1,720,978 research outputs found
Numerical simulation of ion transport membrane reactors: Oxygen permeation and transport and fuel conversion
Full text linkIon transport membrane (ITM) based reactors have been suggested as a novel technology for several applications including fuel reforming and oxy-fuel combustion, which integrates air separation and fuel conversion while reducing complexity and the associated energy penalty. To utilize this technology more effectively, it is necessary to develop a better understanding of the fundamental processes of oxygen transport and fuel conversion in the immediate vicinity of the membrane. In this paper, a numerical model that spatially resolves the gas flow, transport and reactions is presented. The model incorporates detailed gas phase chemistry and transport. The model is used to express the oxygen permeation flux in terms of the oxygen concentrations at the membrane surface given data on the bulk concentration, which is necessary for cases when mass transfer limitations on the permeate side are important and for reactive flow modeling. The simulation results show the dependence of oxygen transport and fuel conversion on the geometry and flow parameters including the membrane temperature, feed and sweep gas flow, oxygen concentration in the feed and fuel concentration in the sweep gas.King Fahd University of Petroleum and MineralsKing Abdullah University of Science and Technology (KAUST) (grant number KSU-I1-010-01
NOₓ measurement and characterization in a gaseous fueled high-pressure direct-injection engine
No full textInternal combustion engines (ICE) produce emissions that are harmful to the environment and human health. Strict governmental regulations put in place to reduce these harmful emissions have driven engine advancements such as high-pressure direct-injection (HPDI) of natural gas (NG) technology developed by Westport Fuel Systems (WFS). Because NG has a lower flame temperature than diesel, nitrogen oxides NO and NO₂ (NOₓ), can be slightly reduced; nevertheless, they are still a problematic harmful emission in HPDI engines. The effects of exhaust gas recirculation (EGR), known to reduce in-cylinder temperatures and thus NOₓ emissions in diesel compression ignition (CI) engines, is not as well understood in HPDI engines. The intent of this research is to develop a better understanding of the sensitivity of NOₓ to the specific effects of EGR (in-cylinder temperature, oxygen concentration, and combustion duration) in HPDI engines. This was accomplished by identifying the limits of EGR as a NOₓ reduction strategy in HPDI engines using a dry EGR system on a single cylinder research engine (SCRE).
A baseline engine operating condition was developed to maintain a constant engine load of 12 bar gross indicated mean effective pressure (GIMEP), constant combustion phasing, and constant engine speed throughout an EGR sweep. To better understand the role oxygen concentration plays in NOₓ reduction, two equivalence ratios (φ) were tested and held constant throughout the EGR sweep: 0.6 and 0.7. The maximum EGR rate tested was ∼50% for each φ. Combustion instability (measured by the coefficient of variability (COV) of peak cylinder pressure (PCP) and GIMEP) increased by 2 and 3% at maximum EGR for φ = 0.6 and 0.7, respectively.
NOx emissions were reduced ∼80% up to 25% EGR. However, NOₓ sensitivity to the effects of EGR diminish significantly at rates above 35%. The inverse is also true for particulate matter (PM) and methane in that these emissions significantly increase at EGR rates above 35%. Lastly, a kinetics analysis of the effects of EGR in a simplified HPDI model was developed to identify that NOx is twice as sensitive to temperature changes as to changes in oxygen concentration changes.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat
Robust on-line engine exhaust methane measurements using wavelength modulation spectroscopy
No full textNatural gas (NG) is a promising alternative to diesel fuel for industrial engine applications. NG can potentially reduce emissions of CO₂, NOₓ, SOₓ, and particulate matter when compared to diesel. NG is more cost effective than diesel and there is existing infrastructure that makes it a more
feasible transitional fuel than other proposed alternatives. NG is comprised primarily of CH₄, which is a much more potent greenhouse gas than CO₂. If engine exhaust contains excessive quantities of CH₄, the potential environmental benefits of switching to NG cannot be realized. Diagnostic methods for characterizing CH₄ emissions in engine exhaust must, therefore, be implemented to develop informed emissions reduction strategies.
This work presents a wavelength modulation spectroscopy (WMS) system that was developed to characterize CH₄ emissions from NG engines. WMS is a laser based absorption spectroscopy method that uses specialized signal generation and data processing techniques to provide accurate measurements. In this work a new on-line processing method is shown to provide continuous CH₄ measurements in near-real time, for up to three hours, while requiring less than 0.01% of the memory that was consumed by previous processing methods. Additionally, a more advanced data processing method is shown to make measurements more robust. Improved calibration strategies are then presented, including two simulation-based methods that are demonstrated to work in the temperature range 30-90◦C. The simulations are shown to model WMS signals across the instrument’s dynamic range to within 5.4% or 1.7%, respectively, when compared to physical WMS measurements that were validated with a Fourier transform infrared spectrometer. Finally, the WMS system’s ability to measure in-use CH₄ emissions is demonstrated on three NG engines, including two engines on cargo ferries operated by an industry partner. Measurements of steady-state CH₄ emissions from the marine engines were used to characterize emissions as functions of engine loads. In-use emissions were characterized in 10% load increments, providing superior resolution than regulatory standards in industry. Findings from this work have contributed to historical emissions data for these engines and have quantified the effects of various CH₄ reduction strategies.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat
Combustion characteristics of micron-sized carbonaceous particles as energy carriers and fuel additives
No full textStudying single-particle combustion is essential for understanding the fundamental behavior of solid particles, whether used as energy carriers or fuel additives. Compared to biomass and coal, relatively small amounts of volatile matter, ash, and moisture are available in hydrochar, which makes this a desirable fuel for energy applications. Additionally, while graphene oxide-based particles have proven efficacy as fuel additives, their combustion behavior as particles remains unknown. In the present study, the flame characteristics of single micron-sized carbon-rich hydrochar particles are studied for the first time and compared against those of coal and arbutus bark (the wood feedstock from which hydrochar is derived). Moreover, the combustion behavior of graphene oxide and iron-decorated graphene oxide are examined for the first time. Arbutus bark undergoes hydrothermal carbonization to produce hydrochar. Iron nanoparticles are added to octadecylamine-functionalized graphene oxide. A burner is used to combust the particles in the products of a premixed flat flame. Five oxygen mole fractions of the combustion products (12% to 38%) are examined at a fixed adiabatic flame temperature of 1850 K. Simultaneous shadowgraphy and luminosity imaging are conducted to study the combustion of the particles and measure the ignition delay and combustion time. Arbutus bark particles ignite heterogeneously at high oxygen mole fractions, while hydrochar and coal particles feature an overlapping two-stage combustion process. Graphene oxide burns similarly to hydrochar, while iron-decorated graphene oxide disintegrates violently upon ignition. At low oxygen mole fractions, the arbutus bark particles burn following a sequential two-stage process, while hydrochar and coal demonstrate overlapping combustion stages. Iron-decorated graphene oxide exhibits fragmentation behavior for all conditions. Hydrothermal carbonization of arbutus bark creates pores on the hydrochar particles which are hypothesized to cause fragmentation, rocketing, and fast particle ignition. This carbonization also increases hydrochar combustion time, but it still burns faster than coal. Generally, the results show that hydrothermal carbonization can upgrade biomass into a more energy-dense fuel with improved combustion characteristics, making this net-zero fuel suitable for thermal energy applications. Decorating graphene oxide with iron decreases the ignition delay and significantly increased the burning rate, which are desirable characteristics of a fuel additive.Applied Science, Faculty ofEngineering, School of (Okanagan)Graduat
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Characterization of fuel injection and premixing in direct-injected dual-fuel natural gas engines using in-cylinder infrared absorption and high speed Schlieren imaging
No full textAnthropogenic climate change has become an increasingly dire challenge in recent decades motivating research on alternative fuel sources for heavy-duty engines. Compared with traditional diesel, natural gas (NG) offers an abundant, inexpensive alternative with potential for lower CO₂ emissions [1]. The main objectives of this work are to develop techniques to characterize gaseous fuel injection and premixing processes for pilot-ignited direct-injection NG (PIDING) engines, describe how these processes are affected by injection parameters and combustion chamber geometry and how they affect engine performance metrics such as emissions and efficiency. While the research presented here is focused on NG, the results are applicable to other lower carbon gaseous fuel sources such as H₂, biomethane, etc. with some adaptation. Gas premixing was investigated through local infrared absorption measurements of fuel concentration (using the LaVision internal combustion optical sensor (ICOS)) in an optically accessible research engine using high-pressure direct injection (HPDI) of NG and diesel. Engine measurements were performed with varying relative injection timing (RIT) across several previously identified combustion regimes [2]. High speed imaging techniques (Schlieren and background-oriented Schlieren (BOS)) were developed to describe the effects of combustion chamber geometry on gas injection and mixing. Techniques were developed using ICOS measurements to characterize the level of NG premixing at varying RIT. When NG jets impinged within the piston bowl, increasing NG premixing was shown to correlate with increasing gross indicated efficiency (ηi,g), increasing NOᵪ emissions and decreasing CO emissions while having a comparatively small impact on CH₄ emissions. The piston bowl shape was found to affect gas mixing, including whether jets are directed into the topland region above the piston bowl. When jets enter the topland, much of the jet was shown to become entrapped with large residence times leading to incomplete fuel oxidation. This in turn leads to higher emissions of CH₄ and reduced ηi,g relative to when jets impinge within the piston bowl. The experimental systems developed throughout this report offer a framework for further study of novel piston bowl designs and the effects of combustion chamber geometry on gas injection and mixing.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat
Characterizing regimes of stratified pilot-ignited direct-injection natural gas combustion in an optically-accessible engine
No full textHeavy-duty road transport is a significant contributor of greenhouse gases (GHG) and airborne pollutants, and remains challenging to decarbonize. Application of natural gas (NG) in pilot-ignited direct-injection NG (PIDING) engines has been proven to reduce emissions of pollutants and GHGs relative to conventional diesel engines. Recently, stratified-premixed NG combustion has been identified as a viable approach to further reduce PIDING pollutant emissions. However, there is insufficient experimental data on stratified-premixed PIDING combustion to guide its effective implementation. The objective of this work is to present a systematic evaluation of stratified-premixed PIDING combustion modes that span from fully-premixed to non-premixed conditions in terms of ignition, main combustion, and emissions behavior.
To address these objectives, a single-cylinder research engine facility was operated in conventional all-metal and optically-accessible configurations. The facility was upgraded with a custom-designed cylinder head and high-pressure diesel/NG fuel system to investigate PIDING combustion and apply multiple simultaneous in-cylinder diagnostics to supplement existing in-cylinder OH*-chemiluminescence and 700nm imaging. Quantitative feature extraction from single-cycle combustion images was enhanced by developing a novel image segmentation algorithm to improve characterization of cyclic variability of combustion processes.
Combined thermodynamic and optical analyses of injection timing, duration, and pressure effects for non-premixed PIDING combustion condition identified five distinct combustion processes, which were incorporated into an updated conceptual description of non-premixed PIDING combustion. Six regimes of stratified PIDING combustion distinguished by NG premixing time were identified and characterized for a wide range of injection pressures (14-22MPa) and equivalence ratios (0.47-0.71). Consistency of combustion regime characteristics with respect to injection pressure, equivalence ratio, and with the available literature provide confidence in the broad applicability of the identified combustion regimes (i.e. not engine-specific). NG mixture development, pilot-NG interactions, and reaction zone structure and growth rates were characterized using simultaneous in-cylinder imaging and local high-speed in-cylinder fuel concentration measurement. The conclusions of this work are summarized as a conceptual framework that parameterizes the spectrum of stratified PIDING combustion and highlights conditions where PIDING combustion performance may be improved. The key findings and novel analysis and experimental methods are broadly relevant to all pilot-ignited gaseous direct-injection combustion technologies and fuels.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat
Optical engine characterization of reference and novel fuels using a small-volume fuel system
No full textGlobal climate change drives research and implementation of low-carbon fuels. Engine combustion imaging offers insights to fuel performance and can be conducted early in the fuel development cycle due to relatively low consumption rates compared to those required for steady-state emissions testing. A flexible fueling system is used, implementing a hydraulic media separator for direct injection of up to 260 mL alternative fuel samples at pressures up to 1200 bar into a 2.0L, single-cylinder, optically accessible diesel engine. Optical engine studies provide understanding of injection spray phenomena, ignition delays, heat release rates, and soot propensity with qualitative analysis of reaction zone structure and propagation using high-speed imaging of natural luminosity and OH*-chemiluminescence. A local, three-colour pyrometry probe enables measurement of in-cylinder soot concentration and temperature. Two operating conditions were chosen to investigate various phenomena. The first operating condition is a low load single fuel injection that allows for consideration of injection and ignition behaviour in the mixing controlled combustion regime. The second operating condition uses a pilot and main fuel injection and is representative of a medium load condition using modern diesel injection strategies. Six fuels are characterized: diesel and n-heptane, reference fuels; canola and soybean methyl ester, commercial biodiesels; and graphene-oxide (GO) doped diesel and a blend of upgraded bio-oil (UBO) from fast pyrolysis of pine biomass with diesel, novel fuels. Fuel properties were measured using ASTM standards for energy content, viscosity, elemental analysis, and moisture content. The UBO diesel blend demonstrates a 7% reduction in ignition delay and 25% reduction in in-cylinder soot concentration relative to neat diesel. The addition of 10ppm GO to diesel did not affect fuel performance.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat
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