Search

The relationship between soot surface growth, soot nanostructure and reactant temperature (Tr) in a coflow diffusion ethylene flame was investigated with multiple experimental techniques. The Tr was raised by heating the coflow air. Three cases, with 300K, 473K, and 673K Tr, respectively, were studied. Laser-induced Incandescence revealed that increasing Tr promotes soot formation. Although soot primary particle diameter (dp) also increases with Tr, the increase in dp slows down after 473K Tr, suggesting that there is a deceleration in soot surface growth. Transmission Electron Microscopy (TEM) imaging showed that increased Tr promotes soot aggregation and yields larger and more mature primary particles. The assessment of the Selected Area Electron Diffraction (SAED) patterns indicated that, at 673K Tr, there is a growth of lattice planes. Raman spectroscopy revealed further structural details. By assessing the band intensity ratios, soot for the Tr of 673K has more curved nanostructures. The deceleration of soot surface growth may be explained by surface aging, which is characterized by an increase in curved nanostructures.

Understanding carbon black's oxidation behavior and resistance is crucial to its effective manufacturing, aftertreatment, and applications. This study combines well established bulk oxidation techniques, with novel in situ electron microscopy to visualize and establish oxidation pathways dependent on nanostructure and oxidation species. Three sample batches of carbon black were prepared; untreated, heat treated at 1400∘C, and 1600∘C. Heat treatment of the samples generated a graphitic shell highly resistant to oxidation by molecular oxygen. The sample oxidation pathways were then fully characterized using thermogravimetric analysis (TGA) and environmental transmission electron microscopy (ETEM). The TGA allowed for ex situ reactivity studies with molecular oxygen. The ETEM provided a real-time topographical and cross-sectional view of the particles as they oxidized under ionized O radicals and O2. Oxidation for all samples followed a three-step pathway: surface oxidation, nanotunnel formation through the surface, and bulk, diffusive carbon oxidation by O2. Amorphous samples oxidized rapidly with molecular O2. However, when O radicals were present, the amorphous sample reacted with O radicals to form a resilient carbon oxide, slowing oxidation. The heat-treated samples followed opposite trends; they resisted oxidation with O2 and reacted quickly with O radicals, as the radicals stripped away the graphitic shell.

The mechanistic pathways of PAH formation and growth remain uncertain. In addition, our current understanding of the transformation of PAHs into young soot is limited. The PAHs participating in this transformation remain ambiguous. Simultaneous measurements of PAHs and particles are necessary to better understand how particulates are formed in flames. A comprehensive analysis has been performed on a n-dodecane doped methane coflow diffusion flame. PAHs have been analyzed with GC/MS while the particulates have been collected from the flame centreline for studying under a Transmission Electron Microscope (TEM). The soot measurements from a previous study have been used to complete the comprehensive analysis. The novelty of the current study lies in the fact that it provides quantitative information on the growth of PAHs ranging from naphthalene (A2) to pyrene and fluoranthene (together they are referred to as A4 in this study) and how these species participate in the formation, growth and aging of the young soot. The experimental results show that before the commencement of the young soot, the gaseous phase is dominated by species equal to and smaller than A4. PAHs larger than A4 were not detected. With the growth of the young soot, the mole fraction of A4 decreases. The results suggest that small and medium-sized PAHs (A4 and smaller) are responsible for the formation and growth of the young soot. As the young soot transform into mature solid soot, A4 increases abruptly. The study shows that PAH growth and soot maturity are not mutually exclusive. The target flame has also been simulated numerically to identify the problems associated with the state-of-the-art model. The numerical model with irreversible nucleation can not capture the formation of young soot even though it considers nucleation from A4. A comprehensive database of PAHs and soot has been created for future numerical model validations.

Airborne soot is a product of incomplete combustion from engines and industrial processes. Unburnt soot is carcinogenic, a major contributor to climate change, and detrimental to combustor lifespan and efficiency. An understanding of how high-pressure combustion affects the oxidation properties of soot is crucial for the design of clean-burning, high-pressure engines and downstream soot filtration technologies. This paper presents the first real-time look at the oxidation of soot particles formed at high pressure and demonstrates that the oxidation pathway changes as combustor pressures increase. Soot particles were formed in an ethylene-fueled diffusion flame, with pressures ranging from 1 to 25 bar, and were subsequently sampled and oxidized inside an ETEM allowing for the nanoscale, real-time observation of oxidation pathways. The high-pressure generated soot grew larger in diameter, formed larger aggregates, and developed graphitic outer shells, protecting the reactive amorphous carbon core. The graph...

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.

Different non-intrusive optical and intrusive non optical diagnostic methods are used to measure flame and soot properties in a laminar coflow diffusion flame in order to compare and analyze the sensitivity of each technique to soot particles with different age and morphology. Flame temperature is measured using rapid thermocouple insertion (RTI) method and also by measuring soot spectral emissions (SSE). Soot volume fraction ( f v ) is measured quantitatively with laser extinction (LE), time resolved laser induced incandescent (TiRe-LII) and SSE methods and qualitatively from the transmission electron microscope (TEM) images of the thermophoretically sampled soot particles. Particle internal/aggregate nanostructure, and primary particle diameter are also analyzed based on TEM images from the sampled particles and TiRe-LII. It is shown that the optical methods are only sensitive to mature soot particles with solid appearance and cannot detect either temperature or f v in regions where liquid like nascent soot particles are dominant. f v measured by LE and TiRe-LII agree well while the values measured by SSE are lower. This discrepancy is attributed to the high sensitivity of f v measured by SSE to the measured temperature values. Temperature profiles measured by SSE are considerably higher than the values measured by RTI. It is shown that not considering the change of the surface emissivity of the thermocouple junction due to particle deposition for estimating radiation loss in regions where nascent or mature soot particles are dominant contributes to this discrepancy. Primary particle sizes measured based on TEM images and TiRe-LII agree reasonably well. Soot aggregate fractal dimension is shown to decrease as the soot particles age and become more mature.

The oxidation of soot, obtained from 1-decene and ethylene flames, in a mixture of ionized and molecular O 2 , was observed in real time by environmental transmission electron microscopy for the first time. The oxidation mode (surface vs. internal), and rate, was measured for individual primary particles, demonstrating that mature primary particles primarily oxidize through surface reactions. Further experiments with less mature soot particles showed oxygen permeation into the core of the primary particles, causing internal oxidation, as well as surface reactions, demonstrating a link between soot ageing and the oxidation mode. Aggregate structural changes and fragmentation throughout oxidation were also characterized; with surface reactions weakening the bridges between primary particles until the aggregate breaks up. In the last stages of aggregate oxidation, the primary particles were seen to lose their graphitic shell and spherical nature, with the remaining disordered carbon reforming into large amorphous masses before burning away. The role of ionized oxygen species on oxidation rates is also discussed, and showed a strong dependence on electron beam voltage.

Structural effects of biodiesel in terms of unsaturation, i.e. C=C double bonds, its position and the presence of the ester moiety on soot formation are studied in this paper. Laminar coflow diffusion flames of 5-decene, 1-decene, n-decane, and a biodiesel surrogate consisting of a 50%/50% molar blend of n-decane and methyl-octanoate are selected for the investigation. It is observed that the presence of unsaturation promotes soot formation in the flames by increasing soot chemical surface growth species and soot inception species (aromatics) as it is evident from the larger primary particle size and number density of soot particles in the 1-decene, and 5-decene flames compared to the n-decane flame, respectively. More centrally located C=C double bond further speeds up soot inception as it promotes the formation of aromatic species. This is also evident from earlier detection of soot on the centerline and higher soot primary particle number density of the 5-decene flame compared to 1-decene and n-decane flames measured by the laser extinction and thermophoretic sampling methods, respectively. Effects of the ester moiety on soot formation are more on the concentrations of soot chemical surface growth species because the biodiesel surrogate flame has similar number density of primary particles compared to the n-decane flame but soot primary particles have smaller diameters.

Through billions of years of evolution, microorganisms mastered unique swimming behaviors to thrive in complex fluid environments. Limitations in nanofabrication have thus far hindered the ability to design and program synthetic swimmers with the same abilities. Here we encode multi-behavioral responses in microscopic self-propelled tori using nanoscale 3D printing. We show experimentally and theoretically that the tori continuously transition between two primary swimming modes in response to a magnetic field. The tori also manipulated and transported other artificial swimmers, bimetallic nanorods, as well as passive colloidal particles. In the first behavioral mode, the tori accumulated and transported nanorods; in the second mode, nanorods aligned along the toriʼs self-generated streamlines. Our results indicate that such shape-programmed microswimmers have a potential to manipulate biological active matter, e.g. bacteria or cells., While there are many demonstrations of self-propelled synthetic particles, there are fewer realisations of multimode swimming for the same particle. Here the authors demonstrate two swimming behaviours in magnetically manipulated microtori and show that these can manipulate other active particles.

