Academic literature on the topic 'Temporales Schließen'
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Journal articles on the topic "Temporales Schließen"
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Liu, Yun, Jesse Roll, Stephen Van Kooten, and Xinyan Deng. "Schlieren photography on freely flying hawkmoth." Biology Letters 14, no. 5 (May 2018): 20180198. http://dx.doi.org/10.1098/rsbl.2018.0198.
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The aerodynamic force on flying insects results from the vortical flow structures that vary both spatially and temporally throughout flight. Due to these complexities and the inherent difficulties in studying flying insects in a natural setting, a complete picture of the vortical flow has been difficult to obtain experimentally. In this paper, Schlieren , a widely used technique for highspeed flow visualization, was adapted to capture the vortex structures around freely flying hawkmoth ( Manduca ). Flow features such as leading-edge vortex, trailing-edge vortex, as well as the full vortex system in the wake were visualized directly. Quantification of the flow from the Schlieren images was then obtained by applying a physics-based optical flow method, extending the potential applications of the method to further studies of flying insects.
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Carnacho, J. F., D. E. Bliss, and S. M. Cameron. "Temporally resolved schlieren images of a laser-generated plasma." IEEE Transactions on Plasma Science 30, no. 1 (February 2002): 42–43. http://dx.doi.org/10.1109/tps.2002.1003914.
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Jagadeesh, Chetan, Erwin R. Gowree, Hesamaldin Jadidbonab, and Christopher J. Atkin. "On the temporal analysis of acoustic waves using schlieren imaging." Measurement 116 (February 2018): 507–13. http://dx.doi.org/10.1016/j.measurement.2017.11.018.
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Chitanont, N., K. Yatabe, K. Ishikawa, and Y. Oikawa. "Spatio-temporal filter bank for visualizing audible sound field by Schlieren method." Applied Acoustics 115 (January 2017): 109–20. http://dx.doi.org/10.1016/j.apacoust.2016.08.028.
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SUTHERLAND, BRUCE R., STUART B. DALZIEL, GRAHAM O. HUGHES, and P. F. LINDEN. "Visualization and measurement of internal waves by ‘synthetic schlieren’. Part 1. Vertically oscillating cylinder." Journal of Fluid Mechanics 390 (July 10, 1999): 93–126. http://dx.doi.org/10.1017/s0022112099005017.
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We present measurements of the density and velocity fields produced when an oscillating circular cylinder excites internal gravity waves in a stratified fluid. These measurements are obtained using a novel, non-intrusive optical technique suitable for determining the density fluctuation field in temporally evolving flows which are nominally two-dimensional. Although using the same basic principles as conventional methods, the technique uses digital image processing in lieu of large and expensive parabolic mirrors, thus allowing more flexibility and providing high sensitivity: perturbations of the order of 1% of the ambient density gradient may be detected. From the density gradient field and its time derivative it is possible to construct the perturbation fields of density and horizontal and vertical velocity. Thus, in principle, momentum and energy fluxes can be determined.In this paper we examine the structure and amplitude of internal gravity waves generated by a cylinder oscillating vertically at different frequencies and amplitudes, paying particular attention to the role of viscosity in determining the evolution of the waves. In qualitative agreement with theory, it is found that wave motions characterized by a bimodal displacement distribution close to the source are attenuated by viscosity and eventually undergo a transition to a unimodal displacement distribution further from the source. Close quantitative agreement is found when comparing our results with the theoretical ones of Hurley & Keady (1997). This demonstrates that the new experimental technique is capable of making accurate measurements and also lends support to analytic theories. However, theory predicts that the wave beams are narrower than observed, and the amplitude is significantly under-predicted for low-frequency waves. The discrepancy occurs in part because the theory neglects the presence of the viscous boundary layers surrounding the cylinder, and because it does not take into account the effects of wave attenuation resulting from nonlinear wave–wave interactions between the upward and downward propagating waves near the source.
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Sato, Takuso, Hidetaka Kojima, Osamu Ikeda, and Yoshiaki Odai. "Two-dimensional, optical temporal bandpass filter using four-wave mixing in a BSO crystal: dynamic schlieren imaging system." Applied Optics 26, no. 10 (May 15, 1987): 2016. http://dx.doi.org/10.1364/ao.26.002016.
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de Bruijne, Ad. "Living with Scripture, Living in a Democracy." European Journal of Theology 28, no. 2 (December 1, 2020): 124–35. http://dx.doi.org/10.5117/ejt2019.2.004.brui.
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RésuméLes chrétiens ont souvent fait face à des tensions entre leur identité chrétienne et leur statut de citoyens d’une démocratie. Ces tensions constituent une forme particulière de l’inévitable problème fondamental que rencontrent les chrétiens dans toute société au sein de laquelle ils vivent. À la suite de Saint Augustin, on peut exprimer cela en terme de la difficulté à articuler la double appartenance, à la cité de Dieu d’une part et à la « cité des hommes » de l’autre. En dépit de ces tensions, et en vertu de la providence divine, la participation des chrétiens peut aussi contribuer à des bénédictions temporaires pour la société à laquelle ils appartiennent. L’histoire du monde occidental en fournit bien des exemples, dont fait partie l’émergence même des démocraties. Dans le contexte postchrétien actuel, ces fruits historiques de l’influence chrétienne sont souvent dissociés de leurs racines et deviennent par conséquent instables, ou sont contrecarrés par des difficultés, voire des impasses. Ayant conservé leurs racines, les chrétiens peuvent souvent clarifier les choses et proposer des solutions. La contribution chrétienne peut s’avérer fructueuse, par exemple dans le contexte contemporain de l’opposition entre la version libérale de la démocratie de l’Europe occidentale et la version non libérale de l’Europe de l’Est. L’auteur conclut en mentionnant cinq points devant retenir l’attention concernant la participation de chrétiens à la vie d’une démocratie : il s’agit de rester attaché à l’Église qui constitue la communauté politique du Royaume à venir, de considérer l’identification à un organe politique terrestre comme demeurant secondaire, de promouvoir des activités au bénéfice de la société depuis le sein de l’Église, de tenir compte du fait que les objectifs moraux dans le contexte de la société doivent être différents de ceux que l’on adopte dans le contexte de l’Église, et de demeurer fidèle à un style de vie prophétique par la parole et les actes.SummaryChristians have traditionally experienced tensions between their Christian identity and their citizenship in a democracy. This tension is a special variant of the inevitable underlying classical challenge for Christians in all societies where they live. Following Augustine, this can be expressed as the challenge to combine the dual citizenships of the city of God and the ‘city of man’. Despite such tensions, under God’s providence the participation of Christians can also lead to temporary blessings for their societies. Western history provides many examples of this, the development of democracy being one of them. In the current post-Christian context these historical fruits of Christian influence have often become detached from their roots and therefore become unstable or burdened by difficulties and even deadlocks. Being still connected to that root, Christians can often provide clarification and contribute to solutions. This Christian contribution can be made fruitful, for example, in the contemporary clash between Western European liberal and Eastern European illiberal versions of democracy. The article concludes with five points of attention for Christian participation in a democracy: staying anchored in the Church as the political community of the future kingdom, considering earthly political identifications as secondary, developing public grass roots activities from within the Church, realising that moral aims in the context of society have to be different from those in the context of the Church, and remaining faithful to a prophetic lifestyle in word and deed.ZusammenfassungChristen erleben für gewöhnlich Spannungen zwischen ihrer Identität als Christ und als Staatsbürger in einer Demokratie. Diese Spannung stellt eine besondere Variante der unvermeidlichen klassischen Herausforderung dar, der Christen in jeglicher Gesellschaftsform begegnen. Gemäß Augustinus mag sich dies in der Schwierigkeit ausdrücken, die doppelte Staatsbürgerschaft in der ,,Stadt Gottes“ und der ,,Stadt der Menschen“ miteinander zu vereinen. Trotz derartiger Spannungen kann durch die Vorsehung Gottes auch der Einfluss von Christen zu vorübergehenden Segnungen für ihre Gesellschaft führen. Die westliche Geschichte liefert viele Beispiele hierfür, und die Entwicklung der Demokratie ist nur eines davon. Im gegenwärtigen nachchristlichen Kontext haben sich diese historisch gewachsenen Ergebnisse christlichen Einflusses häufig von ihren Wurzeln gelöst und wurden daher unstabil oder von Schwierigkeiten und sogar Blockaden überfrachtet. Solange Christen immer noch mit diesen Wurzeln verbunden sind, sind sie oftmals in der Lage, für eine Klärung von Situationen zu sorgen und zu Lösungen beizutragen. Dieser christliche Einfluss kann zum Beispiel im gegenwärtigen Konflikt zwischen liberalen westeuropäischen und illiberalen osteuropäischen Formen von Demokratie genutzt werden. Der Artikel schließt mit fünf Punkten, die für den Beitrag von Christen in einer Demokratie zu berücksichtigen sind: Christen bleiben in der Gemeinde als der politischen Gemeinschaft des künftigen Reiches Gottes verhaftet, säkulare politische Zuordnungen werden als sekundär betrachtet, öffentliche Basisaktivitäten werden aus der Gemeinde heraus entwickelt, in der Einsicht, dass sich ethische Zielsetzungen im gesellschaftlichen Kontext von jenen im Gemeindekontext unterscheiden müssen und unter der Voraussetzung, dass Christen einem prophetischen Lebensstil in Wort und Tat treu bleiben.
Dissertations / Theses on the topic "Temporales Schließen"
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Lattner, Andreas D. "Temporal pattern mining in dynamic environments /." Berlin : Akad. Verl.-Ges. Aka, 2007. http://deposit.d-nb.de/cgi-bin/dokserv?id=2995598&prov=M&dok_var=1&dok_ext=htm.
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Nowack, Kati. "About time." Doctoral thesis, Humboldt-Universität zu Berlin, Lebenswissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17535.
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Zeit ist ein fundamentaler Aspekt menschlichen Verhaltens. Während Untersuchungen bislang meist nur auf einem der drei Hauptaspekte der Zeit: Dauer, Zeitfolge und individuelle zeitliche Orientierung fokussierten, untersucht diese Dissertation Zusammenhänge zwischen der individuellen zeitlichen Orientierung und der Zeitfolge. Zeit ist nicht direkt wahrnehmbar, sondern an kognitive Abstraktionsprozesse gebunden. Diese benötigen kognitive Ressourcen und werden kognitiven Fähigkeiten beeinflusst. Daher wurden Zusammenhänge zwischen individueller zeitlicher Orientierung und allgemeinen kognitiven Fähigkeiten ebenfalls untersucht. Studie 1 analysiert, wie verschiedene Aspekte individueller zeitlicher Orientierung korreliert sind, und diese Korrelationen von Alter und Geschlecht beeinflusst sind. Studien 2 und 3a analysieren Zusammenhänge zwischen individueller zeitlicher Orientierung und der Zeitfolge. Studie 3b untersucht mittels einer geometrischen Analogieanforderung Korrelationen zwischen individueller zeitlicher Orientierung und höheren fluiden Intelligenzleistungen. Befunde zu Zeitperspektive-Chronotyp- Relationen sowie Zeithorizont-Chronotyp-Relationen werden berichtet, ebenso Zusammenhänge zwischen Zeitperspektive, Zeithorizont und der Zeitfolge. Ausgehend von diesen und früheren Befunden wird ein kognitives Modell vorgestellt, welches alle drei Aspekte psychologischer Zeit (Zeitdauer; Zeitfolge; individuelle zeitliche Orientierung) integriert. Ferner werden als Ergebnis der Studien Zusammenhänge zwischen der Zukunftsperspektive und fluider Intelligenz sowie Chronotyp und verbaler Intelligenz berichtet. Verhaltensdaten und psychophysiologische Daten (Pupillendilation) zeigen ferner Zusammenhänge zwischen individueller zeitlicher Orientierung, analogem Denken, exekutiven Funktionen und Konfliktverarbeitung. So scheinen Zukunftsperspektive und Morgentyp eng mit Konfliktverarbeitung verbunden, der Zeithorizont hingegen eng mit inhibierenden Kontrollprozessen.Time is a fundamental aspect of human experience. Whilst most research investigated major aspects of psychological time - time duration, time succession, individual temporal orientation - in isolation, this dissertation investigates interrelations between individual temporal orientation and time succession. Since psychological time is bound to cognitive abstraction processes that rely on cognitive resources and functions, interrelations between individual temporal orientation and cognitive capacities were also investigated. Study 1 explored how different levels of individuals’ temporal orientation may be interrelated, and how interrelations may be influenced by age and sex. Interrelations between individual temporal orientation and time succession were explored in a task predominantly requiring crystallized intelligence (Study 2) and in a semantic analogy task requiring crystallized and fluid intelligence (Study 3a). Study 3b investigated interrelations between individual temporal orientation and higher-level fluid intelligence measures by applying a geometric analogy task. Interrelations between time perspective and chronotype as well as between chronotype and temporal depth are reported. Further, both future time perspective and temporal depth are interrelated with time succession. A testable global working memory model of time perception integrating all three aspects of psychological time is proposed. Further, interrelations between individual temporal orientation and cognitive capacities are reported. Future time perspective was related to fluid intelligence, chronotype to verbal intelligence. Behavioral as well as pupillary data suggest that individual temporal orientation is related to analogical reasoning, executive functions and goal management. Whereas future time perspective and morningness appear interrelated with conflict detection, temporal depth appears interrelated with inhibitory control.
Book chapters on the topic "Temporales Schließen"
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Puppe, Frank. "Temporales Schließen." In Studienreihe Informatik, 65–71. Berlin, Heidelberg: Springer Berlin Heidelberg, 1991. http://dx.doi.org/10.1007/978-3-642-76621-3_9.
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Puppe, Frank. "Temporales Schließen." In Studienreihe Informatik, 65–71. Berlin, Heidelberg: Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-662-00706-8_9.
Full textConference papers on the topic "Temporales Schließen"
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Chitanont, Nachanant, Keita Yaginuma, Kohei Yatabe, and Yasuhiro Oikawa. "Visualization of sound field by means of Schlieren method with spatio-temporal filtering." In ICASSP 2015 - 2015 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP). IEEE, 2015. http://dx.doi.org/10.1109/icassp.2015.7178021.
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Lackner, Maximilian, Franz Winter, Soren Charareh, Kurt Iskra, Theo Neger, Herbert Kopecek, Ernst Wintner, Johann Klausner, and Gu¨nther Herdin. "Optical Diagnostics of Laser Ignition for Future Advanced Engines." In ASME 2004 Internal Combustion Engine Division Fall Technical Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/icef2004-0872.
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A laser-based system should be advantageous to a spark-plug based ignition system. Free choice of the ignition spot and precise timing constitute two major advantages. Multi point laser ignition could lead to higher efficiencies, and laser ignition as such is capable of igniting leaner mixtures than a spark plug, thereby decreasing thermal NOx and soot emissions. This paper is devoted to advances in optical diagnostics of laser ignition for future internal combustion engines. The focus of this paper is on diagnostics at high pressures, that is engine-like conditions. Laser ignition tests were performed with the fuels methane, hydrogen and biogas in static combustion cells with dimensions comparable to stationary engines. A Nd:YAG laser (5 ns pulse duration, wavelength 1064 nm, 1–20 mJ pulse energy) was used to ignite gaseous fuel/air mixtures at initial pressures of 1–3 MPa. Schlieren photography and laser-induced fluorescence (LIF) were used for optical diagnostics (flame kernel development, shock wave propagation). The lean burn characteristics were investigated. Schlieren photography was used to determine the velocity of the shock wave and to study the influence of the shock wave on temperature rise and energy loss. Using planar laser-induced fluorescence (PLIF), the spatial distribution of the combustion intermediates OH and formaldehyde were recorded. The temporally resolved imaging shows that the initial stages of the flame front evolution closely follows the turbulence and density fluctuations caused by the shock and pressure wave induced by the laser spark. In this paper, results from LIF spectroscopy and Schlieren photography are compared. Depending on the laser pulse energy and focus size, at later stages after the ignition the flame front propagation approaches the laminar burning regime and flame front speed decrease. Flame front break up at lean conditions indicates the limit of the ignitable mixture fraction when the speed due to spark-induced convection exceeds the flame propagation rate.
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Peraza, Jesús Enrique, Raul Payri, Jaime Gimeno, and Tim Bazyn. "Spray/wall interaction analysis on an ECN single-hole injector at diesel-like conditions through Schlieren visualization." In ILASS2017 - 28th European Conference on Liquid Atomization and Spray Systems. Valencia: Universitat Politècnica València, 2017. http://dx.doi.org/10.4995/ilass2017.2017.4709.
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To continuously improve CFD models which simulate spray evolution, breakup and evaporation mechanisms, it is helpful to validate them with results obtained by experimental research. In the present study, a mono-orifice target nozzle from Engine Combustion Network, referred to as Spray D, was investigated at conditions of spray-wall interaction, which actually is a real situation in internal combustion engines that is not frequently analyzed by visualization. A Photron SA-X2 high-speed camera was employed to record the vapor phase development of the spray in an inert atmosphere using a Schlieren imaging single-pass setup. The experiments show that the spreading of the spray along the wall has a behavior fairly similar to penetration at free-jet situations, especially regarding to its susceptibility to the operating conditions and its proportionality to the square root of time once the spray reaches a steady regime interacting with the wall. Furthermore, the spray film thickness was measured at three distances from the spray-wall impact point during the injection event, thereby characterizing that parameter both spatially and temporally. The tests were carried out in a constant pressure-flow facility able to reproduce pressure and temperature conditions, similar to those seen into a diesel engine. In order to observe the behavior of the spray colliding with a wall within this test rig, a system capable to being fitted into it and to holding a fused quartz wall at different injector tip-wall distances and impingement angle configurations, was designed and employed.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4709
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Singh, Dhruv, Atul Srivastava, and K. Muralidhar. "Tomographic Reconstruction of Unsteady Fields Using Proper Orthogonal Decomposition." In ASME 2008 Heat Transfer Summer Conference collocated with the Fluids Engineering, Energy Sustainability, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/ht2008-56443.
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An algorithm for the reconstruction of unsteady three dimensional concentration field from path-integrated data has been discussed. We propose the use of Proper Orthogonal Decomposition (Karhunen Loe´ve Expansion) to completely decouple the spatial and temporal components of the image sequence (projections) obtained from a typical experiment enabling the analysis of an asynchoronous time-dependent data set. We apply the algorithm to experimental data from a Laser Interferometric study of convection in a cylindrical annulus to capture transients that are invariably faster than the camera speed. The strength of the technique is demonstrated in the reconstruction of the flow field (related to concentration gradients) from model (simulated) Schlieren projections. Tomographic reconstruction based on Convolution Back Projection (CBP) has been coupled with Proper Orthogonal Decomposition to enable the reconstruction of unsteady concentration gradient field from asynchronous projections.
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Neumann, T., and H. Ermert. "4C-4 A New Designed Schlieren System for the Visualization of Ultrasonic Pulsed Wave Fields with High Spatial and Temporal Resolution." In 2006 IEEE Ultrasonics Symposium. IEEE, 2006. http://dx.doi.org/10.1109/ultsym.2006.74.
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Yamamoto, Atsunori, Ryuji Yamakita, Yojiro Ishino, and Norio Ohiwa. "Microscopic Approaches to Decomposition and Burning Processes of a Micro Plastic Resin Particle." In ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference collocated with the ASME 2007 InterPACK Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/ht2007-32169.
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From a fundamental and microscopic viewpoint to elucidate the possibility and availability of thermal recycling of wasted plastic resin, a series of heating processes of melting, thermal decomposition and burning of a spherical micro plastic resin particle having a diameter of about 200 μm are observed, when it is suddenly exposed to hot oxidizing combustion gas. Three ingenious devices are introduced; the first is a high-speed microscopic direct and schlieren system, the second is a pre-mixed mini-burner for abrupt heating, which is equipped with a pair of spark gaps at its exit and is discharged synchronously with the starting signal of high-speed camera, and the third is a single mini-puff generator, which enables to extinguish instantly all flames around the micro particle at an arbitrary assigned time after the spark ignition. Polyethylene terephthalate and polyethylene are used as two typical plastic resins. In this paper the dependency of internal and external appearances of residual plastic embers on the heating time and the initial plastic composition is optically analyzed, along with appearances of internal micro bubbling, micro jets and micro diffusion flames during abrupt heating. Based on temporal variations of the surface area of a micro plastic particle, the burning rate constant is also evaluated and compared with well-known volatile liquid fuels.
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Reggeti, Shawn, Allen Parker, C. Taber Wanstall, Ajay Agrawal, and Joshua Bittle. "Comparing Global Spray Combustion Characteristics and Local Shot-to-Shot Variations in a Reacting N-Heptane Spray." In ASME 2020 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/icef2020-3007.
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Abstract In support of efforts to develop improved models of turbulent spray behavior and combustion in diesel engines, experimental data and analysis must be obtained to guide and validate them. For RANS-based CFD modeling approaches it is important to have representative ensemble average experimental results. For models that provide high fidelity local details such as LES-based CFD simulations, it is desirable to have precise individual experiment results. Making comparisons however is a challenge as it is impossible to directly compare local parameters between a given experiment and LES simulation. An optically accessible constant pressure flow rig (CPFR) is utilized to capture injection and reaction behavior with three optical diagnostic techniques: rainbow schlieren deflectometry (RSD), OH* chemiluminescence (OH*), and two-color pyrometry (2CP). The benefit of these high-speed, simultaneous diagnostics is that local measurements can be made for every stage of a single injection event, observing both how much injections differ one from another, and also how such differences evolve temporally. The CPFR allows a sufficiently large number of repeated injection experiments to be performed for proper statistical analysis and ensemble convergence, while maintaining highly repeatable, nominally constant test conditions. Even given such stable conditions however, variations in local turbulent fuel-air mixing introduce a degree of variability which may manifest as significant differences in OH* and 2CP results. A statistical method is utilized to analyze the extent of this variability, and to identify superlative injections within the data set for discussion and analysis of shot-to-shot variation. Experimental measurements of characteristic parameters including liquid and vapor jet penetration, lift-off length, soot temperature and concentration, and turbulent flame speed, along with the shot-to-shot variability of each, are presented and discussed. While the results shown here can only postulate about the causation, the framework to characterize shot-to-shot variations could be leveraged to enable direct comparison with high-fidelity simulations without the need for averaging multiple realizations.
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Parajuli, Pradeep, Tyler Paschal, Mattias A. Turner, Eric L. Petersen, and Waruna D. Kulatilaka. "High-Speed Spectrally Resolved Imaging Studies of Spherically Expanding Natural Gas Flames Under Gas Turbine Operating Conditions." In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-91752.
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Abstract Natural gas is a major fuel source for many industrial and power-generation applications. The primary constituent of natural gas is methane (CH4), while smaller quantities of higher order hydrocarbons such as ethane (C2H6) and propane (C3H8) can also be present. Detailed understanding of natural gas combustion is important to obtain the highest possible combustion efficiency with minimal environmental impact in devices such as gas turbines and industrial furnaces. For a better understanding the combustion performance of natural gas, several important parameters to study are the flame temperature, heat release zone, flame front evolution, and laminar flame speed as a function of flame equivalence ratio. Spectrally and temporally resolved, high-speed chemiluminescence imaging can provide direct measurements of some of these parameters under controlled laboratory conditions. A series of experiments were performed on premixed methane/ethane-air flames at different equivalence ratios inside a closed flame speed vessel that allows the direct observation of the spherically expanding flame front. The vessel was filled with the mixtures of CH4 and C2H6 along with respective partial pressures of O2 and N2, to obtain the desired equivalence ratios at 1 atm initial pressure. A high-speed camera coupled with an image intensifier system was used to capture the chemiluminescence emitted by the excited hydroxyl (OH*) and methylidyne (CH*) radicals, which are two of the most important species present in the natural gas flames. The calculated laminar flame speeds for an 80/20 methane/ethane blend based on high-speed chemiluminescence images agreed well with the previously conducted Z-type schlieren imaging-based measurements. A high-pressure test, conducted at 5 atm initial pressure, produced wrinkles in the flame and decreased flame propagation rate. In comparison to the spherically expanding laminar flames, subsequent turbulent flame studies showed the sporadic nature of the flame resulting from multiple flame fronts that were evolved discontinuously and independently with the time. This paper documents some of the first results of quantitative spherical flame speed experiments using high-speed chemiluminescence imaging.
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Huang, Shuai, Tie Li, Chongmin Wu, Bin Wang, and Ming Zheng. "Effects of Various Discharge Strategies on Ignition of Lean Methane/Air Mixture." In ASME 2018 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/icef2018-9648.
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Ultra-lean burn with high turbulence has high potential for improving thermal efficiency and reducing NOx emissions in spark-ignition engines. Formation of initial flame kernel in high-turbulence flow by advanced ignition technologies is crucial for successful implementation of the ultra-lean burn concept. In this study, a four-coil ignition system is designed to enable temporally flexible discharge, including the single strike, multi-strike and continuous discharge with the discharge energy range from 100 to 300 mJ. The performance of the different discharge strategies on igniting the lean methane-air mixture is evaluated in an optically accessible constant volume vessel. The initial mixture pressure of 3.0 MPa and temperature of 388 K are set to simulate typical conditions near TDC (top dead center) of turbocharged large-bore natural gas engines. Both the flow and quiescent conditions around the spark plug are taken into account with and without gas flows in the vessel. The flame kernel formation and developing processes are captured by using the Schlieren imaging technique with a high-speed CMOS video camera, while evolution of both the voltage and current in the circuit are well monitored by the high-voltage probe and current clamp. With the continuous discharge ignition, the lean limit is remarkably extended in the case of the flow condition, while it is changed only slightly under the quiescent condition, compared with the other strategies. Analysis of the current and voltage waveforms shows that the continuous discharge strategy can enable a steadier and longer discharging period than the other strategies, regardless of conditions with and without gas flow. Besides, the continuous discharge strategy can accelerate the initial flame propagation compared with the other strategies. Once the flame kernel is successfully established, an increase in the discharge energy of single strike has no obvious effects on the flame development, but it is necessary for maintaining the lean limit. Although, in principle, the multi-strike discharge strategy can increase the ignition energy released to the mixture, the current waveform is prone to be interrupted with the discharge channel strongly distorted by the gas flow under the high-pressure condition. The flame propagation speed of the ultra-lean mixture is rather slow under the high ambient pressure quiescent condition compared with the high ambient pressure flow condition. Enhancement of turbulent flow in the mixture is very crucial for realizing the highly efficient and stable combustion of the lean mixture.
Reports on the topic "Temporales Schließen"
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Hart, Carl R., and Gregory W. Lyons. A Measurement System for the Study of Nonlinear Propagation Through Arrays of Scatterers. Engineer Research and Development Center (U.S.), November 2020. http://dx.doi.org/10.21079/11681/38621.
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Various experimental challenges exist in measuring the spatial and temporal field of a nonlinear acoustic pulse propagating through an array of scatterers. Probe interference and undesirable high-frequency response plague typical approaches with acoustic microphones, which are also limited to resolving the pressure field at a single position. Measurements made with optical methods do not have such drawbacks, and schlieren measurements are particularly well suited to measuring both the spatial and temporal evolution of nonlinear pulse propagation in an array of scatterers. Herein, a measurement system is described based on a z-type schlieren setup, which is suitable for measuring axisymmetric phenomena and visualizing weak shock propagation. In order to reduce directivity and initiate nearly spherically-symmetric propagation, laser induced breakdown serves as the source for the nonlinear pulse. A key component of the schlieren system is a standard schliere, which allows quantitative schlieren measurements to be performed. Sizing of the standard schliere is aided by generating estimates of the expected light refraction from the nonlinear pulse, by way of the forward Abel transform. Finally, considerations for experimental sequencing, image capture, and a reconfigurable rod array designed to minimize spurious wave interactions are specified. 15.