Download or read book An Experimental Study of Ignition Effects and Flame Growth Over a Thin Solid Fuel in Low Speed Concurrent Flow Using Drop Tower Facilities written by Richard Dale Pettegrew and published by . This book was released on 1996 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Experimental Study of Ignition Effects and Flame Growth Over a Thin Solid Fuel in Low Speed Concurrent Flow Using Drop Tower Facilities written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-17 with total page 136 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental study of ignition and flame growth over a thin solid fuel in oxidizer flow speeds from 0 to 10 cm/sec concurrent flow was performed. This study examined the differences between ignition using a resistively heated wire (woven in a sawtooth pattern over the leading edge of the fuel), and a straight resistively heated wire augmented by a chemical ignitor doped onto the leading edge of the fuel. Results showed that the chemical system yielded non-uniform ignition bursts, while the system using only the hotwire gave more uniform ignition. At speeds up to 2.5 cm/sec, the chemical system yielded non-uniform pyrolysis fronts, while the hotwire system gave more uniform pyrolysis fronts. At speeds of 5 cm/sec or greater, both systems gave uniform pyrolysis fronts. The chemically-ignited flames tended to become too dim to see faster than the hotwire-ignited flames, and the flame lengths were observed to be shorter (after the initial burst subsided) for the chemical system for all speeds. Flame and pyrolysis element velocities were measured. Temperature profiles for selected tests were measured using thermocouples at the fuel surface and in the gas phase. Comparisons between the flame element velocities and peak temperatures recorded in these tests with calculated spread rates and peak temperatures from a steady-state model are presented. Agreement was found to be within 20% for most flame elements for nominal velocities of 5 cm/sec and 7.5 cm/sec. Pettegrew, Richard Dale Glenn Research Center IGNITION; DIFFUSION FLAMES; PYROLYSIS; TEMPERATURE PROFILES; COMBUSTION; DROP TOWERS; VAPOR PHASES; TEMPERATURE MEASUREMENT; THERMOCOUPLES; IMAGE ANALYSIS; ERROR ANALYSIS; FLOW VELOCITY; STEADY STATE; IMAGING TECHNIQUES; OXIDIZERS; ELECTRIC WIRE; NONUNIFORMITY; SURFACE PROPERTIES; FUELS...

Download or read book Fourth International Microgravity Combustion Workshop written by and published by . This book was released on 1997 with total page 546 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Microgravity Combustion written by Howard D. Ross and published by Elsevier. This book was released on 2001-09-03 with total page 601 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides an introduction to understanding combustion, the burning of a substance that produces heat and often light, in microgravity environments-i.e., environments with very low gravity such as outer space. Readers are presented with a compilation of worldwide findings from fifteen years of research and experimental tests in various low-gravity environments, including drop towers, aircraft, and space.Microgravity Combustion is unique in that no other book reviews low- gravity combustion research in such a comprehensive manner. It provides an excellent introduction for those researching in the fields of combustion, aerospace, and fluid and thermal sciences. * An introduction to the progress made in understanding combustion in a microgravity environment* Experimental, theoretical and computational findings of current combustion research* Tutorial concepts, such as scaling analysis* Worldwide microgravity research findings

Download or read book An Experimental Study of Low speed Concurrent flow Flame Spread Over a Thin Fuel written by Gary David Grayson and published by . This book was released on 1991 with total page 166 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book 41st AIAA Aerospace Sciences Meeting Exhibit written by and published by . This book was released on 2003 with total page 594 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Concurrent Flow Flame Spread Study written by Hai-Tien Loh and published by . This book was released on 1992 with total page 147 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental study has been performed of the spread of flames over the surface of thick PMMA and thin filter paper sheets in a forced gaseous flow of varied oxygen concentration moving in the direction of flame spread. It is found that the rate of spread of the PMMA pyrolysis front is time independent, linearly dependent on the gas flow velocity and approximately square power dependent on the oxygen concentration of the gas . The experimental data with thin filter paper sheets shows that the flame spread rate is independent of the flow velocity for forced flow conditions and linearly dependent on the oxygen concentration of the flow. In both experiments, it was found that the flame spread rate data can be correlated in terms of parameter deduced from heat transfer considerations only. This indicates that heat transfer from the flame to the condensed fuel is the primary mechanism controlling the spread of flame. Finite rate chemical kinetic effects have apparently a small influence on the flame spread process itself. Analytical and numerical methods were also employed to study theoretically the name spread process over thermally thick fuel and the influence on the flow field behavior in the presence of a flame. It is found that an analytical model based on a quasi-steady analysis and the flame sheet approximation predicts a square power law dependence of the flame spread rate on the flow oxygen concentration and a linear dependence on the flow velocity. The correct and encouraging qualitative descriptions of the flow structure and surface fluxes in the region downstream from the pyrolysis front.

Download or read book The Combined Effect of Oxidizer Flow Velocity Turbulence and Oxygen Concentration on Ignition and Concurrent Flame Spread on Solid Fuels written by Yu Hang Christopher Chao and published by . This book was released on 1994 with total page 500 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Solid Fuel Flame Spread and Mass Burning in Turbulent Flow written by Liming Zhou and published by . This book was released on 1991 with total page 480 pages. Available in PDF, EPUB and Kindle. Book excerpt: The flow turbulence also has a significant effect on the flame extinction conditions, resulting in a smaller extinction velocity for larger flow turbulence intensity. For concurrent flow flame spread, it is found that the flow turbulence decreases the flame spread rate for both floor and ceiling geometries, mainly as a result of the flame length shortening at high turbulence intensity. It is also found that flow velocity intensifies the spread of the flame. The experimental data of flame spread rate, flame length and surface heat flux agree well with the formula obtained from a simplified thermal model, indicating that the heat transfer from flame to solid surface is the dominant controlling mechanism in the turbulent concurrent flame spread and, that the gas phase chemical reaction is of secondary importance.

Download or read book Solid Fuel Combustion in a Forced Turbulent Flat Plate Flow written by Liming Zhou and published by . This book was released on 199? with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental study is conducted of the effect of flow velocity, grid-generated turbulence and buoyancy on the combustion of a solid fuel in a flat plate boundary layer flow. The effect of buoyancy is determined by comparing the surface regression rates, flame characteristics, and exhaust products composition for the solid burning in a flow and ceiling orientation. Measurements are presented for the ceiling surface regression rate of PMMA sheets burning in air, and compared with previously obtained floor data. It is concluded that buoyancy has two major, and counteracting, effects. One is to affect the heat transfer by shifting the flame away from the surface in the floor burning and closer to the surface in the ceiling. The other is also due to the flame shifting and the instabilities associated with it that favors, in the floor case, the mixing of the reactants, and consequently the overall heat release rate. In the ceiling, the proximity of the flame to the cold surface causes quenching of the reaction, and the stability of the flame hampers reactants mixing, both of which reduce the heat generation rate. The overall result of these two counteracting mechanisms is that the surface regression rates are not that different in both geometries, although the composition of the combustion products are quite different.

Download or read book A Gallery of Combustion and Fire written by Charles E. Baukal, Jr. and published by Cambridge University Press. This book was released on 2020-09-03 with total page 193 pages. Available in PDF, EPUB and Kindle. Book excerpt: A Gallery of Combustion and Fire is the first book to provide a graphical perspective of the extremely visual phenomenon of combustion in full color. It is designed primarily to be used in parallel with, and supplement existing combustion textbooks that are usually in black and white, making it a challenge to visualize such a graphic phenomenon. Each image includes a description of how it was generated, which is detailed enough for the expert but simple enough for the novice. Processes range from small scale academic flames up to full scale industrial flames under a wide range of conditions such as low and normal gravity, atmospheric to high pressures, actual and simulated flames, and controlled and uncontrolled flames. Containing over 500 color images, with over 230 contributors from over 75 organizations, this volume is a valuable asset for experts and novices alike.

Download or read book Ignition and Flame Growth in Concurrent Forced Flow Over Thick Solids written by Ya-Ting Tseng and published by . This book was released on 2007 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Opposed Flow Flame Spread Over Solid Fuels in Different Burning Regimes written by Luca Carmignani and published by . This book was released on 2019 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: Several aspects of opposed-flow flame spread are experimentally investigated because of their relevance in fire safety studies. Different burning regimes based on the intensity of the opposed flow velocity are identified for acrylic fuels. In downward flame spread, where the flow around a flame is only naturally induced by gravity, the spread rate is highly dependent on fuel size and geometry. The fuel cross-sectional shape is experimentally varied, and a formula which takes into account geometrical effects is proposed by extending previous solutions for two-dimensional flames. The burning region of a solid fuel shows a consistent slope due to the competition between flame spread and surface regression. The angle at the vertex of the pyrolysis region, called burn angle, can be used to indirectly calculate the fuel burning rate. The burn angle depends on fuel thickness; a numerical model and a scale analysis are used to explore the reasons for this behavior. Next, the effect of a forced flow is investigated. The extreme case of blow-off extinction over thin fuels is considered, with flames extinguishing at locations determined by the flow velocity. Results suggest that the interaction between fuel and flow field is more important than the dependence on fuel thickness. The evolution of flame structure and pyrolysis also appear to be driven by flow interactions. A scale analysis is used to explore these dependencies. Finally, previous microgravity experiments are used to explore differences and similarities with ground-based results. By suppressing the buoyant flow, flame radiation becomes essential for the flame spread process. The experimental conditions are simulated numerically to describe the importance of a developing boundary layer in this regime. A numerical parametric study of the radiative emission of flames in microgravity, inspired by the experimental data, shows its dependence on flame area, mass burning rate and flame temperature by changing the burning conditions. For these small flames, soot does not seem to dominate flame radiation, although its generation increases with fuel thickness, oxygen concentration and flow velocity. The experiments in microgravity considered in this work showed flame extinction in a quiescent environment. However, two acrylic cylinders at higher oxygen concentrations from a previous investigation can burn vigorously. To clarify whether these flames are stable, a scale analysis is used to study the influence of surface curvature on radiation losses.

Download or read book Investigation of Opposed Flow Flame Spread Over Solid Fuels written by Sarzina Hossain and published by . This book was released on 2021 with total page 203 pages. Available in PDF, EPUB and Kindle. Book excerpt: The opposed flow flame spread over flat solid fuels is of fundamental importance to the field of fire safety. Several features of opposed flow flame spread are experimentally, numerically and analytically investigated.Thermally thick slab of PolyMethylMethAcrylate (PMMA) was used to study the effects of opposed flow velocity (8-58 cm/s) and fuel thickness (6.6, 12.1 and 24.5 mm). The experiments were conducted with a Narrow Channel Apparatus (NCA) at Michigan State University (MSU). The flame spread rate results show that the maximum flame spread occurs at a lower flow velocity for relatively thicker fuel. The peak flame spread rate for 6.6 mm, 12.1 mm and 24.5 mm occurs at 18.5 cm/s, 12.1 cm/s and 10.3 cm/s, respectively. Several flame spread regimes: thermal, chemical and regressive burning are identified from the results. Flame spread regimes are usually depend on the opposed flow velocity. However, the flame spread rate for newly found regressive burning regime is independent of flow velocities. Visual observation of the flame indicates that the flame intensity augments with flow velocity for all thicknesses of PMMA. The comparison between NCA data and legacy data for similar material (PMMA) and thickness (12.1 mm) demonstrated excellent agreement, subject to the extension of the numerical and theoretical analysis to include relevant features of the flame spread stretch rate theory. The results also demonstrated the effectiveness of the stretch rate theory for markedly different experimental configurations. Although thick slab is used to perform tests, complete burn out of the samples for thickness 6.6 and 12.1 mm are observed at high opposed flow velocities (30 ℗ł 5 cm/s and higher). On contrary, the thickest sample (24.5 mm) did not go through complete burning. This indicates the nature of surface regression and its impact on flame spread rate.Based on the results, it can be emphasized that the factors controlling the flame front advancement involves both flame spread and surface regression. So, the burnt samples at different opposed flow velocities of 24.5 mm thickness from flame spread study is measured for surface regression depth experimentally. A semi-empirical correlation is developed to relate the flame spread and regression and to determine the mass loss rate from the burnt fuel surface. Mass loss rate is also a key aspect of characterizing the flammability of materials. Results show that the power law dependency of mass loss rate changes with opposed flow velocity. A comparison of power law exponents of current results and results from literature are made. Results demonstrate that the power law dependency at flow velocity 8.2, 10.3 and 12 cm/s is -0.5 which show excellent agreement with legacy work.Next, another study is conducted on the post-flame-spread 24.5 mm PMMA sample, burnt at opposed flow velocity 15 cm/s. Visual observation of post-burn sample shows the formation of significant number of internal bubbles. Three samples of similar thickness burnt at similar condition were investigated for bubble count and size. Results indicate higher and smaller bubble presence near the leading edge of the flame compared to the trailing edge side. Comparison of bubble size distribution with several distribution function demonstrates that the bubble size shows good agreement with Log-normal distribution function.Finally, the transient regression rate has been investigated analytically and numerically. The effect of external heat flux simulating flame heat flux is analyzed for PMMA considering it as an ideal-vaporizing solid. Results indicate a strong dependency of heat flux on material regression for a time duration. After a certain time period, the regression rate became insensitive to heat flux change. A scale analysis is performed to compare the analytical-numerical regression rate results with experimental surface regression depth. The predicted regression followed a similar pattern as the experimental surface regression.

Download or read book An Experimental Study of Opposed Flow Diffusion Flame Extinction Over a Thin Fuel in Microgravity written by Paul Vincent Ferkul and published by . This book was released on 1988 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effect of Oxygen Concentration on Flame Spread Over Thin Fuels in Different Regimes written by and published by . This book was released on 2018 with total page 70 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this research is to investigate how oxygen concentration, opposed flow velocity and thickness of a thin PMMA fuel affect the flame spread rate and flame extinction in microgravity. The flame spread rate increases with an increase in oxygen concentration. The critical oxygen level, which is the minimum concentration for a flame to spread, is inversely related to the fuel thickness. For fuel thickness above and below a critical thickness, the flame spread rate increases and decreases with a decrease in fuel thickness, respectively. Also, an unexpected extinction is discovered. The critical fuel thickness is inversely related to the opposed flow velocity. The flame spread rate decreases when the opposed flow velocity decreases. Unexpected extinction is discovered when oxygen level is low and opposed flow is absent or weak. The simulation results are consistent with the available experimental results obtained by NASA. For a quiescent environment in microgravity, the critical oxygen level increases with the fuel thickness while the critical oxygen level decreases with the fuel thickness for environments with an opposed flow. The research on how a flame extinguishes reveals that the flame temperature in the anomaly region is lower than the flame temperature in the normal region. A flame extinguishes when the percentage surface radiation loss, which is the ratio of the surface radiation loss to heat generated from combustion, is higher than 45% with an opposed flow and 48% in quiescent environment.

Download or read book Ignition and Flame Growth in Lean Gas air Mixtures written by Tor Øyvind Ask and published by . This book was released on 1992 with total page 230 pages. Available in PDF, EPUB and Kindle. Book excerpt: