Download or read book Stability and Liftoff of Non premixed Large Hydrocarbon Flames in MILD Conditions written by Eric M. Walters and published by . This book was released on 2016 with total page 123 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Moderate or Intense Low-oxygen Dilution (MILD) combustion regime has received interest from the industrial furnace and gas turbine engine industries due to attractive properties of reduced NO[subscript x] emissions and high thermal efficiency. MILD combustion is characterized by low oxygen concentrations (i.e. 3%-9% by volume) and high reactant temperatures. A fundamental understanding of the physics governing MILD combustion is required to design effective practical combustion devices. While the physics relevant to MILD combustion of small hydrocarbon fuels such as methane and ethylene have been well-characterized, the behavior of large hydrocarbon fuels, such as Jet-A, have not. This is significant because many practical devices such as internal combustion engines and gas turbine engines are designed to operate using large hydrocarbon fuels. With this background and motivation, the focus of the current study was to understand the mechanisms governing stability and ignition of these flames in the MILD regime. To this end, a series of experimental and numerical studies were conducted to identify the physics governing lifted large hydrocarbon flames in the MILD regime. A jet in hot coflow (JHC) burner was used to stabilize a large hydrocarbon flame in a laboratory environment. The coflow used a premixed CH4/H2 secondary burner to provide an oxidizer stream at high temperature and with low oxygen concentration, which emulates MILD conditions. The coflow temperature was varied between 1300K and 1500K and the oxygen concentration was varied between 3% and 9% by volume. Three different large hydrocarbon fuels (i.e. Jet-A and two experimental fuels) were vaporized and issued into the hot coflow, with Reynolds numbers based on the inner jet diameter ranging from 3,750 to 10,000. The fuel jet exit temperature was varied from 525K to 625K. The liftoff heights of the resulting flames were measured using OH* chemiluminescence, as the flames were not always visible. Opposed flow laminar diffusion flames simulations were employed to determine how the interaction between chemistry and strain may affect flame stability. Ignition delay calculations were used to determine how ignition chemistry may affect flame liftoff without considering the effect of mixing. Several conclusions were made from the measurements and simulations. Oscillation of the instantaneous flame liftoff height was observed and was attributed to the cyclic advection of burned fluid downstream and the subsequent autoignition of unburned fluid. An increase in the fuel jet temperature was found to stabilize the flames closer to the jet exit, which was attributed to an increase in entrainment caused by higher fuel jet velocities. Flames in a coflow with 3% O2 at an exit temperature of 1300K were found to exhibit a decrease in liftoff height with increasing fuel jet Reynolds number. This counter-intuitive trend was not observed in flames burning in a coflow with higher temperatures or in coflows with higher O2 concentrations. The decrease in flame liftoff height with Reynolds number was attributed to the transport of formaldehyde into unburned mixture via the observed oscillations in the flame base. This conclusion was supported by both PLIF measurements performed by previous researchers on gaseous MILD flames and by numerical calculations. Opposed flame simulations indicated that formaldehyde production was increased with strain rate, which is analogous to an increase in the fuel jet velocity. Ignition delay calculations indicated that formaldehyde addition decreased ignition delay times, which results in lower flame liftoff heights. Opposed flow flame simulations indicated that the effect of changes in CH2O production was diminished at increased coflow oxygen levels (i.e. 6% and 9%) and elevated coflow temperatures (i.e. 1400K and 1500K) due to lower formaldehyde production.
Download or read book MILD Combustion Modelling Challenges Experimental Configurations and Diagnostic Tools written by Alessandro Parente and published by Frontiers Media SA. This book was released on 2021-11-26 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Combined Effects of Dilution and Co flow on the Stability of Lifted Non premixed Gaseous Flames written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This research documents experiments and analysis of turbulent, lifted, non-premixed diffusion flames in co-flow and with dilution with implications for the development and operation of biogas-fueled combustors. Fuels used in this study were methane and ethylene. The diluent used was nitrogen. General trends were observed in the liftoff and reattachment behavior as affected by dilution of the fuel stream. Initial liftoff velocity was observed to decrease linearly with dilution, while initial lift height behavior was bimodal. Reattachment conditions were similar in overall behavior to liftoff conditions. Co-flow effects were not included in liftoff and reattachment studies. Combined effects of dilution and co-flow were also studied. Stabilization height compared to radial stabilization was found to be bimodal, with behavior differing in the potential core region compared with the far-field region. Dilution was found to decrease the radial stabilization distance, and co-flow tended to increase the radial stabilization distance. However, both effects were minor. The major results involve heat release effects. For given stabilization heights, stabilization velocity was found to decrease with dilution faster than laminar burning velocity with dilution. Stabilization height was also found to increase rapidly with dilution beyond a certain diluent concentration. Flames were also found to taper inward and become more cylindrical in shape as dilution increases. Implications for several flame stabilization theories are discussed. Future work for confirming the results of this research are also discussed.
Download or read book An Investigation of the Lift Off Stability of a Turbulent Non premixed Flame written by K.J. Syed and published by . This book was released on 1984 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Stability of Hydrocarbon Jet Diffusion Flames Near Lift off written by Gregory Alan Holscher and published by . This book was released on 1995 with total page 304 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Non premixed Conditions in the Flameholding Recirculation Region Behind a Step in Supersonic Flow written by Amit Thakur and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Due to slower diffusion rate, the heavier fuel had higher local mole fraction in the recirculation region compared to lighter fuel for a unit global fuel mole fraction injected in the test section. Hence fuel molecular weight will affect the non-premixed flame stability limits in scramjet engine; the heavier fuel will have better fuel-lean and worse fuel-rich stability limit compared to lighter fuel. This is in addition to the fact that a lighter fuel such as hydrogen has a much wider flame stability limit than a heavier fuel such as propane. The data obtained in the study can help develop a stability parameter for non-premixed flames and validate computational models.
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 Temporal Stability Analysis of Non premixed Circular Jet Flames written by Andrew S. Ulrich and published by . This book was released on 2009 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Global Consumption Speeds of Premixed Large Hydrocarbon Fuel Air Turbulent Bunsen Flames written by Aaron Jesse Fillo and published by . This book was released on 2016 with total page 110 pages. Available in PDF, EPUB and Kindle. Book excerpt: Large-hydrocarbon fuels are used for ground and air transportation because of their high energy-density and will be for the foreseeable future. However, combustion of large-hydrocarbon fuels in a turbulent environment is poorly understood and difficult to predict. The turbulent flame speed, which is the velocity at which a flame front propagates through a turbulent fuel and air mixture, is a key property in turbulent combustion. The turbulent flame speed can be used as a model input parameter for tur- bulent combustion simulations. However, turbulent flame speeds for large-hydrocarbon fuels are largely unknown. These values are needed to improve combustion models and enhance understanding of the physics and chemistry that control turbulent combustion of large-hydrocarbon fuels. The objective of this study is to measure the turbulent flame speed of large-hydrocarbon fuels and to identify key physics in the turbulent combustion of these fuels. This is motivated by the use of the turbulent flame speeds in modeling combustion in practical devices and the significant use of large-hydrocarbons in these devices. This research has broad implications for society and industry; both the Federal Aviation Administration and gas turbine engine companies have called for research on the turbulent flame speeds of large-hydrocarbon fuels. The turbulent flame speed in this work is defined as the global consumption speed, and is measured for three fuels on a turbulent Bunsen burner. The Reynolds number, turbulence intensity, preheat temperature, and equivalent ratio can be independently controlled using the burner. A conventional Jet-A fuel, known as A2, is used as a reference because of its common use in commercial and military aviation. A2 is compared to bi-modal and quadra-modal blends referred to as C1 and C5, respectively. These fuels are selected as they have similar heat releases and laminar flame speeds. Time-averaged line of site images of OH*, CH*, and CO2* chemiluminescence are used to determine an the average flame front area. This flame area is used to determine the global consumption speed. The global consumption speed is measured for Reynolds number and equivalence ratio ranging between 5.000-10.000 and 0.7-1, respectively. Turbulence intensities are varied between 10% and 20% of the bulk flow velocity. The global consumption speed increases with turbulence intensity and Reynolds number for all fuels. Global consumption speeds for A2 and C5 match within 5% at all conditions. Conversely, the global consumption speed of C1 is up to 22% lower than A2 or C5. These results indicate the global consumption speed is sensitive to turbulent velocity fluctuations, bulk flow velocity, and fuel chemistry. These results together suggest the global consumption speed is additionally sensitive to flame stretch. Dimensional analysis is used to isolate and identify sensitivities of the global consumption speed to turbulent velocity fluctuations, bulk flow velocity, global stretch rate, and fuel chemistry. A clear sensitivity to fuel chemistry is observed and is affected by aromatic and alkane content. A2 and C5 have higher global consumptions speeds and increased stability; these fuels have shorter average hydrocarbon chain lengths and higher aro- matic content than C1. In addition, the global consumption speed is highly sensitive to turbulence intensity of the flow; the turbulent flame speed increases an average of 30% for all fuels between the minimum and maximum turbulence intensity cases. Results are attributed to a strong sensitivity of the global consumption speed to flame stretch and a strong coupling of turbulence and fuel chemistry effects. These conclusions agree with the available literature and provide a foundational understanding of the sensitivities of the global consumption speed for large-hydrocarbon fuels.
Download or read book Electric Field Induced Stability Modifications in Pre mixed Hydrocarbon Flames written by and published by . This book was released on 2006 with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work focuses upon the effects of electric fields on the stability of pre-mixed hydrocarbon flames fueled by methane, propane and butane. For all fuels studied, over varying flow rates and equivalence ratios, electric-field-induced modification of the flame front stability over wide ranges has been observed and documented. Specifically, the electric pressure effect has been used to force pre-mixed hydrocarbon/air flame fronts to transition from flow-induced hydrodynamic-instability-dominated behavior, to field-stabilized laminar flow, and finally to field-induced thermal-diffusive-instability-dominated turbulent flame fronts. The effects are best described from a combustion dynamics viewpoint as a continuously variable electric-field-induced diminution of the flame Lewis number from typical values (> 1), past the flame critical Lewis number (0.6-0.9), to thermal-diffusive-instability dominated values below the critical Lewis number at higher applied potentials. A possible field-driven ion chemistry process that could produce those effects is the dissociative recombination of the flame ion (H30+) at the burner surface.
Download or read book Combined Effects of Dilution and Co flow on the Stability of Lifted Non premixed Gaseous Flames written by David Andrew Wilson and published by . This book was released on 2005 with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt: Keywords: dilution, co-flow, non-premixed flame, diffusion flame, combustion, flame stability.
Download or read book An Experimental Study of Flame Stabilization Mechanisms in Turbulent Non premixed Jet Flames Under Autoignitive Conditions written by Aravind Ramachandran and published by . This book was released on 2019 with total page 137 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Combustion Instabilities in Non premixed Opposed flow Tubular Flames written by Scott William Shopoff and published by . This book was released on 2010 with total page 85 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book High Temperature Air Combustion written by Hiroshi Tsuji and published by CRC Press. This book was released on 2002-12-03 with total page 425 pages. Available in PDF, EPUB and Kindle. Book excerpt: Maximize efficiency and minimize pollution: the breakthrough technology of high temperature air combustion (HiTAC) holds the potential to overcome the limitations of conventional combustion and allow engineers to finally meet this long-standing imperative. Research has shown that HiTAC technology can provide simultaneous reduction of CO2 and nitric
Download or read book Design and Performance of Gas Turbine Power Plants written by William R. Hawthorne and published by Princeton University Press. This book was released on 2015-12-08 with total page 582 pages. Available in PDF, EPUB and Kindle. Book excerpt: Volume XI of the High Speed Aerodynamics and Jet Propulsion series. Edited by W.R. Hawthorne and W.T. Olson. This is a comprehensive presentation of basic problems involved in the design of aircraft gas turbines, including sections covering requirements and processes, experimental techniques, fuel injection, flame stabilization, mixing processes, fuels, combustion chamber development, materials for gas turbine applications, turbine blade vibration, and performance. Originally published in 1960. The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These editions preserve the original texts of these important books while presenting them in durable paperback and hardcover editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.
Download or read book Gas Turbine Emissions written by Timothy C. Lieuwen and published by Cambridge University Press. This book was released on 2013-07-08 with total page 385 pages. Available in PDF, EPUB and Kindle. Book excerpt: The development of clean, sustainable energy systems is a preeminent issue in our time. Gas turbines will continue to be important combustion-based energy conversion devices for many decades to come, used for aircraft propulsion, ground-based power generation, and mechanical-drive applications. This book compiles the key scientific and technological knowledge associated with gas turbine emissions into a single authoritative source.
Download or read book Fundamentals of Combustion Processes written by Sara McAllister and published by Springer Science & Business Media. This book was released on 2011-05-10 with total page 315 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fundamentals of Combustion Processes is designed as a textbook for an upper-division undergraduate and graduate level combustion course in mechanical engineering. The authors focus on the fundamental theory of combustion and provide a simplified discussion of basic combustion parameters and processes such as thermodynamics, chemical kinetics, ignition, diffusion and pre-mixed flames. The text includes exploration of applications, example exercises, suggested homework problems and videos of laboratory demonstrations
