Download or read book Flame Spread and Extinction Over Solids in Buoyant and Forced Concurrent Flows Model Computations and Comparison with Experiments written by Sheng-Yen Hsu and published by . This book was released on 2009 with total page 250 pages. Available in PDF, EPUB and Kindle. Book excerpt: A detailed three-dimensional model for steady flame spread over thin solids in concurrent flows is used to compare with existing experiments in both buoyant and forced flows. This work includes (1) several improvements in the quantitatively predictive capability of the model, (2) a sensitivity study of flame spread rate on input parameters, (3) introduction of flame radiation into the buoyant-flow computations and (4) quantitative comparisons with two sets of buoyant upward spread experiments using cellulosic samples and a comparison with forced downwind spread tests using wider cellulosic samples. In additional to sample width and thickness, the model computation and experimental comparison cover a substantial range of environmental parameters such as oxygen percentage, pressure, velocity and gravity that are of interest to the applications to space exploration. In the buoyant-flow comparison, the computed upward spread rates quite favorably agree with the experimental data. The computed extinction limits are somewhat wider than the experimental limits based on only one set of older test data (the only one available). Comparison of the flame thermal structure (also with this set of older data) shows that the computed flame is longer and there is structure difference in the flame base zone. This is attributed to the sample cracking phenomenon near the fuel burnout, a mechanism not treated in the model. Comparison in forced concurrent flows shows that the predicted spread rates are lower than the experimental ones if the flames are short but higher than the experimental ones if the flames are long. It is believed that the experimental flames may have not fully reached the steady states at the end of 5-second drop. The effect of gas-phase kinetic rate on concurrent flame spread rates is investigated through the variation of the pre-exponential factor. It is found that flames in forced flow are less sensitive to the change of kinetics than flames in buoyant flow; and narrow samples are more sensitive to the change of kinetics compared with wide samples. The rate of chemical kinetics affects the flame spread rates primarily through two mechanisms: the amount of un-burnt fuel vapors escaping the reaction zone and the induced velocity variation through flame temperature change in the case of the buoyant flames.

Download or read book Material Flammability and Burning Behavior of Thin Solids in Concurrent Forced Flow in Microgravity written by Chengyao Li and published by . This book was released on 2020 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt: Material flammability and burning behaviors of thin solids in concurrent flows in normal and microgravity are studied using a previously-developed transient numerical model. The model consists of an unsteady gas phase and an unsteady solid phase. The gas phase solves full Navier-Stokes equations including mass, momentum, energy and species equations, using Direct Numerical Simulation. A one-step, second-order overall Arrhenius reaction is adopted. Gas phase radiation is considered by solving the radiation transfer equation with a discrete ordinates SN approximation. In the solid phase, conservation equations of the energy and mass are solved. A cotton-fiberglass-blend fabric is considered as the solid material in this research. Test-based two-step decomposition reactions are implemented for the solid pyrolysis. In this work, the following efforts are made: (1) enhancement to the Adaptive Mesh Refinement (AMR) scheme and (2) development of a two-dimensional version of the program (based on the original three-dimensional program). The first effort allows the program to simulate and resolve multiple flames spreading along the surface of the solid combustible. The second effort dramatically reduces the computational cost when simulating flame spread over wide samples. The model is applied to simulate three scenarios: (1) upward flame spread in normal gravity, (2) purely-forced concurrent flow flame spread over a large and wide sample (41 cm wide 94 cm long), and (3) purely-forced concurrent flow flame spread over a moderate size (5 cm wide, 30 cm long) sample. In the first scenario, upward flame spread in normal gravity, the simulations follow the dimension/configuration of a standard test, NASA-STD-6001 Test #1. This test is the current ground-based screening test for materials that are intended for use in space exploration. The tested sample is 5 cm wide and 30 cm long. In the simulation, ambient pressure is the main parameter. At low pressures, the conventional upward flame spread process is observed. As the pressure increases, a special flame splitting phenomenon is observed. The splitting process is presented in details using the solid and gas profiles. It is concluded that the two-step solid pyrolysis is the cause of this special phenomenon. For the second and third scenarios, simulations are performed to support an on-going NASA project Saffire, which consists of a series of large-scale microgravity burning experiments. Concurrent flow speeds at 20 and 25 cm/s are simulated for both large and moderate sized samples. The results of both Saffire experiments and the simulations are presented and compared in detail. The numerical results are also used to interpret the phenomena observed in the experiments. For the wide sample (scenario 2), a parametric study on the sample width (5-41 cm) is conducted, and additional simulations (using the two-dimensional version of the program) at various flow conditions (different flow speeds, ambient pressures, and oxygen percentages) are performed. Based on the simulation results, analytical analysis is conducted and formulations are proposed for flame spread rate and flame length. The proposed formulation for flame spread rate is evaluated using literature data of microgravity experiments and shows seasonable performance.