Carbon particulate matter (PM) is an undesirable aerosol pollutant formed from combustors such as power plants, refineries, and engines. The most common and effective method of mitigating PM emission is the capture of particulates using a filter, before particles are released into the atmosphere. In order to develop and improve advanced filtering materials, a better understanding is required of their chemical and mechanical behavior. We report on a novel phenomenon on the mobility and oxidation behavior of catalytic iron doped ceria nanoparticles in contact with mobile carbon black nanoparticles. The process is recorded by real time imaging within an environmental transmission electron microscope. In contrast to observations in previous studies, the separated ceria nanoparticles are found to actively move on the substrate and consume the connecting carbon particles one-by-one. The velocity of particle motion is correlated to the reaction temperature and oxygen pressure, both determining the reaction rate. Modeling using the Density Functional Theory suggests this motion is driven by the chemical bonding between the surface oxygen of the catalyst and the graphite layers of carbon black, initiated through the Van der Waals force between two types of nanoparticles.

In order to meet emissions and power requirements, modern engine design has evolved in complexity and control. The cost and time restraints of calibration and testing of various control strategies have made virtual testing environments increasingly popular. Using Hardware-in-the-Loop (HiL), Volvo Penta has built a virtual test rig named VIRTEC for efficient engine testing, using a model simulating a fully instrumented engine. This paper presents an innovative Artificial Neural Network (ANN) based model for engine simulations in HiL environment. The engine model, herein called Artificial Neural Network Engine (ANN-E), was built for D8-600 hp Volvo Penta engine, and directly implemented in the VIRTEC system. ANN-E uses a combination of feedforward and recursive ANNs, processing 7 actuator signals from the engine management system (EMS) to provide 30 output signals. To improve the accuracy in predicting exhaust emissions, the ANNs were arranged into two layers, such that engine temperature and pressure output signals and their average rate of change act as extra inputs for exhaust emission signals. The simulation results show that the ANN-E model accurately predicts engine performance, engine temperatures and pressures along the flow path, as well as exhaust emissions. In addition, the modular nature of ANN-E makes it possible for fast rebuild of the model if engine components are changed. Therefore, the layered modular ANN modeling approach represents a powerful tool for virtual engine testing and calibration optimization.

The present paper aims at developing an innovative procedure to create a one-dimensional (1D) real-time capable simulation model for a heavy-duty diesel engine. The novelty of this approach is the use of the top-level engine configuration, test cell measurement data, and manufacturer maps as opposite to common practice of utilizing a detailed 1D engine model. The objective is to facilitate effective model adjustments and hence further increase the application of Hardware-in-the-Loop (HiL) simulations in powertrain development. This work describes the development of Fast Running Model (FRM) in GT-SUITE simulation software. The cylinder and gas-path modeling and calibration are described in detail. The results for engine performance and exhaust emissions produced satisfactory agreement with both steady-state and transient experimental data. Therefore, the presented methodology shows a great potential for testing and validation of new control strategies in Engine Management System (EMS) and for optimizing engine performance using HiL systems. The model has been successfully used in powertrain testing and calibration in the VIRtual TEst Cell (VIRTEC) system at Volvo Penta.

A good combination of room-temperature and elevated temperature strength and ductility, good salt-spray corrosion resistance and excellent diecastability are frequently among the main characteristics considered when developing a new magnesium alloy. Unfortunately, much less effort has been expended developing wrought-stock alloys for high temperature applications. Extrudability and high temperature performance of wrought material becomes an important factor in an effort to develop new wrought alloys and processing technologies. This paper shows some results obtained from creep testing and studies of in-creep texture evolution, for several wrought magnesium alloys developed for use in elevated-temperature applications., Magnesium Technology 2011 - TMS 2011 Annual Meeting and Exhibition, 27 February 2011 through 3 March 2011, San Diego, CA