Average Primary Particle Diameter Research Articles

Effects of Oxygen Concentration on Soot Formation in Ethylene and Ethane Fuel Laminar Diffusion Flames

In studying the effects of oxygen concentration and molecular structure on the morphologies of the soot particles produced by hydrocarbon fuels, ethylene and ethane were chosen as experimental fuels. With a Gülde laminar coaxial diffusion flame device, a soot particle device was used to sample soot particles at different oxygen concentrations (21%, 24%, 26%, 28%, and 31%) and at different heights above a burner (HABs = 10 mm, 20 mm, 30 mm, 40 mm, and 50 mm). High-resolution transmission electron microscopy (HRTEM) was used to scrutinize and analyze the soot particles at varying oxygen concentrations. The findings suggest that at the same oxygen concentration, ethylene produces brighter and taller flames. With an increase in the oxygen concentration, ethylene flames and ethane flames gradually decrease in height and become brighter. With an increase in the HAB, the average primary soot particle diameter (Dp) increases initially and then decreases, the fractal dimension (Df) increases, and the aggregates transition from strips and chains to clusters. At the same flame height (HAB = 30 mm), the Dp decreases, the Df increases, the carbon layer torsion resistance (Tf) and the carbon layer spacing (Ds) increase, and the carbon layer changes from a parallel arrangement to a curved arrangement to form denser network aggregations.

Evolution of collisional condensation of biodiesel combustion particulate matter in engine exhaust pipe

To investigate the evolution of biodiesel combustion particulate matter (PM) within the engine exhaust system, PM samples were analyzed from diesel fuel, soybean oil methyl ester (SME), catering waste oil methyl ester (WME) and palm oil methyl ester (PME) at various locations along the engine exhaust pipe, and a gas-solid two-phase flow model of exhaust gas and PM was developed using the coupled computational fluid dynamics-discrete element method (CFD-DEM). The results indicate that the average primary particle diameter of biodiesel PM is smaller than that of diesel PM at the same position within the exhaust pipe, and it exhibits an increasing trend with respect to the iodine value of biodiesel. The adhesion forces of diesel, SME, WME, and PME PM at 0 m downstream from the exhaust pipe were measured as 9.83 nN, 16.74 nN, 26.54 nN, and 34.31 nN, respectively. The biodiesel PM with higher mass density readily formed structurally stable particulate agglomerates at the inlet of the exhaust pipe. With an increase in exhaust flow velocity, there was a corresponding rise in particle collision frequency. The initial agglomeration probability of particles exhibited an increase followed by a subsequent decrease. The normal overlap of particle collisions decreased with an increase in the Young's modulus of the particles, thereby reducing the likelihood of adsorption and adhesion during particle collision and hindering the formation of a greater number of particle aggregates.

Part I: determination of a structure/property transformation mechanism responsible for changes in the point of zero change of anatase titania with decreasing particle size.

Below a diameter of approximately 28 nm, the surface crystal structure of anatase titania is known to change. These changes include surface bond lengths and crystal lattice parameter expansion/contractions. Concurrent with these structure changes, the materials point of zero charge (PZC) has been observed to shift toward lower pH values. Therefore, the objective of this work was to determine if a correlation exists between these known structural changes and the shift in the materials PZC values with decreasing particle size. To achieve this a method was developed to identify and minimize the effect of all known variables, save particle size, affecting the materials pHPZC. This led to the discovery of two regions for point of zero charge. Above the average spherical primary particle diameter ≅ 29 nm for anatase titania, denoted as Region I, PZC values remain constant. In Region I the materials surface crystal structure and properties were also found to remain constant. Below the average spherical primary particle diameter ≅29 nm is the second zone, defined as Region II, where pHPZC values decrease almost linearly. An examination of possible surface structure factors and properties responsible for the shift in these PZC values (Region II) identified three underlying causes. These being changes in the materials band gap (i.e. surface bond lengths), lattice parameters and bond ionic content.

Part II: superconductivity observed in magnetically separated nanoscale anatase titania at ambient temperature and pressure in an aqueous environment at its point of zero charge.

This is the first work to investigate if and/or how changes in the surface structure/properties affect the charge transfer resistance (R CT) of anatase titania with decreasing particle size. It was accomplished by measuring the R CT (Ω) of same weight anatase titania pellets, with particle sizes ranging from 5.31 nm to 142.61 nm. Measurements were made using Electrochemical Impedance Spectroscopy (EIS) at each material's point of zero charge (PZC). Results demonstrated two regions of R CT. Above an average primary particle diameter of 23.54 nm, R CT remained essentially constant. Below, this diameter the R CT value first increased significantly, then decreased almost linearly toward zero. The projected average primary particle diameter where the materials R CT was projected to reach zero resistance is at a diameter of approximately 4.39 nm. A simple test was then developed to determine if at a small enough particle size the material would be affected by an external magnetic field. It was found that a sample with an average particle diameter of 12.689 nm, formed fine needles/threads of particles in deionized water, perpendicular to the settled powder at the base of the potash tube. This led to the development of a simple magnetic separation method to obtain strongly diamagnetic material from a parent population with an average primary particle diameter of 5.31 nm. A pellet consisting of these magnetically separated particles was then pressed at the same weight and pressure as the prior samples. The pellet's R CT was then measured using EIS under the identical conditions as the prior samples. EIS results of the magnetically separated particles in pellet form, under multiple conditions, resulted in Nyquist plots indicating the material exhibited no detectable R CT (i.e., superconductivity). Correlation of the shift in the materials R CT with known structure/property changes for each sample with decreasing particle size allowed the development of a model explaining: (1) the significant increase in diamagnetic strength of the magnetically separated particles and (2) the mechanism controlling the material's R CT.

Study of soot microscopic characteristics in hydrogen/methane/ethylene co-flow diffusion flame

Hydrogen (H2) has been regarded as a highly competitive alternative fuel that does not produce CO2 and soot during combustion. However, the effect of hydrogen addition on soot formation and emission is questionable. The purpose of this paper is to study the influence of hydrogen/methane on the morphology of soot and the evolution of nanoparticle structure in laminar flame of ethylene. In this study, the soot morphology and nanostructure in H2/CH4/C2H4 laminar co-flow diffusion flames were investigated with thermophoretic sampling and high-resolution transmission electron microscopy (HRTEM). The results showed that the average primary particle diameters (Dp) of pure ethylene flame gradually decreased along the flame height direction, showing the competition between soot surface growth and soot oxidation. When the hydrogen is added into the fuel flow of ethylene, the Dp decrease at most sample points. Methane affects the inhibitory effect of hydrogen doping on soot, and with the increase of methane mixing ratio, the change trend of Dp of each hydrogen mixture with flame height is becoming more and more consistent. The nanostructure analysis showed that hydrogen doping made soot particles shorter, more tortuous and denser fringes. There is a synergistic effect to promote the growth of primary soot particles at low methane ratio, but it disappears after mixing 20 % hydrogen. The fringe length and tortuosity of soot particles gradually increase with the methane ratio.

Experimental study on soot formation and primary particle size in oxy-combustion ethylene diffusion flames under CO2 substitution for N2

This paper reports an experimental study on the effects of O2 concentration and CO2 concentration on soot volume fraction and primary particle size of flame centre in ethylene laminar co-diffusion flame. The incandescent light was induced by a two-color band method and laser-excited by wavelength 1064 nm. Previous studies have shown that the oxygen concentration affects the soot volume fraction in the flame. However, the effects of O2 concentration on the primary particle size under CO2 atmosphere are unclear and need to be further discussed. Seven flames were optically detected, in which the oxygen concentration of the accompanying gas varied from 21% to 50% by volume. One primary flame was burned in co-flowing ethylene/air. Six ethylene flames were burned in an oxygen-rich O2/N2 or O2/CO2 atmosphere with an oxygen mole fraction from 30% to 50%. The C2H4 flow rate remained constant in all operating conditions. The results show that the SVF observed by the LII method and spectroscopy in the oxygen-enriched flame are in good agreement. Furthermore, the soot's primary particle diameter measured by the time-resolved LII method is in good agreement with the transmission electron microscope image analysis.With the increase of oxygen concentration, the flame height becomes shorter, the luminosity becomes brighter, and the soot yield increases. Compared with an N2 atmosphere with the same oxygen concentration, the soot yield in a CO2 atmosphere was significantly inhibited. In all the flames studied, the SVF along the flame axis showed a similar distribution: it first increased to the maximum value and then decreased rapidly until the flame tip. The maximum SVF on the axis appears between 0.64 and 0.78 based on the normalized height of the visible flame. In all ethylene/(O2/N2) flames, the maximum primary particle diameter and average primary particle diameter increase with oxygen content. For ethylene/(O2/CO2) flame, the maximum diameter of primary particles decreases with the increased oxygen content. The uncertainty of primary diameter is mainly caused by the thermal adaptation coefficient, the lower LII signal of smaller particles and the uncertainty of local flame temperature.

Effects of ammonia on morphological characteristics and nanostructure of soot in the combustion of diesel surrogate fuels

The morphological characteristics and nanostructure of soot particles in pure n-heptane (C7H16) and n-heptane/ammonia co-flow diffusion flames were analyzed and compared using thermophoretic sampling and transmission electron microscopy (TEM) observation combining with quantitative image information extraction methods. The results showed that the overall formation and evolution of soot particles in NH3-doped n-heptane flames along the flame centerline were similar with that without NH3-doping. However, compared to n-heptane flame, the peak average diameter of primary soot particles and the peak gyration radius of soot aggregates in NH3-doped flames were reduced by about 45% and 37%, respectively, which indicated that the growth of both primary soot particles via surface reaction/condensation and soot aggregates via coagulation were significantly decreased. Meanwhile, the fractal dimension of soot aggregates was lower with NH3 addition as the structure of soot aggregates was looser and tended to be more chain-like. After NH3 doping, the peak average fringe length inside soot particles was decreased by 13%, and the inter-fringe spacing and tortuosity of soot were increased by 8% and 3%, respectively. This represented a more disordered microcrystal structure and lower degree of graphitization of soot particles, meaningfully indicating a higher oxidation reactivity.

Experimental effect of CuO2 nanoparticles into the RME and EGR rates on NOX and morphological characteristics of soot nanoparticles

In recent years, the adding nano additives to the fuel is paid much attention by decreasing the exhaust emissions and enhance combustion characteristics without any modifications in diesel engine. The effects of copper dioxide (CuO2) nanoparticles and exhaust gas recirculation (EGR) on combustion characteristics and morphological characteristics of soot nanoparticles in diesel engine fuelled with rapeseed methyl ester (RME) were investigated in this study. The good advantages of CuO2 nanoparticles such as good thermal properties, oxygen storage, and density thermophysical properties of viscosity are encourage to using as nano additives into the biodiesel. The results showed that the pressure inside cylinder and ROHR improved by 4% and 11%, respectively, from adding CuO2 nanoparticles into the RME in comparison neat RME. Furthermore, the BTE increased by 3.64%, 7.36%, 9.28% and 12.43% with adding CuO2 to the RME, while the BSFC decreased by 5.26%, 7.47%, 9.68% and 12.73% when adding nanoparticles to the RME under 25%, 50%, 75% and 100% of engine load, respectively, in comparison with diesel fuel. Adding CuO2 nanoparticles to the RME and 20% rate of EGR significantly decrease the NOX emissions by 29.64% when compared to the without nano additives. The number and concentration of soot nanoparticles were decreased with addition of CuO2 nanoparticles to the RME and they increased with presence EGR technology. It is indicated that the soot nanoparticles concentration decreased or was in par with neat RME when incorporation between EGR and nano additives. The morphological parameters such as number of soot primary particles (npo) exhibits significant reduction by 18%, meanwhile slightly increase in the average diameter of soot primary particles (dpo) by 7% with adding CuO2 to the RME for with and without EGR.

Simulating yield and morphology of carbonaceous nanoparticles during fuel pyrolysis in laminar flow reactors enabled by reactive inception and aromatic adsorption

Carbon black and soot are synthesized by gas-phase pyrolysis of hydrocarbons. Inception, surface growth, and coagulation control process yield and agglomerate morphology. Here, we present a sectional population balance model (SPBM) coupled with chemistry to simulate carbon black formation by ethylene pyrolysis in laminar flow reactors. The SPBM tracks agglomerate size distribution and morphology. New particles are formed by the dimerization of polycyclic aromatic hydrocarbons (PAHs) and grow with hydrogen abstraction acetylene addition as well as the addition of PAHs on their surface. Three different dimerization models for inception and PAH adsorption are compared: irreversible, reversible, and reactive. With irreversible PAH dimerization and surface growth, more than 90% of PAH mole fraction converts to particles even at low-temperatures (T<1200 K) causing an overestimation of the primary particle number density due to non-stop new particle formation. With reversible dimerization, the mass yield is underestimated by more than a factor of 3. With reversible dimerization and surface growth followed by a chemical bond formation step (chemical dimerization/reactive model), particles form and grow mostly at high temperatures (T>1200 K); the particle size distribution, as well as the average primary particle and mobility diameters are predicted within 30% of measurements. The reactive model enhances the agglomerate morphology prediction in the low-temperature regions of the reactor and appears to be more consistent with the latest understanding of inception and surface growth.

The influence of nitrogen and hydrogen addition/dilution on soot formation in coflow ethylene/air diffusion flames

Harmful emissions from combustion, such as soot, have severe adverse effects on the environment and human health. One way to mitigate these emissions and their dangerous influence is through fuel dilution. In the present study, the effects of adding different percentages of hydrogen and nitrogen to the fuel in a set of laminar coflow ethylene/air diffusion flames are investigated numerically by employing an in-house algorithm, the CoFlame code. The various influences of hydrogen, including dilution, density, transport, thermal, and chemical effects on soot formation and flame characteristics, are evaluated by introducing different fictitious species into the chemical mechanism. The numerical calculations of temperature, soot volume fraction, and average primary particle diameter of soot are in agreement with experimental measurements from the literature. Results show that blending hydrogen and nitrogen into the fuel decreases soot volume fraction and radiation. The hydrogen abstraction C2H2 addition (HACA) surface growth and polycyclic aromatic hydrocarbon (PAH) condensation rate reductions are responsible for the decrease in soot volume fraction. It is found that the soot formation/oxidation reaction rates are decreased under the dilution effect while increased under the transport and chemical effects. Among the various effects of hydrogen addition, the dilution effect has the most significant influence on soot formation/oxidation reaction rates. It is seen that the density and thermal effects have a negligible effect on soot volume fraction.

Surface growth, coagulation and oxidation of soot by a monodisperse population balance model

A monodisperse population balance model (MPBM) is developed here that capitalizes on the rapid attainment of the self-preserving size distribution and asymptotic fractal-like structure of agglomerates by coagulation to simulate their evolution with only three equations. Total agglomerate carbon molar, C, number (N) and area (A) concentrations are tracked. The model accounts for the polydispersity of agglomerates by enhancing their collision frequency by that of their self-preserving size distribution based on the radius of gyration in the free molecular regime. Scaling laws from detailed discrete element modeling (DEM) simulations are used to describe the fractal-like morphology of the agglomerates. The MPBM predicts the evolution of soot fv, N and average mobility and primary particle diameters during surface growth and agglomeration in laminar premixed ethylene flames as well as soot oxidation in a tube reactor within 30% of detailed DEM, sectional population balance simulations and measurements. Thus, when self-preserving size distribution and asymptotic structure of agglomerates are attained, this simple MPBM has unprecedented accuracy and can be readily interfaced with computational fluid dynamic (CFD) to model soot formation in combustion devices or process design and optimization for the synthesis of carbonaceous agglomerate nanoparticles.

The effect of low reactivity fuels on the dual fuel mode compression ignition engine with exergy and soot analyses

In this study, the effect of fuel injection timing of diesel on the dual fuelled compression ignition engine with gasoline, methanol and toluene has been investigated. Closed cycle combustion simulations have been conducted to complement the experiment results and for a better understanding of the in-cylinder dynamics. Second law of thermodynamics analysis has been done for the designing of energy recovery devices. Exhaust soot particles has been analysed by scanning electron microscopy to get soot particle structure. Distributions of soot particle number by size and particle mass by size have been investigated. Experiments have been conducted for respective premixed ratios of gasoline/methanol/toluene at different start of injection (SOI) timing of diesel. Outcomes revealed that the maximum gross indicated thermal efficiency (GITE) of 39% is obtained for gasoline/diesel mode. This mode shows 86% more oxides of nitrogen (NOx) in comparison with methanol/diesel mode at −25 crank angle degree (CAD) SOI case. About 54% more soot has been observed at −25 CAD SOI in toluene/diesel compared to that of gasoline/diesel mode. Maximum of 38.7% and minimum of 27.8% work exergies have been observed in gasoline/ and methanol/diesel modes respectively. Toluene/diesel mode shows the largest average primary particle diameter (Dp; 44 nm) among the dual fuel modes.