Download or read book A Model of Concurrent Flow Flame Spread Over a Thin Solid Fuel 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 158 pages. Available in PDF, EPUB and Kindle. Book excerpt: A numerical model is developed to examine laminar flame spread and extinction over a thin solid fuel in lowspeed concurrent flows. The model provides a more precise fluid-mechanical description of the flame by incorporating an elliptic treatment of the upstream flame stabilization zone near the fuel burnout point. Parabolic equations are used to treat the downstream flame, which has a higher flow Reynolds number. The parabolic and elliptic regions are coupled smoothly by an appropriate matching of boundary conditions. The solid phase consists of an energy equation with surface radiative loss and a surface pyrolysis relation. Steady spread with constant flame and pyrolysis lengths is found possible for thin fuels and this facilitates the adoption of a moving coordinate system attached to the flame with the flame spread rate being an eigen value. Calculations are performed in purely forced flow in a range of velocities which are lower than those induced in a normal gravity buoyant environment. Both quenching and blowoff extinction are observed. The results show that as flow velocity or oxygen percentage is reduced, the flame spread rate, the pyrolysis length, and the flame length all decrease, as expected. The flame standoff distance from the solid and the reaction zone thickness, however, first increase with decreasing flow velocity, but eventually decrease very near the quenching extinction limit. The short, diffuse flames observed at low flow velocities and oxygen levels are consistent with available experimental data. The maximum flame temperature decreases slowly at first as flow velocity is reduced, then falls more steeply close to the quenching extinction limit. Low velocity quenching occurs as a result of heat loss. At low velocities, surface radiative loss becomes a significant fraction of the total combustion heat release. In addition, the shorter flame length causes an increase in the fraction of conduction downstream compared to conduction to the fuel. The...

