693, wherein the fractions of 2975 isolated by acetone and water, together with the insoluble particulate residues, exerted significant perturbations in the hematological homeostasis. The soot contents in the SRMs and corresponding isolated fractions matched well with their hematological effects, and the KKS activation could be dependent on the soot surface oxidation degree. This study, for the first time, uncovered the soot content in atmospheric PM with different origins contributed to the distinct effects on plasma KKS activation. The finding would be of utmost importance for the health risk assessment on inhaled airborne fine PM, given its inevitable contact with human circulatory system.

The impact of ammonia addition on soot formation in ethylene flames

The present work investigates computationally the impact of blending ammonia with ethylene on soot formation in four laminar diffusion flames and the corresponding turbulent partially premixed flames. The conditions conform to experimental investigations (Bennett et al., Combust. Flame, 2020, and Boyette et al., Combust. Flame, 2021) with both sets of flames featuring identical fuel blends. A mass and number density preserving sectional method was applied to all cases with the soot surface growth and oxidation models updated to include reactions with oxides of nitrogen. The gas phase chemistry was extended to include a comprehensively validated ammonia sub-mechanism. For the laminar flames, the inception of soot particles is based on detailed chemistry with pyrene treated as representative of the PAH pool. The accuracy of fitting a global acetylene-based inception step is evaluated for the different fuel blends and subsequently applied to the turbulent flames using a fully coupled transported joint probability density function method featuring an 84-dimensional joint-scalar space. Results obtained for laminar flames show that detailed chemistry coupled with the sectional soot model provides excellent agreement with the measured suppression of the soot volume fraction with increased use of ammonia. Computed particle size distributions (PSDs) show an increase in smaller soot particles under such conditions, consistent with experimental observations. The experimentally observed reduced impact in turbulent flames is also reproduced computationally. The suppression of soot is principally caused by changes in the radical pool leading to reduced soot surface growth and, to a lesser extent, soot inception. The contribution of oxides of nitrogen to soot oxidation is modest. Computed PSDs in laminar and turbulent flames highlight the importance of differences in flame structures and flowfield timescales.

Thermodynamics second-law analysis of hydrocarbon diffusion flames: Effects of soot and temperature

In this paper, a computation of the ethylene co-flow diffusion flame is carried out using the Co-flame code with a detailed gas-phase mechanism and soot model. A numerical analysis based on the thermodynamics second-law was conducted for developing a high-efficiency combustion condition of hydrocarbon diffusion flames. The entropy generations and exergy loss ratios due to thermal radiation, heat conduction and convection, and chemical reactions are numerically calculated, in which entropy generations caused by both gasses and soot particle are considered. The effects of soot (controlled by changing stoichiometric mixture fraction Zst from 0.1 to 0.62) and adiabatic flame temperature Tad (2300 K, 2500 K, 2700 K) on entropy generation and exergy loss ratio in flame are investigated. The results suggest that, entropy generation due to soot radiation and soot surface growth and oxidation accounts for about 15% and 5% in total radiation entropy generation and total chemical entropy generation, respectively. Entropy generation due to thermal radiation decreases when soot reduces, and entropy generation due to heat conduction and convection, mass diffusion and chemical reactions increases when Zst increases. When Tad is 2300 K, the change of exergy loss ratio is slight with a reducing of soot and increasing of Zst. When Tad is 2500 K and 2700 K, the exergy loss ratio has tendency of increasing with a reducing of soot and increasing of Zst. The exergy loss ratio increases with increasing of Tad.

Coupling LES with soot model for the study of soot volume fraction in a turbulent diffusion jet flames at various Reynolds number configurations

PurposeThis study aims to investigate the insights of soot formation such as rate of soot coagulation, rate of soot nucleation, rate of soot surface growth and soot surface oxidation in ethylene/hydrogen/nitrogen diffusion jet flame at standard atmospheric conditions, which is very challenging to capture even with highly sophisticated measuring systems such as Laser Induced Incandescence and Planar laser-induced fluorescence. The study also aims to investigate the volume of soot in the flame using soot volume fraction and to understand the global correlation effect in the formation of soot in ethylene/hydrogen/nitrogen diffusion jet flame.Design/methodology/approachA large eddy simulation (LES) was performed using box filtered subgrid-scale tensor. A filtered and residual component of the governing equations such as continuity, momentum, energy and species are resolved and modeled, respectively. All the filtered and residual components are numerically solved using the ILU method by considering PISO pressure–velocity solver. All the hyperbolic flux uses the QUICK algorithm, and an elliptic flux uses SOU to evaluate face values. In all the cases, Courant–Friedrichs–Lewy (CFL) conditions are maintained unity.FindingsThe findings are as follows: soot volume fraction (SVF) as a function of a flame-normalized length for three different Reynolds number configurations (Re = 15,000, Re = 8,000 and Re = 5,000) using LES; soot gas phase and particulate phase insights such as rate of soot nucleation, rate of soot coagulation, rate of soot surface growth and soot surface oxidation for three different Reynolds number configurations (Re = 15,000, Re = 8,000 and Re = 5,000); and soot global correction using total soot volume in the flame volume as a function of Reynolds number and Froude number.Originality/valueThe originality of this study includes the following: coupling LES turbulent model with chemical equilibrium diffusion combustion conjunction with semi-empirical Brookes Moss Hall (BMH) soot model by choosing C6H6 as a soot precursor kinetic pathway; insights of soot formations such as rate of soot nucleation, soot coagulation rate, soot surface growth rate and soot oxidation rate for ethylene/hydrogen/nitrogen co-flow flame; and SVF and its insights study for three inlet fuel port configurations having the three different Reynolds number (Re = 15,000, Re = 8,000 and Re = 5,000).

Properties and oxidation of in-cylinder soot associated with exhaust gas recirculation (EGR) in diesel engines

The properties and oxidation of in-cylinder soot from a diesel engine fueled with n-heptane were explored under the simulated exhaust gas recirculation (EGR) condition, via CO2 addition to the intake air of the engine. A self-developed total cylinder sampling system was employed to obtain the soot samples at the EGR ratios of 0 and 25%, and this study only focused on the soot oxidation that occurred in the soot oxidation-dominated (SOD) phase. Computational fluid dynamics (CFD) simulations were performed to determine the local combustion characteristics related to soot oxidation. Soot oxidation rates were evaluated based on in-cylinder soot mass traces and CFD results. Soot properties were characterized in terms of nanostructure, carbon chemical state, and surface functional groups. Detailed analysis of the soot mass indicates that EGR addition enhances the mass-based specific rate of soot oxidation. However, CFD results show that EGR addition reduces the flame temperature and the concentrations of O2 and OH, and consequently decreases soot surface oxidation rates by O2 and by OH. The characterization of soot properties shows that EGR decreases the degree of structural ordering and results in the formation of more oxygenated and aliphatic C–H groups on the soot surface. This alteration in physico-chemical properties favors soot oxidation during the combustion process, and results in an increase in the mass-based specific rate of soot oxidation in the SOD phase.

Effects of pressure on soot formation in laminar coflow methane/air diffusion flames doped with n-heptane and toluene between 2 and 8 atm

There is currently a lack of adequate understanding of soot formation in flames fueled with liquid hydrocarbons at elevated pressures. In this study, laminar coflow n-heptane and toluene doped CH4/air diffusion flames were numerically investigated under a constant carbon mass flow rate at pressures between 2 and 8 atm to understand how pressure affects the sooting propensity of these two main components of surrogate fuels mimicking gasoline. Numerical simulations were performed using a detailed reaction mechanism containing 175 species and 1175 reactions and a sectional soot model. Soot inception is modeled by collisions among pyrene, BAPYR and BGHIF. Soot surface growth and oxidation are modeled using the hydrogen abstraction acetylene addition (HACA) mechanism as well as PAH surface condensation. The predicted sensitivity of soot production to pressure is in better agreement with the measurements of Daca and Gülder (2017) when the soot aging effect is considered in HACA surface growth. The predicted soot concentrations are in overall good agreement with measurements. Propargyl recombination and propargyl reaction with propyne are important pathways for the formation of benzene. In methane+toluene flames, attack of toluene by H radical is an effective benzene formation pathway low in the flame, but the relative importance of benzene formation from toluene is reduced with increasing pressure. Although all the soot formation processes are enhanced with increasing pressure, PAH condensation is enhanced the most, followed by HACA and inception. At 6 and 8 atm, PAH condensation becomes comparable to HACA. The pressure dependence of the sooting propensity follows the order of methane+toluene < methane+n-heptane < methane, consistent with measurements. This result can be explained by the pressure dependence of benzene formation pathways, the kinetic effect of pressure, and the scrubbing effect of soot production on the gas-phase species involved in soot formation.

DNS-driven analysis of the Flamelet/Progress Variable model assumptions on soot inception, growth, and oxidation in turbulent flames

Modeling suites for Large-Eddy Simulations of soot evolution in turbulent flames include a number of submodels describing the chemistry of soot precursors, particle dynamics, heterogeneous soot chemistry, turbulent mixing, and combustion. To understand the reasons for model failure and to enhance the overall model performance, it is necessary to identify and subsequently improve model components with a leading order effect on the overall error. In this work, errors in soot predictions associated with flamelet-based combustion models are isolated and quantified in a combined a-priori and partial a-posteriori analysis using large-scale Direct Numerical Simulation (DNS) data of a sooting turbulent jet diffusion flame. Gas-phase quantities entering the calculation of the soot source terms and hence coupling the combustion model to the soot model are analyzed in the DNS first. The performance of a Flamelet/Progress Variable model with respect to these quantities is then analyzed a-priori for two DNS cases employing a mixture-averaged transport model and unity Lewis numbers. Then, the soot evolution along Lagrangian trajectories extracted from the DNS is re-computed using rate coefficients directly taken from the DNS and from the flamelet table. In the context of this partial a-posteriori analysis, flamelet-induced errors are also compared to errors induced by the chemical soot model. The soot surface growth and oxidation rate coefficients are reasonably well predicted by the flamelet library. Considerably larger errors in the model-predicted soot mass originate from the tabulated quantities entering the calculation of PAH-based soot growth rates. However, these errors can be reduced to a few percent if the rate is appropriately scaled with the mass fraction of polycyclic aromatic hydrocarbons (PAH). However, this requires the solution of a transport equation for the PAH mass fraction, and modeling the source term in this equation is shown to be challenging. Overall, the largest uncertainties can be attributed to the chemical mechanism for PAH formation and the model for the PAH source term.

Evaluation of a Lagrangian Soot Tracking Method for the prediction of primary soot particle size under engine-like conditions

This paper reports the implementation and evaluation of a Lagrangian soot tracking (LST) method for the modeling of soot in diesel engines. The LST model employed here has the tracking capability of a Lagrangian method and the ability to predict primary soot particle sizing. The Moss-Brookes soot model is used here as the Eulerian method to simulate soot formation and oxidation processes. The inception, surface growth and oxidation models are adopted and modified such that the associated reaction rates can be computed using the Lagrangian approach. The soot nuclei are treated as Lagrangian particles when the mass of incipient soot exceeds a designated threshold value. Their trajectories are then computed using the particle momentum equation. The change of primary soot particle size is dependent on the modified Lagrangian surface growth and soot oxidation models. Performance of the LST model in predicting temporal soot cloud development, mean soot diameter and primary soot size distribution is evaluated using measurements of n-heptane and n-dodecane spray combustion obtained under diesel engine-like conditions. In addition, sensitivity studies are carried out to investigate the influence of soot surface ageing and oxidation rates on the primary soot particle size distribution. With the use of surface ageing, the predicted maximum primary soot particle sizes are closer to the experimentally measured maximum primary soot sizes. Also, the associated particle size distribution shows a lognormal shape. A higher rate of soot oxidation due to OH causes the soot particles to be fully oxidized downstream of the flame. In general, the LST model performs better than the Eulerian method in terms of predicting soot sizing and accessing information of individual soot particles, both of which are shortcomings of the Eulerian method.

A numerical study on the effects of boot injection rate-shapes on the combustion and emissions of a kerosene-diesel fueled direct injection compression ignition engine

In this work, the effects of boot injection rate-shapes on the combustion process and emissions formation of a direct injection compression ignition engine fueled with kerosene and diesel are investigated through numerical simulations. Boot injection rate-shapes with varying boot injection velocity and boot injection duration are used. The KIVA4-CHEMKIN code is used in conjunction with a phenomenological soot model and an improved kerosene-diesel reaction mechanism to study the combustion process and emissions formation. The phenomenological soot model consists of a number of sub-models from literature that accounts for soot particle inception, soot coagulation, soot surface growth via the hydrogen-abstraction-carbon-addition (HACA) mechanism and soot surface oxidation by oxygen (O2) and hydroxyl radical (OH). It should be noted that the improved kerosene-diesel reaction mechanism is robust enough to predict the combustion and emissions trends of kerosene with respect to diesel. From this study, boot injection rate-shapes are seen to cause combustion phasing and cause lower nitrogen oxide (NO) emissions in general. Furthermore, it is observed that when kerosene replaces diesel, engine efficiency and NO emissions increase while carbon monoxide (CO) and soot emissions decrease. Soot mass quantity, soot particle number and soot particle size are the lowest for pure kerosene combustion. Finally, detailed analyses of the effects of boot injection rate-shapes on soot particle dynamics are also presented.

Numerical modelling of soot formation and oxidation using phenomenological soot modelling approach in a dual-fueled compression ignition engine

Modelling soot formation and oxidation in diesel engines has been a long-standing challenge. In this study, soot particle characteristics in terms of particle dynamics, particle size and number density were modelled by integrating a multi-step phenomenological soot model into the KIVA-CHEMKIN CFD code for compression ignition engine combustion simulations. This semi-detailed soot model is dedicated to solving rate equations using sub-models to account for precursor formation, soot particle inception and coagulation as well as soot surface growth and oxidation. Soot growth and oxidation is inherently derived from the concentration of certain species found in the chemical reaction mechanism used, namely H, O2, C2H2 and the nucleating polycyclic aromatic hydrocarbon (PAH). Acetylene is taken as the core precursor species in nucleating PAH, soot inception as well as acetylene-assisted soot surface growth. The integrated multi-step phenomenological soot model has been validated under gasoline and diesel dual-fuel engine conditions.The predicted histograms of soot particle number along with size distribution contribute towards the understanding of dominant factors that affect soot formation. The factors affecting soot particle under varying engine loads and fuel conditions were extensively investigated. Generally, the predicted soot particle size was larger for heavy-sooting conditions as compared to low-sooting conditions. For port-injected gasoline-dominated combustion, there is less soot being discharged. This might be attributed to two reasons. First, a more homogenous mixture is realized with less diesel fuel, thus effectively reducing the formation of soot precursors. The other reason is the intensive heat release which enhances the depletion of soot precursors, thereby impeding the growth of soot particles in terms of size and mass.

Sensitivity study of engine soot forming using detailed soot modelling oriented in soot surface growth dynamic

Development of detailed soot model independent of empirical expression is supposed to reasonably replicate the soot formation and oxidation dynamic kinetics over a wide range of diesel engine operations, thus facilitates exploring crucial factor of soot forming. Based on comprehending of varying mixture inhomogeneity on soot forming under engine operations, a new multi-step soot model oriented in surface growth dynamic had so far been updated in this study. By correlation analysis, the new soot model is able to display the influence of both temperature and mixture inhomogeneity on soot surface activity by revising the parameter of the fraction of active sites. Hence the dominant factor of soot forming is conducted by sensitivity study in aspect of three distinctive phases: fast soot inception, soot growth equilibrium and soot oxidation prevailing, under varying mixture inhomogeneity. The soot inception is more influenced by temperature under uniform mixture combustion, but the dominant factor is switched to mixture inhomogeneity in stratified mixture wherein the acetylene formation rate gets the maximum. Similarly, less oxygen helps soot abatement due to weaker chemistry reactive in soot surface growth caused by lower temperature in homogenous mixture. Nevertheless, stimulated soot surface growth by activated surface activity and vast precursor deposit under heterogeneous mixture conduces to soot forming. Simultaneously, impaired soot surface oxidation under nonuniform mixture accelerates the deteriorated engine-out soot in comparison with discharged soot in less homogenous mixture.

Soot Particle Evolution and Transport in a Direct Injection Diesel Engine

Particle-based in-cylinder soot distribution study is becoming more important as the rules and regulations pertaining to particulate emission of diesel-powered vehicles have been increasingly more stringent. This paper focuses on the investigation of soot size evolution and its distribution and transport inside an engine cylinder. The overall process of soot formation includes soot nucleation, surface growth, oxidation, coagulation and agglomeration. The present study considers only soot surface growth, oxidation and coagulation to predict the in-cylinder soot particle size. The soot surface growth model was based on Hiroyasu’s soot formation model while soot oxidation was referred to Nagle &amp; Strickland-Constable’s soot oxidation model. Coagulation rate was defined using Smoluchowski’s equation with constant proposed by Wersborg. From this study, it is demonstrated that soot particles with relatively larger size are gathered in the centre of the cylinder while smaller soot particles are found to be in the region near the wall. Soot number density is considerably high at the start of combustion and reduces sharply afterward while the soot particle size shows the opposite trend. Soot formation rate was found to be dominant at earlier crank angle and is overcome by soot oxidation and coagulation processes that caused lower soot number density but higher soot particle size.

Modeling DME Addition Effects to Fuel on PAH and Soot in Laminar Coflow Ethylene/Air Diffusion Flames Using Two PAH Mechanisms

Effects of dimethyl ether (DME) addition to fuel on polycyclic aromatic hydrocarbons (PAH) and soot formation in laminar coflow ethylene/air diffusion flames were revisited numerically. Calculations were conducted using two gas-phase reaction mechanisms with PAH formation and growth: one is the C2 chemistry of the Appel, Bockhorn, and Frenklach (ABF) mechanism with PAH growth up to A4 (pyrene); the other is also a C2 chemistrymechanism newly developed at the German Space Center (DLR) with PAH growth up to A5 (corannulene). Soot was modeled based on the assumptions that soot inception is due to the collision of two pyrene molecules, and soot surface growth and oxidation follow a hydrogen abstraction carbon addition (HACA) sequence. The DLR mechanism predicted much higher concentrations of pyrene than the ABF mechanism. A much smaller value of α in the surface growth model associated with the DLR mechanism must be used to predict the correct peak soot volume fraction. Both reaction mechanisms are capable of predicting the synergistic effect of DME addition to fuel on PAH formation. The locations of high PAH concentrations predicted by the DLR mechanism are in much better agreement with available experimental observations. A weak synergistic effect of DME addition on soot formation was predicted by the ABF mechanism. The DLR mechanism failed to predict the synergistic effect on soot. The likely causes for such a failure and the implications for future research on soot inception and surface growth were discussed.

On the effect of carbon monoxide addition on soot formation in a laminar ethylene/air coflow diffusion flame

The effect of carbon monoxide addition on soot formation in an ethylene/air diffusion flame is investigated by experiment and detailed numerical simulation. The paper focuses on the chemical effect of carbon monoxide addition by comparing the results of carbon monoxide and nitrogen diluted flames. Both experiment and simulation show that although overall the addition of carbon monoxide monotonically reduces the formation of soot, the chemical effect promotes the formation of soot in an ethylene/air diffusion flame. The further analysis of the details of the numerical result suggests that the chemical effect of carbon monoxide addition may be caused by the modifications to the flame temperature, soot surface growth and oxidation reactions. Flame temperature increases relative to a nitrogen diluted flame, which results in a higher surface growth rate, when carbon monoxide is added. Furthermore, the addition of carbon monoxide increases the concentration of H radical owing to the intensified forward rate of the reaction CO + OH = CO 2 + H and therefore increases the surface growth reaction rates. The addition of carbon monoxide also slows the oxidation rate of soot because the same reaction CO + OH = CO 2 + H results in a lower concentration of OH.

Soot surface growth and oxidation at pressures up to 8.0 atm in laminar nonpremixed and partially premixed flames

The flame structure and soot particle surface reaction properties, including growth and oxidation, of laminar jet nonpremixed flames were studied experimentally at pressures of 1.0–8.0 atm. Ethylene–helium mixtures were used in an oxygen/helium coflow at normal temperature (300 K) in order to minimize the effects of buoyancy. The following properties along the axis of flames were measured as a function of distance from the burner exit: soot concentrations by laser extinction, soot temperatures by multiline emission, soot structure by thermophoretic sampling and analysis using transmission electron microscopy (TEM), concentrations of major stable gas species by isokinetic sampling and gas chromatography, concentrations of radical species (H, OH, O) by Li/LiOH atomic absorption, and flow velocities by laser velocimetry. The measurements were analyzed to determine local flame properties in order to find soot surface growth and oxidation rates. The measurements of soot surface growth rates (corrected for soot surface oxidation) were found to be consistent with earlier measurements at atmospheric and subatmospheric pressures involving laminar premixed and diffusion flames fueled with a variety of hydrocarbons. The growth rates from all the available flames were in good agreement with each other and with existing hydrogen-abstraction/carbon-addition (HACA) soot surface growth mechanisms available in the literature. Measurements of early soot surface oxidation rates at pressures of 1.0–8.0 atm (corrected for soot surface growth and prior to consumption of 70% of the maximum mass of the primary soot particles) were found to be consistent with earlier measurements at atmospheric and subatmospheric pressures. The oxidation rates of up to 8 atm in flame environment could be explained by reaction with OH, having a collision efficiency of 0.12.

Detailed soot field in a turbulent non-premixed ethylene/air flame from laser scattering and extinction experiments

A soot-containing turbulent non-premixed flame burning ethylene in atmospheric-pressure air was investigated by conducting nonintrusive laser scattering and extinction experiments at various axial and radial flame locations. Mean soot properties of principal interest—soot volume fraction, spherule (primary particle) diameter, and aggregate size and fractal dimension—were characterized based on the Rayleigh–Debye–Gans scattering theory, which can properly account for the actual particulate size and morphology. In situ evidence for the formation of precursor particles and their carbonization to mature soot, as well as the onset of the aggregation process, was observed low in the flame. Maximum mean soot volume fraction and spherule diameter were about 1 ppm and 28 nm, respectively, both peaking at similar axial locations. The mean number of spherules per aggregate continuously increased along the flame centerline with the cluster–cluster aggregation mechanism leading to a fractal dimension of 1.8. Radial variations of mean soot field were also observed with the possible exception of the aggregate radius of gyration. Decoupling of spherule and aggregate sizes during the present analysis of optical measurements allowed the separation of soot surface growth, oxidation, and aggregation processes. Such accurate descriptions of soot dynamics in a lightly sooting turbulent flame are valuable in assessing computational soot models and other particulate diagnostics.

Size and Morphology of Soot Particulates Sampled from a Turbulent Nonpremixed Acetylene Flame

Soot processes within a turbulent nonpremixed flame burning acetylene/air were investigated by conducting thermophoretic sampling experiments at various axial and radial locations. Analyses of transmission electron microscope images yielded the mean soot spherule diameter, number of spherules per aggregate, and fractal morphology within this highly luminous turbulent flame. Specifically, translucent particles were observed at low-to-intermediate heights above the flame with the formation and evolution of young soot precursors. The soot spherule diameter peaked at 34 nm halfway along the centerline, identifying the flame regions of surface growth and oxidation processes. In the meantime, the aggregation was continuous along the flame axis with the mean number of spherules per aggregate reaching 150 at the highest sampling location. Size ranges of spherules and aggregates were narrow and broad, respectively, while the relative widths of both size distributions remained similar throughout the flame. In contrast to the observed axial variations, the radial changes of the mean spherule and aggregate sizes appeared to be small. Aggregate morphologies were universally characterized by a fractal dimension of 1.82 and a fractal prefactor of 1.9 for all the flame positions. In comparison to a lightly sooting ethylene flame, these measurements in the acetylene turbulent flame revealed that the fuel type mainly affected the axial evolution of spherule diameters but not their range, and enhanced the aggregate sizes but not their morphology. The effective decoupling of spherule and aggregate sizes permitted the separation of soot surface growth and oxidation from aggregation. This key aspect provided a stringent test for the existing particulate diagnostics and predictive models in their ability to quantify the actual particle surface area, particularly in optically thick conditions that are encountered in many practical combustion environments.

Soot Surface Reactions in High-Temperature Laminar Diffusion Flames

The structure and the soot surface growth and surface oxidation properties of round laminar jet diffusion flames were studied experimentally. Measurements were made along the axes of acetylene/argon-fueled flames burning at atmospheric pressure in coflowing oxygen/argon mixtures to provide higher temperature soot-containing regions (2000‐2350 K) than were considered during earlier work. The measurements yielded soot surface growth and surface oxidation rates as well as the flame properties that are thought to control these rates. The present measurements of soot surface growth rates (corrected for soot surface oxidation) were consistent with earlier measurements in laminar premixed and diffusion flames having lower temperatures and exhibited good agreement with existing hydrogen-abstraction/carbon-addition soot surface growth rate mechanisms in the literature with steric factors of these mechanisms having values on the order of unity, as anticipated. Similarly, the present measurements of soot surface oxidation rates (corrected for soot surface growth) were consistent with earlier measurements in laminar premixed and diffusion flames having lower temperatures and exhibited good agreement with existing OH soot surface oxidation mechanisms in the literature, with a collision efficiency for OH of 0.13, in good agreement with past work, and supplemented to only a minor degree by direct soot surface oxidation by O2.

Soot surface growth and oxidation in laminar diffusion flames at pressures of 0.1–1.0 atm

The flame and soot structure and the soot surface growth and oxidation properties of round laminar jet diffusion flames were studied experimentally at pressures of 0.1–1.0 atm. Measurements were made along the axes of flames fueled with acetylene–nitrogen mixtures and burning in coflowing air with the reactants at normal temperature (300 K). The following properties were measured as a function of distance from the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using Transmission Electron Microscopy (TEM), concentrations of major stable gas species (N2, Ar, H2O, H2, O2, CO, CO2, CH4, C2H2, C2H4, C2H6, C3H6, C3H8, and C6H6) by isokinetic sampling and gas chromatography, concentrations of some radial species (H, OH, O) by deconvoluted Li/LiOH atomic absorption, and flow velocities by laser velocimetry. These measurements yielded local soot surface growth and oxidation rates, as well as local flame properties that are thought to affect these rates. Present measurements of soot surface growth rates (corrected for soot surface oxidation) in laminar diffusion flames at various subatmospheric pressures were consistent with earlier measurements of soot surface growth rates in laminar premixed and diffusion flames involving a variety of hydrocarbons at atmospheric pressure; in addition, rates from all the available flames were in good agreement with each other and with existing Hydrogen-Abstraction/Carbon-Addition (HACA) soot surface growth mechanisms in the literature for values of steric factors in these mechanisms on the order of unity, as expected. Similarly, present measurements of early soot surface oxidation rates (corrected for soot surface growth and prior to consumption of 70% of the maximum mass of the primary soot particles) for fuel-rich and near-stoichiometric conditions in laminar diffusion flames at pressures of 0.1–1.0 atm were consistent with earlier measurements of rates of early soot surface oxidation in laminar premixed and diffusion flames involving a variety of hydrocarbons at atmospheric pressure; in addition, rates from all available flames could be explained by reaction with OH, as proposed by K.G. Neoh et al. (in: Particulate Carbon, Plenum, New York, 1980, p. 261), having a collision efficiency of 0.13 and supplemented to only a minor degree by direct soot surface oxidation by O2.

03/02039 Modeling and experimental study on an innovative passive cooling system-NVP system: Kang, Y. et al. Energy and Buildings, 2003, 35, (4), 417–425

The flame and soot structure and the soot surface growth and oxidation properties of round laminar jet diffusion flames were studied experimentally at pressures of 0.1–1.0 atm. Measurements were made along the axes of flames fueled with acetylene–nitrogen mixtures and burning in coflowing air with the reactants at normal temperature (300 K). The following properties were measured as a function of distance from the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using Transmission Electron Microscopy (TEM), concentrations of major stable gas species (N2, Ar, H2O, H2, O2, CO, CO2, CH4, C2H2, C2H4, C2H6, C3H6, C3H8, and C6H6) by isokinetic sampling and gas chromatography, concentrations of some radial species (H, OH, O) by deconvoluted Li/LiOH atomic absorption, and flow velocities by laser velocimetry. These measurements yielded local soot surface growth and oxidation rates, as well as local flame properties that are thought to affect these rates. Present measurements of soot surface growth rates (corrected for soot surface oxidation) in laminar diffusion flames at various subatmospheric pressures were consistent with earlier measurements of soot surface growth rates in laminar premixed and diffusion flames involving a variety of hydrocarbons at atmospheric pressure; in addition, rates from all the available flames were in good agreement with each other and with existing Hydrogen-Abstraction/Carbon-Addition (HACA) soot surface growth mechanisms in the literature for values of steric factors in these mechanisms on the order of unity, as expected. Similarly, present measurements of early soot surface oxidation rates (corrected for soot surface growth and prior to consumption of 70% of the maximum mass of the primary soot particles) for fuel-rich and near-stoichiometric conditions in laminar diffusion flames at pressures of 0.1–1.0 atm were consistent with earlier measurements of rates of early soot surface oxidation in laminar premixed and diffusion flames involving a variety of hydrocarbons at atmospheric pressure; in addition, rates from all available flames could be explained by reaction with OH, as proposed by K.G. Neoh et al. (in: Particulate Carbon, Plenum, New York, 1980, p. 261), having a collision efficiency of 0.13 and supplemented to only a minor degree by direct soot surface oxidation by O2.