Determination of the volume fraction of soot accounting for its composition and morphology

The soot volume fraction, fv, is essential for combustion engineering, air quality and climate modeling. It is commonly obtained from mobility or optical data assuming soot spheres of constant composition that tend to overestimate fv by up to an order of magnitude. Here, a method is presented for estimation of the fv from soot mobility or optical diagnostics data accounting for the realistic soot morphology and composition. With mobility data, the fv is determined by a relation for soot morphology (fractal-like structure) and the average primary particle diameter from microscopy, gas adsorption or power laws. Such fv and the corresponding soot volume/mass size distributions are in excellent agreement with accurate but tedious soot mass-mobility measurements in premixed flames along various heights above the burner (HAB) as well as from the exhaust of diffusion flames and diesel engines. With light extinction data, the fv is obtained by explicitly accounting for soot composition (through its optical band gap and refractive index, RI) and the light absorption enhancement (due to multiple light scattering within soot agglomerates) in the absorption function, E(RI). So as nascent soot matures by surface growth and agglomeration, its optical band gap decreases while its mobility diameter, carbon to hydrogen (C/H) ratio and fv increase, increasing the soot E(RI) from 0.22 to 0.40, in excellent agreement with laser induced incandescence data from flat premixed ethylene flames. Using this variable E(RI), the soot fv from light extinction data in these flames is up to 50% lower than that using standard constant E(RI) for soot spheres.

Effect of operating conditions on the chemical composition, morphology, and nano-structure of particulate emissions in a light hydrocarbon premixed charge compression ignition (PCCI) engine

The aim of present work is to bridge the gap of knowledge concerning crystallite size, graphene layers curvature and inter-layer distance as nanostructure characteristics of soot primary particles, and also to comprehensively characterize the morphology of soot emission in a light hydrocarbon premixed charge compression ignition (PCCI) engine. In this study, the chemical composition, morphology and nano-structure of particulate emissions between conventional diesel and light hydrocarbon PCCI engine were performed with thermogravimetric analysis, gas chromatography mass spectrometry, and high-resolution transmission electron microscopy technology. The results show that the volatile matter content of light hydrocarbon is much higher than that of diesel, and thermogravimetry and differential thermogravimetry curves of light hydrocarbon shift to low temperature regions. The total organic components of particulate matter of light hydrocarbon PCCI engine are less, and the corresponding separation time is shorter. The structure of particles produced in light hydrocarbon PCCI engine is more open, and the size of aggregates is smaller. Fractal dimensions of 1.774 and 1.691 are obtained for soot particles in light hydrocarbon PCCI engine, compared to that of 1.81 and 1.785 in conventional diesel engine. Compared to conventional diesel engine, fringe separation distance and fringe tortuosity in light hydrocarbon PCCI engine are smaller while fringe length is larger. The primary particle nanostructures of light hydrocarbon PCCI engine incline to graphitize and change into the orderly structure. Compared with conventional diesel combustion, the average primary particle diameter of light hydrocarbon PCCI approximately reduces 2.0% at 75% load and 18.2% at 100% load, respectively.

A feasible and accurate method for calculating the radiative properties of soot particle ensembles in flames

The accurate calculation of the radiative properties of soot particle ensembles in flames needs to exactly reconstruct the geometric structures of all soot particles and accurately calculate the radiative properties of all soot particles based on their reconstructed geometric structures. However, the enormous number of soot particles in real ensembles makes it practically impossible to implement this task. To solve this problem, a feasible and accurate method is proposed for calculating their main radiative properties except scattering matrix and depolarization ratio. Experimental and numerical results show that soot particles with the same number of primary particles from the same sampling point can be considered as equivalent soot particles, which have almost the same volume, absorption cross-section, scattering cross-section and scattering asymmetry cross-section. Moreover, the average values of these quantities of equivalent soot particles approximately linearly increase with the number of primary particles. These findings can dramatically reduce the difficulty of reconstruction and calculation. The radiative properties of 37 different morphologies of soot particle ensembles in the visible and near-infrared regions (λ = 0.40–3.00 µm) are calculated using this method, and it is shown that the increasing of the average diameter of primary particles and the average number of primary particles per soot particle can enhance the absorption coefficient, scattering coefficient, asymmetry factor and single-scattering albedo of soot particle ensembles 0.1–900 times. In addition, these radiative properties are found to decrease by at least 70% with the increasing of λ from 0.40 µm to 3.00 µm.

The role of reactive PAH dimerization in reducing soot nucleation reversibility

Abstract Nucleation of incipient soot or carbon black nanoparticles has significant scientific and industrial importance because it influences the particle size distribution, morphology and composition, hence its health and environmental impact as well as functional properties. R eversible P olycyclic Aromatic Hydrocarbon (PAH) C lustering (RPC) with van der Waals forces (vdW) was proposed recently as opposed to I rreversible P AH C lustering (IPC) for soot nucleation (Eaves et al., Proc. Combust. Inst, 35 (2015) 1787) to relax the assumption of stable dimer formation with physical bonds at flame temperatures. Here, the necessity of considering chemical bond formation between PAHs in a dimer for reducing soot nucleation reversibility in ethylene coflow diffusion flames with a wide range of nitrogen dilution ratios is demonstrated. An RPC model with C hemical B ond F ormation (RPC CBF) is developed and its performance is compared to those of RPC and IPC models. Only the RPC CBF model with low reversibility for PAH addition on the surface of soot primary particles can predict soot volume fraction, average primary particle diameter, primary particle number density and the bimodal size distribution of soot agglomerates on the flame centerline within experimental uncertainty. While the IPC model overpredicts soot concentrations by a factor of five with increased dilution, the RPC model underpredicts it by more than two orders of magnitude for the flame with 68% nitrogen dilution. The RPC model fails to predict the observed bimodality of agglomerate particle size distribution in flames with low dilution because its predicted nucleation rate is much weaker compared to that of growth. Accounting for chemical bond formation for dimers is essential to form enough nuclei with increasing dilution and temperature. Also, low reversibility for PAH addition is required to predict the balance between nucleation and surface growth, hence the average size of soot primary particles.

Soot aggregate morphology in coflow laminar ethylene diffusion flames at elevated pressures

The effect of combustion pressure on soot aggregate morphology and on primary soot particle diameter was investigated by thermophoretic sampling in nitrogen-diluted ethylene flames. Soot aggregate samples were collected using a high-pressure thermophoretic sampling system installed inside the high-pressure combustion chamber. Collected samples were imaged by transmission electron microscopy followed by an automated image analysis process to yield aggregate morphology information. The experiments covered pressures from 3 to 6 bar, and samples were collected at heights of 2 and 5 mm above the burner exit in nitrogen-diluted ethylene (ethylene to nitrogen mole ratio 2:1) flames with nominal visible flame heights of about 20 mm. It was observed that average primary soot particle diameter increased with increasing pressure within the pressure range considered, at both measurement locations within the flame. Fractal parameters of the soot aggregates were inferred directly from the experimental data (as opposed to the usual practice of assuming a priori values for fractal dimension and pre-factor). Near to the soot nucleation and growth regions of the co-flow laminar diffusion flames, at 2 mm above the burner exit, the fractal dimension of the aggregates was not as high as the accepted universal value of about 1.9, in spite of the fact that number of primary particles per aggregate is quite high and pressure is well above atmospheric. At 5 mm above the burner exit, however, the fractal dimension of the soot aggregates approached the accepted universal value of 1.9, at high pressures; at relatively lower pressures, the fractal dimension was about 1.6 at the same location within the flame. In view of the inferred fractal results, caution should be exercised when applying fractal analysis to low heights in flames at lower pressures where soot inception and growth are relatively dominant.

Morphological analysis of soot agglomerates from biodiesel surrogates in a coflow burner

The effects of unsaturation (including the C–C double bond's position in the alkyl chain) and the ester moiety in the fuel molecule on the morphology of soot particles in a laminar coflow diffusion flame are studied. The effects of the ester moiety are evaluated by comparing an n-decane flame with a biodiesel surrogate flame (composed of 50%/50% molar blend of n-decane and methyl octanoate). The effects of the unsaturation and the position of C–C double bond in the alkyl chain are analysed by comparing 1-decene, 5-decene and n-decane flames. Particles were collected thermophoretically on Transmission Electron Microscopy (TEM) carbon coated copper grids. TEM images are analysed to obtain parameters related to the size of the agglomerates such as radius of gyration, and morphological parameters such as fractal dimension and prefactor of the power-law relationship. The results show that the average primary particle diameter, the size of the agglomerates and the number of primary particles composing the agglomerates increase along the flame length to around two thirds of the flame length and then decrease as a consequence of oxidation becoming dominant over soot nucleation and growth. The fractal dimension of the agglomerates does not change significantly along the different pathlines of the flames. However, effects of the fuel chemical structure are clear. The lowest fractal dimensions are observed for the oxygenated fuel and the highest ones for the unsaturated fuels, with higher fractal dimension when the double bond is located at the edge of the molecule. The same trends are observed for agglomerate sizes: smallest agglomerates are observed for the oxygenated fuel and largest ones for the unsaturated fuels. This suggests that low soot-emitting fuels reduce their size as a consequence of oxidation while keeping their agglomeration skeletal structure.

Development of a method to characterize chain-like aggregates in diffusion flames using dynamic light scattering.

A new method is presented that can yield particle-size distribution parameters and aspect ratios for chain-like aggregates in a diffusion flame using dynamic light scattering (DLS). Measurements of polarized and depolarized correlation functions are carried out in a Fe(CO)5-seeded CO-O diffusion flame as function of position above the burner surface. The measurements are combined with the method of cumulants to yield, for the first time to our knowledge, both the translational and rotational diffusion coefficients of chain-like aggregates along the axis of symmetry of the flame in the temperature range 863-1087 K. The average primary particle diameters inferred from DLS are compared with the results of transmission electron microscopy analysis and the differences are less than 12%. Furthermore, the aspect ratios of the chain-like aggregates are combined with their residence time in the flame to yield aspect ratio growth rates of (5.33±0.30)/s. It is demonstrated that the laser beam Gaussian factor needs to be considered in the data analysis in order to obtain physically meaningful results. In addition, the limitations of the approach are discussed.

Investigation of the High-Rate Recharging Mechanism in LiMn2O4 By Primary Particle Analysis

IntroductionThere were two types of lithium manganese oxide (LiMn2O4) supplied by different supplier. They showed similar crystal structure according to the XRD analysis, but the Li+ charging/discharging rate was quite different. To elucidate the working mechanism of this performance difference, we applied the SEM, AC impedance, and ESR measurement on LiMn2O4particles. Results and discussion of the experimentalTwo kinds of the lithium manganese oxides were used as the active material. The active material as the electrode, was implanted in the gold wire without any binder and conductive additive (99.99%). 1M LiPF6 / EC + DEC (1: 1 volume ratio) was used as the electrolyte, silver is used as a quasi-reference electrode, it was used platinum as a counter electrode. In this experiment was measured the Cyclic voltammogram of the high-rate lithium manganese oxide (HR-LMO) and non-high-rate lithium manganese oxide NHR-LMO at the potential sweep rate v of 200 mV/s. The HR-LMO was continuously observed the two peaks. However, the NHR-LMO was not observed.The SEM samples of the cross-section of the active material was prepared using an FIB system. The cross-sectional SEM photograph, was performed at an accelerating voltage of 5 kV using the LV-SEM.In this experiment the average particle diameter of primary particles is 30 nm in the HR-LMO, NHR-LMO were hundreds of nanometers at 10 times or more. This finding indicated that the rate performance of the active material was affected by the primary particles size.The active material was placed into the impedance measurement jig (S = 1260 mm2, d = 0.9 ± 0.3 mm). The impedance |Z| and phase angle θwere measured by using the LCR meter (NF Corp., ZM-2355).The impedance |Z| of the HR-LMO and the NHR-LMO were 5 kΩ and 200 kΩ, respectively. The phase angle θwere -30 ° and -65 °, respectively. This finding indicated that the active material of the high rate performance was low impedance.5 mg of active material were placed into the cylindrical glass sample tube (inner diameter of 1 mm) as the ESR measurement tube, and the mass of the active material was measured. The ESR measurement tube was placed at the center in the ESR resonator. The ESR spectrum was observed by using the ESR spectrometer (JEOL, JES-RE3X).The ESR signal of g=2.0 and ΔH=22.2 mT were observed in the HR-LMO. However, the ESR signal was not observed in the NHR-LMO. The ESR signal of g=2.0 may be due to electrons in conduction band, because this value is approximated to g=2.0023 of free electrons.