Download or read book NASA Technical Memorandum written by and published by . This book was released on 1994 with total page 492 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 A Model of Concurrent Flow Flame Spread Over a Thin Solid Fuel written by Paul Vincent Ferkul and published by . This book was released on 1993 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Numerical Modeling of Flame Spread Over Spherical Solid Fuel Under Low Speed Flow in Microgravity written by Makoto Endo and published by . This book was released on 2015 with total page 233 pages. Available in PDF, EPUB and Kindle. Book excerpt: Flame spread over solid fuel presents distinctive characteristics in reduced gravity, especially when the forced flow velocity is low. The lack of buoyancy allows a blue, dim flame to sustain where the induced velocity would otherwise blow it off. At such low velocities, a quenching limit exists where the soot content is low and the effect of radiative heat loss becomes important. The objective of this study is to establish a high fidelity numerical model to simulate the growth and extinction of flame on solid fuels in a reduced gravity environment. The great importance of the spectral dependency of the gas phase absorption and emission were discovered through the model development and therefore, Statistical Narrow-Band Correlated-k (SNB-CK) spectral model was implemented.The model is applied to an experimental configuration from the recent space experiment, Burning And Suppression of Solids (BASS) project conducted aboard the International Space Station. A poly(methyl methacrylate) (PMMA) sphere (initial diameter of 2cm) was placed in a small wind tunnel (7.6cm x 7.6cm x 17cm) within the Microgravity Science Glovebox where flow speed and oxygen concentration were varied.Data analysis of the BASS experiment is also an important aspect of this research, especially because this is the first space experiment that used thermally thick spherical samples. In addition to the parameters influencing the flammability of thin solids, the degree of interior heat-up becomes an important parameter for thick solids. For spherical samples, not only is the degree of internal heating constantly changing, but also the existence of stagnation point, shoulder, and wake regions resulting in a different local flow pattern, hence a different flame-solid interaction.Parametric studies using the numerical model were performed against (1) chemical reaction parameters, (2) forced flow velocity, (3) oxygen concentration and (4) amount of preheating (bulk temperature of the solid fuel). Flame Spread Rate (FSR) was used to evaluate the transient effect and maximum flame temperature, standoff distance and radiative loss ratio were used to evaluate the spontaneous response of the gas phase to understand the overall response of the burning solid fuel. After evaluating the individual effect of each parameter, the efficacy of each parameter was compared. Selected results of this research are:[1]Experimental data from BASS and numerical simulation both showed that within the time periodbetween ignition until the flame tip reaches the shoulder of the sample, the flame length and timehave almost a linear relation.[2]Decreasing forced flow velocity increases the radiative loss ratio whereas decreasing oxygen molefraction decreases the radiative loss ratio. This finding must be considered in the effort to replicatethe behavior of flame spread over thick solid fuels in microgravity on earth.[3]Although the standoff distance will increase when the forced flow velocity is decreased as well aswhen the oxygen mole fraction is decreased, the forced flow velocity has a much stronger effect onthe standoff distance than the oxygen mole fraction.[4]Unlike the previous two comparisons, the effect of forced flow velocity and oxygen mole fraction onthe maximum flame temperature was at similar level, reduction of either parameter would result inlowering the maximum flame temperature.[5]The effect of preheating on the flame spread rate becomes stronger when either the oxygen flowrate or forced flow velocity becomes larger. Depending on which element is more important, we candistinguish oxygen flow rate driven flame spread from preheating driven flame spread.Findings of this research are being utilized in the design of the upcoming space experiment, Growth and Extinction Limits of solid fuel (GEL) project. This research is supported by the National Aeronautics and Space Administration (NASA). This work made use of the High Performance Computing Resource in the Core Facility for Advanced Research Computing at Case Western Reserve University and the Ohio Supercomputer Center.

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 Fifth International Microgravity Combustion Workshop written by and published by . This book was released on 1999 with total page 552 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 Numerical Computation of Low speed Concurrent Flow Flame Spread in Mixed Buoyant and Forced Flow written by Paul V. Ferkul and published by . This book was released on 1993 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Chemical and Physical Processes in Combustion written by Combustion Institute (U.S.). Eastern States Section. Fall Technical Meeting and published by . This book was released on 1993 with total page 594 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Forced Opposed Flow Flame Spread Over Flat Solid Fuels in the Thermal Near Quiescent and Chemical Kinetic Regimes written by Jeffrey S. West and published by . This book was released on 1998 with total page 842 pages. Available