Microgravity experiments are performed to study wind-assisted flame spread over discrete fuel elements. Ultra-thin cellulose-based fuel segments are distributed uniformly in a low-speed flow and flame spread is initiated by igniting the most upstream fuel segment. Similar to continuous fuels, flame spread over discrete fuels is a continual process of ignition. Flame propagation across a gap only occurs when a burning fuel segment, before it burns out, ignites the subsequent segment. During this process, gaps between samples reduce the fuel load, increasing the apparent flame spread rate and decreasing the heat transfer between adjacent segments. The reduction in heat transfer decreases the solid burning rate. In this study, sample segment length, gap size, and imposed flow velocity are varied to study the impacts on burning characteristics, including propensity of flame spread, flame spread rate, and solid burning rate. Detailed profiles of the transient flame spread process are also presented.

Building fire, Forrest fire, and warehouse compartment fire are some of the most frequently occurring practical fire hazards in modern world. Although these types of hazards seem irrelevant from one another, they have some things in common from the perspective of fire protection engineering, in that they all have a very similar fundamental fuel-gap configuration, or discrete fuel configuration. There has been some studies in the past regarding the subject, yet it is not the most popular in the field. Furthermore, there is even fewer, if not any, numerical analysis done to fires in discrete fuel configuration. Discrete fuel arrangements represent some practical fire hazard situations, such as compartment fires in enclosed vehicles. In this study, an unsteady two-dimensional numerical model (Fire Dynamics Simulator) was used to simulate concurrent flame spreadover paper-like thin solid fuels in discrete configurations in microgravity (0g, where a20cm/s flow is imposed) and in normal gravity (1g). An array of ten 1cm-long fuel segments is uniformly distributed in the flow direction (0g) or in the vertical direction (1g).A hot spot ignition source is applied at the upstream leading edge of the first fuel seg-ment. The separation distance between the fuel segments is a parameter in this study, ranging from 0 (corresponding to a continuous fuel) to 3cm. Using this setup, the spread rate of the flame base and the fuel burning rate were studied. The spread rate in 1g and 0g increases with increasing separation distance. This is due to the gaps in the discrete fuel that force the flame base to jump to the subsequent fuel segment when the upstream segment burns out. On the other hand, the fuel burning rate behaves differently in 1g versus 0g. At a flow velocity of 20 cm/s in 0g, the flame reaches a limiting length and the flame length is approximately the same ( 4cm) for all fuel configurations. Therefore, as the separation distance increases, the preheating length (the fuel area exposed to the flame) decreases, resulting in a smaller burning rate. In 1g, the buoyancy driven flow accelerates as it rises, resulting in a longer flame as the separation distance increases. In all simulated configurations, the flame extends to the last fuel segment before the first fuel segment burns out and the flame spans the entire set of fuel segments. However, flame standoff distance reduces at the gaps between fuel segments, and in some con-figurations, the flame breaks into multiple flamelets. The shorter standoff distance and intense burning at each flamelet base result in a larger total burning rate as the separation distance increases.

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.

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.