Investigation of Soot Formation by Optical Diagnostics: From Precursor Measurements to 3D Particle Sizing PDF Download
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Author: Florian Jakob Bauer
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Languages : en
Pages : 0
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Author: Florian Jakob Bauer
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Languages : en
Pages : 0
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Author: Barbara Menkiel
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Languages : en
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This study is dedicated to investigation of soot formed during combustion in diesel engine. Measurements were performed in a high speed direct injection optical diesel engine. Initially soot particle size, size distribution and soot volume fraction were investigated using time resolved laser induced incandescence (TR-LII) technique. For this study standard diesel fuel was used and measurements were performed for various injection timing and two different engine loads. Investigation showed that TR-LII is a powerful tool that can be used for characterization of in-cylinder soot in the engines. Subsequently TR-LII technique was developed to measure in-cylinder soot in two dimensional plane (planar laser induced incandescence PLII) and technique was combined with high speed imaging to investigate soot processes for ultra-low sulfur diesel (ULSD) and bio-fuel (RME). Two injection strategies of single and double injection were applied during these measurements. A high speed imaging technique was used to study the soot formation and oxidation during the combustion process within the cylinder and PLII was applied later in the stroke to study qualitatively the relative amount of un-oxidised soot that was left in the combustion chamber. In addition to PLII, TR-LII technique was used simultaneously to explore crank angle resolved variation of primary soot particle size and their size distribution during the expansion stroke. The same measurements were repeated for fuels with different composition investigating the relationship between the fuel properties and soot emission. Finally mathematical model for soot particle size and distribution width was modified by introducing assumption of multi-lognormal in-cylinder soot particle size distribution.
Author: Armin Veshkini
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Languages : en
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Author: Dale Reif Tree
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Languages : en
Pages : 452
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Author: Madhu Singh
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Languages : en
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The negative health implications associated with combustion produced soot demand identification of contributing sources, quantification and characterization of their emissions to assess its impact, and control to minimize the imposed hazard. Distinguishing different sources of soot from engines and combustors is challenging, given the morphological and chemical similarity of the emitted soot. Leaner combustion conditions and tighter emission limits challenge traditional filter-based measurements for soot mass. Meanwhile, current after-treatment particulate control strategies are based on regeneration, i.e., soot oxidation which in turn depends upon soot nanostructure and composition (such as in a diesel particulate filter). Presently, effects on human health associated with soot exposure are largely correlative, while controlled lab studies predominantly use varied washings or extracts of soot, but rarely the actual particulate. Given the intertwined nature of these topics this dissertation addresses each in an integrated approach. Laser-induced incandescence (LII) is used to determine soot concentration while Time-resolved LII (TiRe-LII) can be used to estimate soot primary particle size largely by using available and appropriate models. The use of laser diagnostics has been used to experimentally demonstrate prevailing inconsistencies between experimentally measured and model-derived particle diameter values. Discrepancies have been attributed (a) to the empiricism associated with evaluating modeling variables and (b) to the lack of proper accountability of the changes in soot nanostructure upon heating with a pulsed laser. This work uses an experimental approach coupled with microscopy to (a) test the robustness of existing LII models and (b) inform existing models of experimental observations so that these can be accounted for in future models. Specifically, the contribution of changing soot nanostructure on laser heating is known and is shown here again with transmission electron microscopy (TEM). However, the change in soots optical properties because of an altered nanostructure remains unclear. Optical properties change when soot is laser-heated, and this alteration of optical properties upon laser heat treatment has been shown in this work experimentally, by using UV-Vis spectroscopy. Also, the effect of the degree of aggregation on the soots cooling profile is highlighted. This work demonstrates that different degrees of aggregation results in a shift of the time-temperature-history (TTH), thereby resulting in erroneous particle size predictions, which are calculated from the materials TTH. Unfortunately, most models assume point-contacting spheres and aggregation remains unaccounted for. The effect of the thermal accommodation coefficient is similar in that a small change in the value of this mathematical parameter significantly alters particle cooling as simulated here by an open-access simulator, indicating the need to exercise caution when assigning a value to this parameter in the model. While the change in soot nanostructure as a consequence of laser annealing complicates the interpretation from LII measurements, laser heating of soot can reciprocally be used to purposefully study the evolution in soot nanostructure as a function of its chemistry. Soot chemistry varies with its combustion environment, with fuel and combustion conditions specific to each source. Thus, by association, the evolution of soot nanostructure observed upon laser heat treatment can be correlated to its fuel origins and combustion origins, potentially identifying its formation source. Fundamentally, the presence of oxygen in nascent soot is identified here as a key compositional parameter. The increase in oxygen content of the fuel, as diesel is blended with increased proportions of biofuel, is correlated to increased oxygen content in the soot that is generated by the respective fuel. In other words, fuel with a higher oxygen content generates soot which also has oxygen content relatively higher than soot generated by fuel with low oxygen content. This work shows that oxygen dictates the evolution of soot nanostructure when it escapes the material upon laser heat treatment. When laser heated, the nanostructure of soot with a higher oxygen content evolves as hollow-shell like structures while nanostructure of soot with a low oxygen content evolves to show a ribbon-like interior. This divergence in soot nanostructure based on the oxygen content of nascent soot, which in turn is shown to be a function of the fuel composition, could be used to identify the source that generated the soot sample studied. Given the lack of availability of authentic soot samples, the combination of laser heat treatment and TEM of soot to identify fuel or source is powerful when sample quantities are in the range of less than a few nanograms. Being able to identify sources and their contributions using laser derivatization of soot as a diagnostic can help optimize new or existing control measures to reduce the concentration of atmospheric soot. For instance, diesel particulate filters (DPFs) are used to reduce diesel soot emissions. Effective protocols for DPF operation can be developed by understanding soot nanostructure changes as captured soot is oxidized during passive and active DPF regeneration. Typically, O2, NO2 or a combination of the two oxidants are encountered during DPF regeneration. In this work, soot nanostructure has been shown to vary with the order of oxidants to which it is exposed, a significant finding towards optimizing DPF filter regeneration protocols. The study has been performed on authentic diesel soot in a thermogravimetric analyzer under conditions mimicking active and passive regeneration in a DPF. To validate observations with diesel soot, three carbon blacks with varying nanostructure are also subjected to oxidation by O2 and NO2. The intriguing result is that order of oxidation matters, i.e., the oxidation rates are dependent upon nanostructure changes in response to oxidation by O2 alone, or O2 with NO2.Prolonged exposure to particulate matter causes unwanted ill-health, lung dysfunctions, and breathing problems. Most toxicity studies are done using a washing, or an extract of the organic fraction of soot and cells are exposed to this extract. This work tests the adverse effect of soot on human (male) lung cells when these are exposed to surrogate soot as is, i.e., structure and chemistry intact to mimic real-time exposure conditions. The impact of soot chemistry and the presence of acidic functional groups on lung epithelial cells for varying exposure times is demonstrated in our collaborative work with the College of Medicine at Penn State, Hershey, PA. Soot chemistry is shown to directly and adversely impact cell viability and mRNA expressions of the IL-1B and IL-6 cytokines as well as mRNA expression of the TLR4 protein. Specifically, cell viability was shown to reduce significantly after 6- and 24-hours of exposure to carboxylic groups on the soot, thereby demonstrating the health impact of soot surface chemistry in comparison to extracts.In summary, soot measurement, its extensive characterization to identify source contributions and develop practically applicable control strategies has a direct implication on our health and surroundings and can aid in promoting a healthy living environment.
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Languages : en
Pages : 16
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In order to provide the scientific foundation to enable technology breakthroughs in transportation fuel, it is important to develop a combustion modeling capability to optimize the operation and design of evolving fuels in advanced engines for transportation applications. The goal of this proposal is to develop a validated predictive model to describe the chemical composition of soot nanoparticles in premixed and diffusion flames. Atomistic studies in conjunction with state-of-the-art experiments are the distinguishing characteristics of this unique interdisciplinary effort. The modeling effort has been conducted at the University of Michigan by Prof. A. Violi. The experimental work has entailed a series of studies using different techniques to analyze gas-phase soot precursor chemistry and soot particle production in premixed and diffusion flames. Measurements have provided spatial distributions of polycyclic aromatic hydrocarbons and other gas-phase species and size and composition of incipient soot nanoparticles for comparison with model results. The experimental team includes Dr. N. Hansen and H. Michelsen at Sandia National Labs' Combustion Research Facility, and Dr. K. Wilson as collaborator at Lawrence Berkeley National Lab's Advanced Light Source. Our results show that the chemical and physical properties of nanoparticles affect the coagulation behavior in soot formation, and our results on an experimentally validated, predictive model for the chemical composition of soot nanoparticles will not only enhance our understanding of soot formation since but will also allow the prediction of particle size distributions under combustion conditions. These results provide a novel description of soot formation based on physical and chemical properties of the particles for use in the next generation of soot models and an enhanced capability for facilitating the design of alternative fuels and the engines they will power.
Author: Jaclyn Dunn
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Languages : en
Pages : 0
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This study applies the techniques of laser induced incandescence (LII) and laser induced fluorescence (LIF) to investigate laminar sooting flames of premixed ethylene air. The approach involves using three different excitation wavelengths, together with temporally and spectrally resolved detection, generating a rich dataset concerning the formation of soot and polycyclic aromatic hydrocarbons (PAHs). Both prompt and delayed detection are used to perform LII when exciting with short wavelengths, both with issues involved. Delayed detection gives an underestimation of soot volume fraction at low heights in the flame, as a result of particle size effects. Prompt detection gives overestimation of soot volume fraction due to fluorescence in the measurement volume. It is shown that care must be taken with either method and through evaluation of the associated errors this study shows delayed detection provides a more accurate measure of soot volume fraction. The ability to obtain the fluorescence signals over a range of heights above burner and stoichiometries is demonstrated. The approach relies on heating the soot particles equivalently with three excitation wavelengths so the LII contribution to the signals can be subtracted, leaving only fluorescence. Fluorescence profiles obtained show similar features to those seen in the literature for invasive measurements, including a reduction in the fluorescence signal generated by 283 nm excitation at intermediate heights above the burner surface followed by a re-increase. Although the data do not allow species-selective measurements of PAHs, these in-situ measurements allow inferences to be drawn about changing concentration of different size classes of these precursors to soot formation. Finally the method of obtaining subtracting the LII contribution to signals was used to obtain fluorescence spectra both for 283 nm and 532 nm excitation. This showed the possibility that fluorescence can yield useful information that it is otherwise impossible to obtain in-situ under sooting conditions.
Author: Meghdad Saffaripour
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Languages : en
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Author: Kevin Wan
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Languages : en
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Increasingly strict regulations on NOx and soot emissions from combustion systems drives the need to develop strategies to reduce them. One such strategy is to reduce them at the source. A basic understanding about how they form and how to properly characterize them is critical to improved combustion system design. In this dissertation, NOx formation is studied experimentally and numerically for a typical jet fuel. Characterization of soot by transmission electron microscopy and optical diagnostics is reevaluated here. The dissertation presents findings with new implications on the suitability on the use of these techniques to study soot. Reliable NOx data in stagnation flames of a typical jet fuel is presented here. The predictive capability for NOx is tested by combining a HyChem model with a NOx submodel. NOx formation is measured in premixed stagnation flames of methane, ethylene and Jet A (POSF10325). The experimental data and model predictions show reasonably good agreement. However, the model appears to underpredict NOx formation in the fuel-rich Jet A flames. Additional prompt NO reaction pathways not yet accounted for may play a role in flames of large hydrocarbons. Transmission electron microscopy imaging of nascent soot was carried out to observe and quantify the annealing of soot samples under continuous irradiation of the high-energy electron beam. Soot samples are imaged in 2 minute intervals over a duration of 16 minutes. The structural transformation is visually unambiguous. The sensitivity of the fringe properties to the apparent changes in the nanostructures imaged is examined. The difficulties in quantifying soot composition through TEM are further illustrated by analyzing simulated images of molecular-dynamics generated particles. Together, the results highlight the difficulties in using electron microscopy to reliably quantify structural properties for nascent soot particles. Quantum confinement is examined in the ionization energy and optical band gap of soot nanoparticles over the range of 4-23 nm in volume median diameter. The results reveal that soot nanoparticles behave like an indirect band gap material due to the electronic structure of the aromatic molecules comprising the soot nanoparticles. Both the ionization energy and optical band gap are found to follow the quantum confinement effect closely. Cyclic voltammetry measurements and density functional theory calculations provide additional support for the quantum dot behavior observed. A model for the refractive index of nascent soot particles is proposed over the wavelength range of 185 - 1400 nm. The refractive index of soot is shown to depend on the primary particle size for the first time. The refractive indices evaluated for large soot particles are in close agreement with literature values in the visible spectrum. The imaginary component is strongly sensitive to the particle size, deviating significantly from literature values at wavelengths > 700 nm and particle sizes ~ 15 nm in diameter. This highlights the need to account for the size effect in the refractive index in optical diagnostics of soot in flames, with implications on earlier extinction and scattering measurements of flame soot during the early stage of soot growth.
Author: H Zhao
Publisher: Elsevier
ISBN: 1845697456
Category : Technology & Engineering
Languages : en
Pages : 761
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Volume 2 of the two-volume set Advanced direct injection combustion engine technologies and development investigates diesel DI combustion engines, which despite their commercial success are facing ever more stringent emission legislation worldwide. Direct injection diesel engines are generally more efficient and cleaner than indirect injection engines and as fuel prices continue to rise DI engines are expected to gain in popularity for automotive applications. Two exclusive sections examine light-duty and heavy-duty diesel engines. Fuel injection systems and after treatment systems for DI diesel engines are discussed. The final section addresses exhaust emission control strategies, including combustion diagnostics and modelling, drawing on reputable diesel combustion system research and development. Investigates how HSDI and DI engines can meet ever more stringent emission legislation Examines technologies for both light-duty and heavy-duty diesel engines Discusses exhaust emission control strategies, combustion diagnostics and modelling
