Fringe Separation Research Articles

Comparative nanostructure analysis of gasoline turbocharged direct injection and diesel soot-in-oil with carbon black

Two gasoline turbocharged direct injection (GTDI) and two diesel soot-in-oil samples were compared with one flame-generated soot sample. High resolution transmission electron microscopy imaging was employed for the initial qualitative assessment of the soot morphology. Carbon black and diesel soot both exhibit core-shell structures, comprising an amorphous core surrounded by graphene layers; only diesel soot has particles with multiple cores. In addition to such particles, GTDI soot also exhibits entirely amorphous structures, of which some contain crystalline particles only a few nanometers in diameter. Subsequent quantification of the nanostructure by fringe analysis indicates differences between the samples in terms of length, tortuosity, and separation of the graphitic fringes. The shortest fringes are exhibited by the GTDI samples, whilst the diesel soot and carbon black fringes are 9.7% and 15.1% longer, respectively. Fringe tortuosity is similar across the internal combustion engine samples, but lower for the carbon black sample. In contrast, fringe separation varies continuously among the samples. Raman spectroscopy further confirms the observed differences. The GTDI soot samples contain the highest fraction of amorphous carbon and defective graphitic structures, followed by diesel soot and carbon black respectively. The AD1:AG ratios correlate linearly with both the fringe length and fringe separation.

Soot reduction by addition of dimethyl carbonate in normal and inverse ethylene diffusion flames: Nanostructural evidence

Oxygenated fuel represents an attractive alternative as an additive for reducing soot emissions. Dimethyl carbonate (DMC) is an oxygenated compound which is a good option to reduce soot, but the detailed characteristics of soot produced from combustion of hydrocarbon fuels blended with DMC are still lacking. The present research studied the nanostructure and reactivity of soot particles in ethylene/DMC normal and inverse diffusion flames. High resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were used to analyze the nanostructure and reactivity of soot. It was found that DMC addition was effective in decreasing the average weights of soot formed in flames. The results of HRTEM images showed that soot particles obtained with DMC addition showed liquid-like material and tight bonding, and exhibited more highly disorganized layers, which give it higher reactivity than soot obtained without DMC addition. Furthermore, HRTEM was used to analyze soot fringe characteristics consisting of fringe tortuosity, fringe length, and fringe separation. XRD was used to crosscheck the results for fringe separation, and was consistent with HRTEM results. In addition, the mass loss curve of TGA experiments showed that DMC addition could enhance the reactivity of soot particles.

The influence of a large methyl ester on in-flame soot particle structures in a small-bore diesel engine

Oxygenated biodiesel presents lower sooting propensity than conventional diesel, providing a good opportunity to resolve the high particulate emissions issue. This study reports soot morphology details of methyl decanoate, a selected surrogate fuel for the larger fatty acid methyl esters in biodiesel. The size distribution of soot primary particles and aggregates as well as the fractal dimension of the aggregates are discussed in comparison to those of a conventional diesel fuel. In addition, nanoscale soot parameters such as carbon fringe length, tortuosity, and fringe-to-fringe separation distance are analysed to clarify the internal structure variations depending on the fuel type. Of particular interest are the structures of soot particles within the flame in a running diesel engine. Compared with numerous previous studies reporting exhaust soot particle structures of biodiesel, the present study provides additional and complementary information about soot particles under high formation and oxidation processes during the main combustion event. Thermophoresis-based soot particles collection was conducted in a small-bore optical diesel engine using a sampling probe placed within the combustion chamber for the direct exposure of a transmission electron microscope (TEM) grid to sooting flames. The TEM images were post-processed for statistical analysis of the aforementioned morphology and nanostructure parameters. The results show that methyl decanoate generates smaller soot primary particles and aggregates with lower fractal dimension, which could be explained either by the earlier stage of soot formation or more oxidised soot status. From the fringe separation results showing a smaller gap for methyl decanoate, it is concluded that the sampled in-flame soot particles were more oxidised likely due to the presence of oxidisers in fuel.

Nanostructure analysis of particulate matter emitted from a diesel engine equipped with a NTP reactor

An investigation of the nanostructures of particulate matter (PM) emitted from a diesel engine equipped with a non-thermal plasma (NTP) after-treatment device was conducted. Raw PM, PM escaping from the NTP reactor (PM-NTP), and PM collected on the collection plate (PM aggregation) were sampled at different engine loads. High-resolution transmission electron microscopy (HRTEM) images were used to analyse the nanostructures. Raw PM showed onion like structures with short lattice fringes, however, core-shell like structures were observed for PM sampled at 60% engine load after exhaust flowed through the NTP reactor. The diameter decreased for PM-NTP and PM aggregation compared with raw PM, regardless of the engine loads. The core-shell like structures were evident after PM was partially oxidized. The average fringe separation distance, length, and tortuosity were 0.95–1.26nm, 2.90–3.70nm, and 1.45–1.97 respectively. The fringe separation distance increased with increasing engine load for the same kind of PM. The influence of plasma on the changes of nanostructure parameters was greatly dependent on the engine loads. The fringe length dominated the changes of the instantaneous activation energy during the oxidation process, while it was less important for apparent rate constant.

Morphology, fractal dimension, size and nanostructure of exhaust particles from a spark-ignition direct-injection engine operating at different air–fuel ratios

This work studied the physicochemical characteristics of exhaust particles from a 1.48LSIDI engine operating at different air–fuel ratios (AFRs). The morphology, fractal dimension, size and nanostructure were characterized using high-resolution transmission electron microscopy (HRTEM) in conjunction with electron energy-loss spectroscopy. The results indicate that SIDI aggregate particles produced at varying AFRs exhibit different morphologies. TEM images show that the aggregates obtained at an AFR of 14.7 are more compactly clustered than those generated under fuel-rich and fuel-lean conditions. The fractal dimension of SIDI aggregates at an AFR of 14.7 is found to be 2.21, a value that is larger than those from other AFRs. The primary particle sizes are distributed over a wide range of 5–55nmat all AFRs, although the largest average primary particle diameter is found at an AFR of 14.7. Similar to diesel soot particles, SIDI soot particles also show characteristic shell-core and turbostratic structures at the nanoscale level. At an AFR of 14.7, the soot particles have a relatively short fringe length, a small fringe separation distance and high fringe tortuosity. As the AFR is increased, the sp2/sp3 hybridization ratios first gradually decrease and then increase, with a minimum value of 0.156 at AFR=14.7. SIDI soot particles are likely more reactive than diesel soot particles because they possess the relatively short fringe length, large separation distance and high tortuosity.

Quantitative study of the macromolecular structures of tectonically deformed coal using high-resolution transmission electron microscopy

Tectonic deformations damage the macrostructure and impact the macromolecular structures of coal. In this study, high-resolution transmission electron microscopy (HRTEM) was applied to observe the macromolecular structures of six different types of tectonically deformed coal, and quantitative analyses were conducted by using image analysis algorithms to extract the images of lattice fringes to obtain the following three structural parameters: fringe length, fringe tortuosity and fringe separation. The results show that coal rank has an important influence on the macromolecular structures of coal, and this effect varies with different stages of metamorphism. For weak tectonically deformed coal, increases in coal rank indicate an increase in fringe length and decrease in fringe separation and fringe tortuosity. The increments in the fringe separation and fringe length first increase and then decrease, and the maximum values occur during the evolution from mid metamorphic stage to high metamorphic stage. Fringe tortuosity shows a gradually decreasing trend. Tectonic deformation also has an important influence on the macromolecular structure of coal, and this effect varies with different stages of coal rank. With decreases of tectonic deformation, fringe length is increased and fringe separation and tortuosity are decreased; however, the impact of tectonic deformation on the macromolecular parameters of low-rank coal is stronger than that of the mid-rank coal. The impacts of tectonic deformation on the nanoscale pores, coal methane adsorption capacity and coalbed methane contents of low-rank coal are higher than those of the mid-rank coal.

Atom force microscopy analysis of the morphology, attractive force, adhesive force and Young's modulus of diesel in-cylinder soot particles

In this paper, the morphology, attractive force (Fat), adhesive force (Fad) and Young's modulus (EY) of diesel in-cylinder soot particles sampled by a total cylinder sampling system were studied using atom force microscopy. In each combustion phase, the equivalent diameter (ED), Fat, Fad, adhesion energy and EY present broad distributions. The pattern of ED distribution in the late combustion phase is similar to that in the late diffusion combustion phase, especially in the range of ED < 10 nm, suggesting that the particle size distribution changes little after the late diffusion combustion phase. Most isolated soot particles in each combustion phase possess a very low sphericity ratio. Three types of force curves are discovered for in-cylinder particles, and are introduced to identify the particle types. For the test carbonized soot particles, the SR appears to increase with an increase in ED in each combustion phase, and the AED shows a similar trend to that for all test particles during the combustion process. Due to the presence of plastic deformation for the nascent soot particles and the penetration for the liquid materials during the force measurement, the carbonized primary soot particles are employed for force analysis. As the combustion proceeds, the population-averaged values of Fat and Fad show opposite trends; the attractive force, which is mainly driven by the Van der Waals force, gradually decreases. During the combustion process, the population-averaged adhesion energy decreases to a minimum in the late premixed combustion phase after which it then increases. The initial increase in the population-averaged Young's modulus (AEY) is followed by a decrease before gradually increasing again from the early diffusion combustion phase. The AEY shows a negative correlation with the fringe separation distance in the soot structure.

Impact of intake hydrogen enrichment on morphology, structure and oxidation reactivity of diesel particulate

Experimental investigations were conducted on a 4-cylinder natural-aspirated direct-injection diesel engine with naturally aspirated hydrogen, focusing on the effects of hydrogen addition on the physico-chemical properties of the diesel particulate. Diesel particulates were sampled for off-line analysis, with the aid of TEM and TGA facilities. Hydrogen addition promotes particle oxidation at low engine load and speed due to the increase of exhaust temperature, resulting in smaller particles, but it inhibits particle oxidation at high engine load due to the competition of oxygen between hydrogen and diesel fuel which results in larger primary particles. The replacement of injected diesel fuel by hydrogen inhibits the formation of soot nuclei and decreases its volume density, hence reduces the size of aggregate particles which are more spherical as indicated by an increase of fractal dimension and a decrease of radius of gyration. With increase of engine load, primary particles exhibit more graphitic structure, changing from “onion like” to “shell–core” structure. Hydrogen addition promotes and inhibits primary particle oxidation at low and high engine loads, respectively, and the corresponding primary particles are “turbostratic interlayer” and “shell-amorphous” in structure, respectively. The results of recognized fringe length, tortuosity and fringe separation distance are consistent with the observed morphology. The oxidation reactivity is related to equivalence ratio, being higher at low engine load and speed, which is indicated by the variation of activation energy and ignition temperature. The oxidation reactivity is validated to be related to the nanostructure of primary particles.

Spectral fringes in non-phase-matched SHG and refinement of dispersion relations in the VUV.

We consider second harmonic generation (SHG) of ultrashort pulses in the case of strong phase- and group-velocity mismatch. Spectral fringes appear in the second harmonic related to two delayed replicas of the fundamental pulse in the time domain. The fringe separation can be used to evaluate the group-velocity and refractive index of nonlinear crystals at extreme wavelengths. Experimental results with femtosecond pulses in SrB(4)O(7) (SBO) are used to refine the Sellmeier equation describing the n(c) refractive index down to 160 nm, essential for the use of this unique nonlinear crystal for random quasi-phase-matching in the VUV.

A comparative study of the physical properties of in-cylinder soot generated from the combustion of n-heptane and toluene/n-heptane in a diesel engine

This study examines the similarities and dissimilarities in the physical properties of in-cylinder soot obtained during combustion of n-heptane and a toluene/n-heptane mixture (TRF20, 20% toluene by volume) in a heavy-duty diesel engine. A total cylinder sampling system was used to sample the in-cylinder soot during different combustion phases. For each sample, the morphology, size, fractal dimension and nanostructure of the soot particles were analyzed using high-resolution transmission electron microscopy and Raman scattering spectrometry. The oxidation reactivity of soot particles was also evaluated in terms of apparent activation energy using thermogravimetric analysis. Throughout the combustion process, soot aggregates from the combustion of TRF20 generally exhibited more primary particles and larger-sized clusters than the n-heptane soot aggregates. Despite the different fuel formulations, both n-heptane and TRF20 showed similar trends during the combustion process in terms of changes in fractal dimension of soot aggregates, mean primary particle size and nanostructure (as characterized by fringe length, separation distance and tortuosity). The presence of toluene, however, led to a decrease in the fractal dimensions of the aggregates and a concurrent increase in the mean size of primary particles. Moreover, in the same combustion stages, the mean fringe length for the TRF20 soot was smaller than that for the n-heptane soot, while the mean separation distance and tortuosity for the TRF20 soot were both larger than those for the n-heptane soot. Relative to the n-heptane soot, the TRF20 soot had less graphitic organization and lower resistance to oxidation.

Time-resolved light scattering studies of Spin-coated titanium dioxide

Spin coating of titanium alkoxides is a fast and straightforward method of forming compact and durable titanium dioxide thin films. In this report, an optical interference technique is used to understand the dynamics of titanium dioxide thin film formation during the spin coating process of titanium (IV) ethoxide sols, and a 4-stage thinning model is proposed. Optical monitoring of interference fringes as a function of time enables determination of the time-dependent film thickness through measurement of the interference fringe separation while the sol to gel transition can be monitored by analyzing the fringe visibility. For films that are spun at 2,000 rpm or faster, a spin duration of 5 s is sufficient for the film to reach its final thickness. At a given spin speed, spin times longer than 5 s do not affect the final film thickness. However, thinner final film thicknesses can be achieved by increasing the spin speed. All films were found to densify on annealing with an annealed thickness approximately 0.4 times that of the pre-anneal thickness regardless of spin speed. Spin-coated titanium dioxide films are expected to play an important role in low-cost and scalable next generation solar cells employing dyes and quantum dots as the light harvesting agents.

Interferometry Analysis of Cellophane Birefringence

This paper reports on a simple approach of determining the ability of a transparent material, such as cellophane to rotate the direction of polarization of a light beam. In order to determine the birefringence of such a material, a Mach-Zehnder interferometer is used to generate interference patterns when the cellophane sheet is mounted on one arm such as to intercept a portion of the laser beam. The recorded interferograms show a phase shift which is calculated to be 0.98π radians. By rotating the cellophane sheet on the object beam, the fringe separation is measured for different angles and the values used to calculate the ordinary and extraordinary refractive indices as 1.4721 ± 0.0002 and 1.4680 ± 0.0002 respectively at 632.8 nm wavelength. A surface error of approximately λ/16 (peak to valley) is measured from the recorded interferograms. Because of its sufficient birefringence and small thickness of 24 μm, cellophane can be used to fabricate special polarization pupil masks by cutting and aligning different cellophane structures appropriately.

Two-dimensional performance of uniform irradiation with the use of a concentricity deviation lens array and partially coherent light

A method of employing a lens array (LA) and partially coherent light (PCL) is presented for uniform irradiation on targets in inertial confinement fusion. Quasi-near field spots with a profile of sharp edge and flat top can be obtained with an LA, while the spatial coherence of the incidence beam is reduced by PCL. An appropriate concentricity deviation (CD) of LA results in the superposition of beamlets at the focus dislocated by a small amount each other and the CD and PCL reduce the fringe separations, thus the interference fringes become denser and the small-scale intensity non-uniformity of intensity distribution is suppressed. Based on the generalized diffraction integral theory, the intensity distribution of a Gaussian Schell Beam (GSB), point focused by an LA and a spherical lens is investigated in detail by two-dimensional simulation. And irradiation uniformity effects are compared with coherent light and partially coherent light after the LA. Numerical results indicate that using an appropriate CD and moving the target slightly from the exact focal plane of the principal focusing, a well-irradiated laser spot and great energy efficiency can be obtained.

A comparison of soot nanostructure obtained using two high resolution transmission electron microscopy image analysis algorithms

The present work addresses the validation process of an in-house developed image analysis tool to extract fringe length, tortuosity, and separation from high resolution transmission electron microscopy images of carbonaceous materials. In order to validate the algorithm, we compare fringe properties that are extracted from high resolution transmission electron microscopy (HRTEM) images through (1) the in-house developed tool (new algorithm) and (2) a tool that has been validated and published (previous algorithm). X-ray diffraction and Raman spectroscopy are used to crosscheck the results for fringe length and fringe separation extracted from the HRTEM images. The algorithm of extracting fringe tortuosity is validated by the images of two disordered soot samples, and a heat-pretreated, highly-ordered sample. Tortuosity results are compared with the results of fringe separation. These comparisons validate the algorithm for extracting fringe tortuosity and confirm that tortuosity is an indicator of the degree of disorder within the carbon framework. Statistical results for each property extracted from the HRTEM images by the newly developed image analysis tool are presented in the form of a histogram and characteristic values (mean and median). The characteristic values quantitatively distinguish between the different carbon nanostructures of various soot samples.

Development of an HRTEM image analysis method to quantify carbon nanostructure

An analytical method for analyzing high-resolution transmission electron microscopy (HRTEM) images is presented. The method is composed of two major parts: digital image processing and lattice fringe characterization. The digital image processing is composed of the following operations: negative transformation, region of interest (ROI) selection, contrast enhancement, Gaussian lowpass filter, top-hat transformation (used to correct uneven illumination across an image), thresholding to obtain a binary image, morphological modification, clearing fringes on the ROI border, skeletonization, and removing short fringes that lack physical meaning. These operations are defined by equations with effects illustrated by images. The lattice fringe characterization generates statistics on fringe length, tortuosity, and separation based on the skeletons of the graphene layers. Fringe length and tortuosity are obtained automatically from the features of the skeletons, while fringe separation is obtained by analyzing manually selected fringe pairs. The algorithms are implemented within MATLAB, and demonstrated upon an exemplary HRTEM image of carbonaceous material. The image analysis algorithm permits quantitative HRTEM, here specifically addressing nanostructure of carbonaceous materials.

Evolution of the nanostructure, fractal dimension and size of in-cylinder soot during diesel combustion process

The nanostructure, fractal dimension and size of in-cylinder soot during diesel combustion process have been investigated for a heavy-duty direct injection diesel engine, using a total cylinder sampling system followed by high-resolution transmission electron microscopy and Raman scattering spectrometry. Different structural organizations of in-cylinder soot are found depending upon the combustion phase. It is revealed that both the fringe tortuosity and separation distance decrease as combustion proceeds, while the mean fringe length increases distinctly from 1.00 to 2.13 nm, indicating the soot evolution toward a more graphitic structure during the combustion process. The fractal dimensions of aggregates are in a range of 1.20–1.74 at various crank angles under the applied engine operating conditions. As temperature and pressure increase, the fractal dimension decreases significantly to a minimum at the early diffusion combustion stage. The soot particles become more compact again as the fractal dimension increases during the subsequent combustion period. Primary particle sizes start small, go through a maximum in the early diffusion combustion phase and decline again as combustion proceeds.

Spatial interference from well-separated split condensates

We use magnetic levitation and a variable-separation dual optical plug to obtain clear spatial interference between two condensates axially separated by up to $0.25$ mm---the largest separation observed with this kind of interferometer. Clear planar fringes are observed using standard (i.e., nontomographic) resonant absorption imaging. The effect of a weak inverted parabola potential on fringe separation is observed and agrees well with theory.

Polarimetric stellar interferometry by use of birefringent retarders

We propose a polarimetric technique for a stellar interferometer that uses two birefringent retarders inserted into each arm of the interferometer. The retarders shift the interference fringes of the two orthogonal polarizations to opposite directions along an optical path difference (OPD), which enables us to measure the polarized fringe visibilities separately. Laboratory demonstrations were carried out using quartz retarders with a thickness of 1.124 mm, and the separation of the interferometric fringes of +/-10 microm along the OPD was observed. We discuss a calibration method for the acquired fringes to obtain reliable estimations of polarized fringe visibilities. We also discuss feasibility of the proposed technique for the Mitaka optical InfraRed Array (MIRA-I.2).

Deformation and Rigid-body-motion Measurement by Multiple Interferometric Strain/Slope Rosettes

In Part I, the Multi-ISSR measurement theory was given and validated for a three-indentation ISSR. Part II shows how fringe analysis is carried out by applying the theory to real measurement problems. Two-dimensional image processing techniques are applied to both the ISSR and the Multi-ISSR. The procedures are demonstrated through a bending experiment where a four-indentation Multi-ISSR is used. A practical example is given to demonstrate the numerical procedure involved in extracting the diffraction pattern, and calculating the shift of the zero- order diffraction peak to measure rigid-body-motion. Fringe pattern analysis includes numerical fringe separation and phase shift determination. Three practical approaches of obtaining strains by solving the governing equations relating phase shifts with strains and rigid-body-motion are discussed.

Multi-walled boron nitride nanotubes composed of diverse cross-section and helix type shells

High-resolution transmission electron microscopy (HRTEM) and electron diffraction analysis were performed on pure multi-walled novel type boron nitride nanotubes (BNNTs) by using a field-emission high-resolution 300 kV transmission electron microscope JEM-3100FEF (Omega filter). In contrast to commonly observed monochiral multi-walled BNNTs, the present tubular shells within every individual BNNT (up to ∼50 shells) revealed the whole range of helixes, i.e., from zig-zag to arm-chair. This being paired with the wide variations in cross-sectional tubular shapes, i.e., from a faceted polygon to a cylinder, results in complex overall tubular structures. The BN atomic lattice fringe separations, down to 1.25 A, on most symmetrical arm-chair (d10-10=1.25 A) and zig-zag (d11-20=2.15 A) tubular wall fragments within the same multi-walled BN nanotubes were ultimately achieved during HRTEM.