in PDF, EPUB and Kindle. Book excerpt: A detailed numerical model of opposed-flow flame spread over solid fuels is developed. The model is used to study flame spread in three regimes of flame spread; the Thermal, Chemical Kinetic and Near Quiescent Regimes. Simplifying assumptions that have been historically applied to this problem are investigated and their effect on the flame spread rate and flame structure are quantified in each regime. A semi-empirical flame spread formula for thermally thick fuels is developed from knowledge of the dominant simplifying assumptions in this regime. Spread rate predictions compare well to experimental and computed results. This semi-empirical model provides field variables which previous theories are unable to predict. Mechanisms of heat transfer ahead of the flame are studied in each regime. Forward heat transfer though the solid fuel becomes more important in the Chemical Kinetic and Near Quiescent Regimes, a previously unknown result. The rate and path of forward heat transfer is found to depend strongly on simplifying assumptions and the flame anchor location. These results explain the relationship between previous analytical and experimental forward heat transfer results. A dimensionless criterion predicting the fuel thickness at which transition from thermally thick to thermally thin is developed which compares well with experimental and computed results. Finite-rate gas-phase chemical kinetics are found to be the cause of the super-thin regime of flame spread. A formula for the limiting flame spread rate in this regime is developed. Correlation of computed spread rates with the Damkohler number is revisited. Uncertainty in residence time due to uncertainties in characteristic velocity and gas-phase properties is found to be the cause of spread in the correlation. The Damkohler number alone explains variations in many parameters although it alone cannot explain changes in gas-phase activation energy. The boundary between the Near Quiescent and Thermal Regime is quantified using a dimensionless radiation number. A new extinction limit for thick fuels in the Near Quiescent Regime is discovered. Radiative losses cause the flame to grow small and spread so slowly that sufficient oxygen is not available to sustain the flame. Recent experimental results confirm this conclusion.

Download or read book A Model of Flame Spread Over a Thin Solid in Concurrent Flow with Flame Radiation written by Ching-Biau Jiang and published by . This book was released on 1995 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Model Calculation of Concurrent Flame Spread Over a Thin Solid in a Flow Tunnel written by Hsin-Yi Shih and published by . This book was released on 1997 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Numerical Modeling of Turbulent Combustion and Flame Spread written by Zhenghua Yan and published by . This book was released on 1999 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: Theoretical models have been developed to address several important aspects of numerical modeling of turbulent combustion and flame spread. The developed models include a pyrolysis model for charring and non-charring solid materials, a fast narrow band radiation property evaluation model (FASTNB) and a turbulence model for buoyant flow and flame. In the pyrolysis model, a completely new algorithm has been proposed, where a moving dual mesh concept was developed and implemented. With this new concept, it provides proper spatial resolution for both temperature and density and automatically considers the regression of the surface of the non-charring solid material during its pyrolysis. It is simple, very efficient and applicable to both charring and non-charring materials. FASTNB speeds up significantly the evaluation of narrow band spectral radiation properties and thus provides a potential of applying narrow band model in numerical simulations of practical turbulent combustion. The turbulence model was developed to improve the consideration of buoyancy effect on turbulence and turbulent transport. It was found to be simple, promising and numerically stable. It has been tested against both plane and axisymmetric thermal plumes and an axisymmetric buoyant diffusion flame. When compared with the widely used standard buoyancy-modified k-e model, it gives significant improvement on numerical results. These developed models have been fully incorporated into CFD (Computational Fluid Dynamics) code and coupled with other CFD sub-models, including the DT (Discrete Transfer) radiation model, EDC (Eddy Dissipation Concept) combustion model, flamelet combustion model, various soot models and transpired wall function. Comprehensive numerical simulations have been carried out to study soot formation and oxidation in turbulent buoyant diffusion flames, flame heat transfer and flame spread in fires. The gas temperature and velocity, soot volume fraction, wall surface temperature, char depth, radiation and convection heat fluxes, and heat release rate were calculated and compared with experimental measurements. In addition to provide comprehensive data for comparison, experiments on room corner fire growth were undertaken, where the gas temperature, solid fuel surface temperature, radiative heat flux, char depth and heat release rate were all measured.

Download or read book An Experimental Determination of the Effect of an Opposed Buoyant Flow on Flame Spread Rate Over Solid Combustibles written by David C. Winchester and published by . This book was released on 1980 with total page 214 pages. Available in PDF, EPUB and Kindle. Book excerpt: