Download or read book A Computational Study of Laminar Flame Propagation Into Mixtures with Non zero Reaction Progress in Engine Conditions written by and published by . This book was released on 2019 with total page 210 pages. Available in PDF, EPUB and Kindle. Book excerpt: Flame speed data reported in most literature are acquired in conventional apparatus such as the spherical combusion bomb and counter flow burner, and are limited to atmospheric pressure and ambient or slightly elevated unburnt temperatures. As such, these data bear little relevance to internal combustion engines and gas turbines, which operate under typical pressures of 10-50 bar and unburnt temperature up to 900K or higher. These elevated temperatures and pressures not only modify dominant flame chemistry, but more importantly, they inevitably facilitate pre-ignition reactions and hence can change the upstream thermodynamic and chemical conditions of a regular hot flame leading to modified flame properties. This study focuses on how auto-ignition chemistry affects flame propagation, especially in the negative-temperature coefficient (NTC) regime, where dimethyl ether (DME), n-heptane and iso-octane are chosen for study as typical fuels exhibiting low temperature chemistry (LTC). The structure of this thesis consists of the introduction of the combustion, the governing equations in thermodynamics and chemical reactions as well as the general structure of the flame. Then, the typicl experimental configuration exploited in the measurement of laminar flame speed is introduced, which is followed by the manifestation of the low temperature chemistry and the gap between the reality and the experimental understandings. Finally, the simulation results of laminar flame speed at constant pressure condition and HCCI engine condition are presented and discussed respectively. The computation of laminar flame speed of lean and stoichiometric mixtures of fuel/air was performed at different ignition reaction progress, by selecting the thermal chemical states corresponding to different residence times during auto-ignition as the flame upstream condition. Using scaling and budget analysis, it is shown that a well-defined flame speed for such a partially reactive mixture in the classical diffusion-reaction limit could still be feasible in the appropriate computational domain, especially with a sufficiently reduced induction length. The comparison of flame speed against different types of progress variables indicates a nearly linear relationship between the flame speed and progress variables based on the fuel mass fraction and temperature. The overall effect of the cool-flame reformation has been studied by comparing the flame speed of the initial mixture and that of the instantaneous mixture under the same thermodynamic conditions. It is found that the enhanced propagation is shown to be largely a thermodynamic effect, while chemistry nevertheless plays an overall retarding role. Sensitivity analysis has been performed to identify the key species which most influence flame propagation at different reaction progress. A general scheme of simplified mixture was constructed to describe flame propagation in a partially reactive mixture, for both lean and stoichiometric, as well as high pressures conditions. The findings and general simplified mixture scheme are validated in HCCI engine conditions.
Download or read book Turbulent Premixed Flames written by Nedunchezhian Swaminathan and published by Cambridge University Press. This book was released on 2011-04-25 with total page 447 pages. Available in PDF, EPUB and Kindle. Book excerpt: A work on turbulent premixed combustion is important because of increased concern about the environmental impact of combustion and the search for new combustion concepts and technologies. An improved understanding of lean fuel turbulent premixed flames must play a central role in the fundamental science of these new concepts. Lean premixed flames have the potential to offer ultra-low emission levels, but they are notoriously susceptible to combustion oscillations. Thus, sophisticated control measures are inevitably required. The editors' intent is to set out the modeling aspects in the field of turbulent premixed combustion. Good progress has been made on this topic, and this cohesive volume contains contributions from international experts on various subtopics of the lean premixed flame problem.
Download or read book An Experimental and Computational Study on the Propagation and Kinetic Structure of Laminar Premixed Flames written by Fokion Egolfopoulos and published by . This book was released on 1990 with total page 430 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Methods in Laminar Flame Propagation written by Norbert Peters and published by Springer-Verlag. This book was released on 2013-11-21 with total page 211 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Laminar Flame Propagation in Mixtures with Compositional Stratification at Small Length Scales written by David P. Schmidt and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The behavior and structure of laminar hydrocarbon flames which propagate parallel to the direction of a periodic gradient of mixture composition was studied both experimentally, using a specially designed burner, and computationally, using a planar numerical model. The variations in local mixture composition led to the formation of wrinkled flames, the structure of which were dependent on both chemical and physical parameters of the particular flame configuration. A qualitative study using chemiluminescence imaging of stratified methane and propane flames was conducted to characterize their response to variations in overall mixture composition, strength and length scale of the stratification, and flow field velocity. A two-dimensional numerical study was performed to assess the abilities of reduced global kinetic models to predict the behavior of stratified flames in comparison to computations performed using detailed mechanisms. It was observed that the reduced kinetic models display a lower limit of stratification length scale, which is on the order of the laminar flame thickness, below which accurate prediction of flame behavior is no longer possible. Under these conditions, the computed flames were observed to undergo a deformation which was much larger than the wrinkling imposed by the compositional variation, and was unsteady in time. Further analysis of these deformed flames suggested that a potential cause of this behavior was a failure of the reduced kinetics to capture the increase in local reaction rate attributed to stratification, and the inability of the driving reactions to counterbalance the incoming mass flux of fuel led to destabilization of the flame front. A preliminary analysis of the local stretch rates of the wrinkled flames was also conducted, and it was observed that even with a uniform incoming flow field, variations in mixture composition were capable of stretching the flames. The stretch behavior observed was one of alternating flame stretch and flame compression, which reached very large magnitudes over short distances.
Download or read book Energy Research Abstracts written by and published by . This book was released on 1991 with total page 622 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Turbulent Combustion written by Norbert Peters and published by Cambridge University Press. This book was released on 2000-08-15 with total page 322 pages. Available in PDF, EPUB and Kindle. Book excerpt: The combustion of fossil fuels remains a key technology for the foreseeable future. It is therefore important that we understand the mechanisms of combustion and, in particular, the role of turbulence within this process. Combustion always takes place within a turbulent flow field for two reasons: turbulence increases the mixing process and enhances combustion, but at the same time combustion releases heat which generates flow instability through buoyancy, thus enhancing the transition to turbulence. The four chapters of this book present a thorough introduction to the field of turbulent combustion. After an overview of modeling approaches, the three remaining chapters consider the three distinct cases of premixed, non-premixed, and partially premixed combustion, respectively. This book will be of value to researchers and students of engineering and applied mathematics by demonstrating the current theories of turbulent combustion within a unified presentation of the field.
Download or read book A Computational Study of Auto ignition and Flame Propagation in Stratified Mixtures Relevant to Modern Engines written by Ramanan Sankaran and published by . This book was released on 2004 with total page 314 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Flame Propagation of Jet A 1 Fuel and Its Surrogates written by Bradley Denman and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "The laminar flame speed is an essential flame parameter for both chemical kinetic mechanism validation and turbulent combustion studies. Kerosene-derived jet fuel flame speeds, however, are largely unknown and due to complex composition of the fuels themselves they cannot be modelled numerically. To overcome this limitation surrogate fuels and blends are used to reproduce the same flame speed of amore complex mixture. To accomplish this for aviation fuel, a database is created of four potential jet fuel surrogate components for laminar flame speed. The neat hydrocarbon surrogates investigated are n-dodecane and n-decane, methylcyclohex-ane, and toluene, which represent the alkane, cycloalkane, and aromatic components of conventional aviation fuel, respectively. Several blends of these surrogate fuels are tested experimentally and numerically to validate the effect of blend composition on flame speed. The database is then used to develop a blend to match the flame speeds of a commercial aviation fuel, Jet A-1. Unlike previous investigations of flame propagation, in this study, numerical simulations are directly compared to velocity profile measurements in laminar stagnation flames to extrapolate to a condition of zero flame stretch. Numerical simulations of each experiment are obtained using the CHEMKIN-PRO software package and the JetSurF 2.0 mechanism with accurate specification of all necessary boundary conditions from experimental measurements. The advantage of this technique is that the extrapolation to the unstretched condition is independent of the how well the mechanism predicts reactivity. Therefore, JetSurF 2.0 was simultaneously validated for each of the surrogate fuels and blends in a previously unused manner. The mechanism showed relatively good agreement for the n-alkane and cycloalkane fuels for which it was optimized for, while consistently under predicted the reactivity of toluene. The compiled database of jet fuel surrogate components allowed for five different potential surrogate mixtures to be developed. Experimental results of these blends suggest that although jet fuel is a very complex mixture a simple surrogate mixture consisting of 73% n-decane and 27% toluene byvolume appropriately matches the flame speed of Jet A-1. Numerical results using JetSurF 2.0 suggest that a 63% n-decane and 37% toluene by volume blend is the most appropriate surrogate and this was used to extrapolate the experimental JetA-1 results and determine its laminar flame speed." --
Download or read book Synthesis Gas Combustion written by Tim Lieuwen and published by CRC Press. This book was released on 2009-09-16 with total page 388 pages. Available in PDF, EPUB and Kindle. Book excerpt: Coal, still used to generate more than half of the electric power in the U.S., will likely be part of any future global energy plan. But this finite resource is also responsible for 80 percent of the CO2 emissions from power production, and its continued use will require improved processing techniques that are less damaging to the environment and l
Download or read book Encyclopedia of Automotive Engineering written by and published by John Wiley & Sons. This book was released on 2015-03-23 with total page 3888 pages. Available in PDF, EPUB and Kindle. Book excerpt: Erstmals eine umfassende und einheitliche Wissensbasis und Grundlage für weiterführende Studien und Forschung im Bereich der Automobiltechnik. Die Encyclopedia of Automotive Engineering ist die erste umfassende und einheitliche Wissensbasis dieses Fachgebiets und legt den Grundstein für weitere Studien und tiefgreifende Forschung. Weitreichende Querverweise und Suchfunktionen ermöglichen erstmals den zentralen Zugriff auf Detailinformationen zu bewährten Branchenstandards und -verfahren. Zusammenhängende Konzepte und Techniken aus Spezialbereichen lassen sich so einfacher verstehen. Neben traditionellen Themen des Fachgebiets beschäftigt sich diese Enzyklopädie auch mit "grünen" Technologien, dem Übergang von der Mechanik zur Elektronik und den Möglichkeiten zur Herstellung sicherer, effizienterer Fahrzeuge unter weltweit unterschiedlichen wirtschaftlichen Rahmenbedingungen. Das Referenzwerk behandelt neun Hauptbereiche: (1) Motoren: Grundlagen; (2) Motoren: Design; (3) Hybrid- und Elektroantriebe; (4) Getriebe- und Antriebssysteme; (5) Chassis-Systeme; (6) Elektrische und elektronische Systeme; (7) Karosserie-Design; (8) Materialien und Fertigung; (9) Telematik. - Zuverlässige Darstellung einer Vielzahl von Spezialthemen aus dem Bereich der Automobiltechnik. - Zugängliches Nachschlagewerk für Jungingenieure und Studenten, die die technologischen Grundlagen besser verstehen und ihre Kenntnisse erweitern möchten. - Wertvolle Verweise auf Detailinformationen und Forschungsergebnisse aus der technischen Literatur. - Entwickelt in Zusammenarbeit mit der FISITA, der Dachorganisation nationaler Automobil-Ingenieur-Verbände aus 37 Ländern und Vertretung von über 185.000 Ingenieuren aus der Branche. - Erhältlich als stets aktuelle Online-Ressource mit umfassenden Suchfunktionen oder als Print-Ausgabe in sechs Bänden mit über 4.000 Seiten. Ein wichtiges Nachschlagewerk für Bibliotheken und Informationszentren in der Industrie, bei Forschungs- und Schulungseinrichtungen, Fachgesellschaften, Regierungsbehörden und allen Ingenieurstudiengängen. Richtet sich an Fachingenieure und Techniker aus der Industrie, Studenten höherer Semester und Studienabsolventen, Forscher, Dozenten und Ausbilder, Branchenanalysen und Forscher.
Download or read book Symposium on Turbulent Shear Flows written by and published by . This book was released on with total page 524 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1992 with total page 348 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Reduced Chemical Kinetic Models for Real Fuels and Computational Flame Diagnostics of Premixed Combustion written by Ji-Woong Park and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation investigates different approaches to developing efficient yet accurate real-fuel chemistry for multi-dimensional computational fluid dynamics (CFD) simulations and computational flame diagnostics for premixed combustion. First, reduced kinetic models of real fuels are systematically developed based on detailed mechanisms with a hybrid chemistry (HyChem) approach. A two-stage reduction is utilized including a directed relation graph (DRG) and sensitivity analysis followed by linearized quasi-steady state approximation (LQSSA). Comprehensive validations are performed in homogeneous and diffusive systems over wide parameter ranges, showing good agreement between reduced and detailed mechanisms. The second approach focuses on spark ignition (SI) engine applications where laminar flame speed (LFS) plays a crucial role. Typically, in SI-engines, combustion starts at relatively high pressure and temperature. However, most chemical mechanisms are not validated in LFS at such conditions due to the lack of experimental data. The tailoring methodology of a chemical mechanism is proposed to improve prediction of LFS at engine-relevant conditions. Rate coefficients of the selected reactions important to LFS are identified through sensitivity analysis and adjusted within their uncertainty limits to match calculated LFS to experiment-based empirical correlation. The developed tailored mechanism is utilized in 3D SI-engine simulations and improved predictions are observed compared with experimental data. Lastly, a computational flame diagnostic tool to identify the extinction state of premixed flames is developed based on the chemical explosive mode (CEM) analysis (CEMA). Counterflow twin premixed flames show two different extinction modes with increasing stretch due to reaction incompleteness (Mode I) and preferential diffusion effect (Mode II). In Mode I, increasing stretch pushes the flame front, identified as zero-crossing of CEM eigenvalue, toward the stagnation plane such that twin flames merge and form a hot spot approaching extinction. The extinction Mode I can be identified by the zero-crossing of the CEM eigenvalue at the stagnation plane. For Mode II, the extinction occurs away from the stagnation plane due to the combined effect of stretch and preferential diffusion. A new criterion is constructed to quantify the contribution of back-diffusion of heat and radicals to the CEM in the preheat zone. The CEMA-based criteria are then validated in wide ranges of operating conditions covering lean to rich mixtures, elevated inlet temperature and pressure conditions, and small to large real-fuels, showing that it can be used as a leading order indicator for premixed flame extinction.
Download or read book Theoretical and Numerical Combustion written by Thierry Poinsot and published by R.T. Edwards, Inc.. This book was released on 2005 with total page 544 pages. Available in PDF, EPUB and Kindle. Book excerpt: Introducing numerical techniques for combustion, this textbook describes both laminar and turbulent flames, addresses the problem of flame-wall interaction, and presents a series of theoretical tools used to study the coupling phenomena between combustion and acoustics. The second edition incorporates recent advances in unsteady simulation methods,
Download or read book Combustion written by J. Warnatz and published by Springer Science & Business Media. This book was released on 2006-09-23 with total page 389 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a rigorous treatment of the coupling of chemical reactions and fluid flow. Combustion-specific topics of chemistry and fluid mechanics are considered and tools described for the simulation of combustion processes. This edition is completely restructured. Mathematical Formulae and derivations as well as the space-consuming reaction mechanisms have been replaced from the text to appendix. A new chapter discusses the impact of combustion processes on the atmosphere, the chapter on auto-ignition is extended to combustion in Otto- and Diesel-engines, and the chapters on heterogeneous combustion and on soot formation are heavily revised.
Download or read book Laminar Flame Propagation and Quenching in Natural Gas air Mixtures with Particular Reference to Low Temperatures written by Khare, Jitendra Mai and published by 1978.. This book was released on 1978 with total page 402 pages. Available in PDF, EPUB and Kindle. Book excerpt:
