The purpose of this thesis is to simulate the downward flame spread over thin fuel (Cellulose and Polymethylmethacrylate) in a natural convection environment. Flame spread over thermally thin fuels in quiescent and opposed-flow environment condition is studied. The study of the flame geometry, size of domain, grid points in x and y directions and boundary conditions are considered. For PMMA fuel comparison of the computational and experimental result for quiescent environment is performed. Effect of fuel half thickness, opposed flow velocity, ambient oxygen concentration and ambient pressure level on the flame spread rate was studied. Comparison of flame spread rate of complete combustion model, equilibrium model and experiments with different half thicknesses for PMMA and cellulose was performed. For cellulose fuel velocity fields and pressure field plots are plotted to understand the flow behavior near the leading edge of the flame. Two dimensional Navier-Stokes equations were implemented in a FORTRAN code which was used for numerical simulation and later on the code is modified. A Matlab code is implemented for plotting the pressure field, temperature field, reaction rate contours, fuel mass fraction and other kind of plots.

This dissertation is an investigation into the effects of natural convection on the combustion process of a spreading flame in a gravitational environment. The flame is spreading into an opposing flow of oxidizer over a solid fuel. This is approached as a steady state problem with coordinates fixed at the tip of the flame. This investigation incorporates the use of experimental data, numerical simulations and a simplified approach to develop a better understanding of combustion. The focus of the material presented can be separated in two components: First, a well validated forced flow numerical model is used to evaluate flame structure for the natural convection configuration. A simplified approach is developed and compared to the numerical model for flame structure and flame spread rates in chapters 2 and 3. Critical parameters controlling flame spread such as pressure, fuel thickness, oxygen concentration, and strength of gravitational field are widely varied. In the thermal regime, where this simplified approach applies, comparisons between experimental data, numerical solutions and simplified approach predictions are excellent. The numerical model is also compared to experimental data outside the thermal regime including a prediction of the regression rate of the solid fuel and gas phase characteristics. Second, a hybrid two-color pyrometry technique is developed and used to analyze flame structure for experiments in a microgravity environment. Images of flame intensity are calibrated and converted into temperature profiles for various opposed flow velocities and oxygen concentration. Numerical simulations are used to demonstrate various approximate techniques and their accuracies. The experimental images are used in conjunction with the numerical simulation to determine the temperature profiles and the partial pressure of carbon dioxide. Techniques are discussed on how to improve the results for future experiments by modifying the filter bandwidth selections. Through a greater understanding of the physics and controlling mechanisms for flame spread, the ability to control fire and the establishment of comprehensive guidelines for fire safety will be realized. This dissertation is another step toward that goal.

Advances in nanotechnology have boosted the development of more efficient materials, with emerging sectors (electronics, energy, aerospace, etc.) demanding novel materials to fulfill the complex technical requirements of their products. This is the case of polymeric foams, which may display good structural properties alongside functional characteristics through a complex composition and (micro)structure in which a gas phase is combined with rigid ones, mainly based on nanoparticles, dispersed throughout the polymer matrix. In recent years, there has been an important impulse in the development of nanocomposite foams, extending the concept of nanocomposites to the field of cellular materials. This, alongside developments in new advanced foaming technologies which have allowed the generation of foams with micro, sub-micro, and even nanocellular structures, has extended the applications of more traditional foams in terms of weight reduction, damping, and thermal and/or acoustic insulation to novel possibilities, such as electromagnetic interference (EMI) shielding. This Special Issue, which consists of a total of 22 articles, including one review article written by research groups of experts in the field, considers recent research on novel polymer-based foams in all their aspects: design, composition, processing and fabrication, microstructure, characterization and analysis, applications and service behavior, recycling and reuse, etc.

Flame spread over solid fuels with simple geometries has been extensively studied in the past, but few have investigated the effects of complex fuel geometry. This study uses numerical modeling to analyze the flame spread and burning of wavy (corrugated) thin solids and the effect of varying the wave amplitude. Sensitivity to gas phase chemical kinetics is also analyzed. Fire Dynamics Simulator is utilized for modeling. The simulations are two-dimensional Direct Numerical Simulations including finite-rate combustion, first-order pyrolysis, and gray gas radiation. Changing the fuel structure configuration has a significant effect on all stages of flame spread. Corrugated samples exhibit flame shrinkage and break-up into flamelets, behavior not seen for flat samples. Increasing the corrugation amplitude increases the flame growth rate, decreases the burnout rate, and can suppress flamelet propagation after shrinkage. Faster kinetics result in slightly faster growth and more surviving flamelets. These results qualitatively agreement with experiments.

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...