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 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 Stabilization Zone Structure in Jet Diffusion Flames from Liftoff to Blowout written by T.H. Chen and published by . This book was released on 1989 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Stability of Free Jet Diffusion Flames written by Rudolf Günther and published by . This book was released on 1979 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Burner Stabilities of Jet Diffusion Flames written by James Phillip Seaba and published by . This book was released on 1990 with total page 266 pages. Available in PDF, EPUB and Kindle. Book excerpt: The near field lift-off phenomena associated with jet diffusion flames were investigated. Lift-off is defined as the instant when the luminous flame zone detaches from the burner exit, stabilizing itself downstream. The lift-off of the jet diffusion flames were studied using a fuel jet centered in a large coflowing air annulus. Fuels used consisted of methane and propane. The fuels are diluted with nitrogen, argon, and helium. Annulus, diluted fuel, and external nozzle geometry effects are studied for the jet diffusion flame. The jet diffusion flame is sensitive to the annulus velocity, the lift-off velocity decreasing with increasing annular velocity. Lift-off velocity decreases as dilution concentrations of the fuel jet increase. The external geometry effects influence the lift-off velocity, especially at higher annular flow rates. Two theories have explained the lift-off of jet diffusion flames. The locally premixed theory which assumes that the fuel and oxidant are fully premixed prior to combustion. The lift-off of the flame zone occurs due to the convective velocity of the premixed reactants exceeding the local flame speed. The second theory, the laminar flamelet model, states that the diffusion of reactants into the flame zone exceeds the chemical reaction rate, causing the flame to extinguish at the flame base, lifting the flame from the nozzle to a position downstream. The two models were evaluated by the different lift-off velocities produced by annulus and diluent effects. Laser Doppler anemometry (LDA) was used to characterize the flow field at and near the base of the jet diffusion flame. The local straining rate across the flame was approximated by the gradient of the mean radial velocity in the radial direction for the pure and diluted methane conditions. The straining rate was in qualitative agreement with that reported in the literature for counter-flow methane diffusion flames near extinction.
Download or read book Simulation and Stability Analysis of Jet Diffusion Flames written by Joseph W. Nichols and published by . This book was released on 2005 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Stability of Free jet Diffusion Flames written by Amarnath V. Kapur and published by . This book was released on 1969 with total page 126 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book External Geometry Effects on the Lift off Process of Jet Diffusion Flames written by Vincent F. B. Liu and published by . This book was released on 1992 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Joint Meeting of the U S Sections of the Combustion Institute Western States Central States Eastern States written by and published by . This book was released on 2005 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental and CFD Investigations of Lifted Tribrachial Flames written by Zhiliang Li and published by . This book was released on 2010 with total page 193 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experimental measurements of the lift-off velocity and lift-off height, and numerical simulations were conducted on the liftoff and stabilization phenomena of laminar jet diffusion flames of inert-diluted C3H and CH4 fuels. Both non-reacting and reacting jets were investigated, including effects of multi-component diffusivities and heat release (buoyancy and gas expansion). The role of Schmidt number for non-reacting jets was investigated, with no conclusive Schmidt number criterion for liftoff previously known in similarity solutions. The cold-flow simulation for He-diluted CH4 fuel does not predict flame liftoff; however, adding heat release reaction leads to the prediction of liftoff, which is consistent with experimental observations. Including reaction was also found to improve liftoff height prediction for C3H flames, with the flame base location differing from that in the similarity solution--the intersection of the stoichiometric and iso-velocity contours is not necessary for flame stabilization (and thus lift-off). Possible mechanisms other than that proposed for similarity solution may better help to explain the stabilization and liftoff phenomena. The stretch rate at a wide range of isotherms near the base of the lifted tribrachial flame were also quantitatively plotted and analyzed.
Download or read book Thermo Gas Dynamics of Hydrogen Combustion and Explosion written by Boris E. Gelfand and published by Springer Science & Business Media. This book was released on 2012-02-13 with total page 339 pages. Available in PDF, EPUB and Kindle. Book excerpt: The potential of hydrogen as an important future energy source has generated fresh interest in the study of hydrogenous gas mixtures. Indeed, both its high caloricity and reactivity are unique properties, the latter underscoring safety considerations when handling such mixtures. The present monograph is devoted to the various aspects of hydrogen combustion and explosion processes. In addition to theoretical and phenomenological considerations, this work also collates the results of many experiments from less well known sources. The text reviews the literature in this respect, thereby providing valuable information about the thermo-gas-dynamical parameters of combustion processes for selected experimental settings in a range of scientific and industrial applications.
Download or read book Jet Fire Due to Gas Leakage written by Kuibin Zhou and published by Springer Nature. This book was released on with total page 137 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental Studies on the Leading Edge and Local Extinction in Lifted Jet Diffusion Flames written by and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Several researchers have examined the concept of flame stability and there has been little agreement regarding the reasons governing this phenomenon. The experiments described within were devised to establish the dominating stabilization mechanism in lifted flames. Specifically, the flame base of lifted methane-jet diffusion flames were examined through the use of various combinations of synchronized laser-based techniques involving particle image velocimetry (PIV), planar laser-induced fluorescence (PLIF), and Rayleigh scattering. Results indicate the presence of a structure termed a flame. Results involving the gradient in the Rayleigh signal across the flame base, in addition to two-shot CH-PLIF interpretations support the leading-edge flame as a primary stabilization mechanism. The extent of premixing upstream of the flame base has been a major source of disagreement in the past. The simultaneous Rayleigh and CH-PLIF images indicate the base of the lifted flame lies in a region that is within the flammability limits of methane burning in air. Furthermore, the average velocity at the stabilization point is 1.18 m/s (as determined from the simultaneous CH-PLIF and PIV investigation); this value is comparable to three times the laminar burning velocity of methane (~ 3S), thereby supporting previous numerical triple flame simulations. Results from the joint two-shot CH-PLIF and PIV technique show that the flame base velocity is independent of the flow conditions when the flame is stationary during the time separation of the CH-PLIF pulses. Specifically, flames with Re flow conditions. Finally, regions of local extinction -- as indicated by openings in the CH profiles -- were examined. Results from four experiments (simultaneous CH-PLIF and PIV, simultaneous CH-PLIF and OH-PLIF, simultaneous CH-PLIF and Rayleigh scattering, and simultaneous two-shot CH-PLIF and PIV) provide complementary information regarding the role of large-scale fuel vortices in initiat.
Download or read book Simulation of Flame Stabilization of Lifted Turbulent Jet Diffusion Flames written by Ming Chen and published by . This book was released on 2000 with total page 179 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Publications of the National Institute of Standards and Technology Catalog written by National Institute of Standards and Technology (U.S.) and published by . This book was released on 1991 with total page 480 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Stability Limits of Hydrogen air Coflow Jet Diffusion Flames written by F. Takahashi and published by . This book was released on 1990 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
