Experimental Observations on the Thermal Degradation of a Porous Bed of Tires

In this paper, an experimental study on the forward combustion of a bed of tires and refractory briquettes is presented. Temperature measurements within the reactor were obtained as a function of time as well as the evolution of the fuel bed. The products of combustion were cooled down and usable liquid fuel was recovered and measured. The reaction was found to become unstable for fuel concentrations lower than 50%. The results show that the airflow and tire concentration define different modes of combustion while the reaction remains oxygen limited. Oil production is maximized when an increase in airflow leads to a transition from a rate-limited reaction to a heat transfer-limited propagation. Variation of the tire concentration shows the importance of the inert in achieving high conversion rates

Modeling of One-Dimensional Smoldering of Polyurethane in Microgravity Conditions

Results are presented from a model of forward smoldering combustion of polyurethane foam in microgravity. The transient one-dimensional numerical-model is based on that developed at the University of Texas at Austin. The conservation equations of energy, species and mass in the porous solid and in the gas phases are numerically solved. The solid and the gas phase are not assumed to be in thermal or in chemical equilibrium. The chemical reactions modeled consist of foam oxidation and pyrolysis reactions, as well as char oxidation. The model has been modified to account for new polyurethane kinetics parameters and radial heat losses to the surrounding environment. The kinetics parameters are extracted from thermogravimetric analyses published in the literature and using Genetic Algorithms as the optimization technique. The model results are compared with previous tests of forward smoldering combustion in microgravity conducted aboard the NASA Space Shuttle. The model calculates well the propagation velocities and the overall smoldering characteristics. Direct comparison of the solution with the experimental temperature profiles shows that the model predicts well these profiles at high temperature, but not as well at lower temperatures. The effect of inlet gas velocity is examined and the minimum airflow for ignition identified. It is remarkable that this one-dimensional model with simplified kinetics is capable of predicting cases of smolder ignition but with no self-propagation away from the igniter region. The model is used for better understanding of the controlling mechanisms of smolder combustion for the purpose of fire safety, both in microgravity and normal gravity, and to extend the unique microgravity data to wider conditions avoiding the high cost of space-based experiments

NUMERICAL STUDY OF FORWARD SMOLDERING COMBUSTION (in Spanish)

(in English) AbstractThis paper presents the results from the numerical study of the forward smoldering combustion process. The study is based on the transient model developed at University of Texas at Austin but extended with some modifications. In the model, the equations of conservation of energy and mass are solved. The chemistry is represented by a simplified scheme which consists of three reactions. Equations are discretized in space and solved in time. Neither thermal nor chemical equilibrium between solid and gas phases is assumed. The more important extensions made to the original model are: radiation heat transfer is included, a new ignition process is implemented and the porous structure of the solid is reconsidered. The extensions to the original model were implemented in order to predict the experimental data. The model with its extensions has been calibrated at a higher inlet air velocity and validated. The results show that the model predicts reasonably well the velocity of propagation of the smoldering front.(in Spanish) Estudio numerico de combustion latente en flujo directoResumenEste articulo presenta los resultados del estudio numerico del proceso de combustion latente en flujo directo. La combustion latente es una reaccion exotermica sin llama que se propaga en combustibles porosos. El estudio se basa en el modelo transitorio desarrollado en la Universidad de Texas en Austin, pero ampliado con varias modificaciones. En el modelo se resuelven las ecuaciones de conservacion de la energia y la masa. La cinetica quimica se modela con un esquema simplificado de tres reacciones. Las ecuaciones diferenciales se discretizan en el espacio y se resuelven en funcion del tiempo. El modelo no fuerza el equilibrio ni termico ni quimico entre las fases solida y gaseosa. Las modificaciones mas importantes realizadas son la inclusion de la transmision del calor por radiacion, la incorporacion de un nuevo proceso de ignicion y la reconsideración de la microestructura de los poros del solido. El objetivo de las ampliaciones es completar y adaptar el modelo a los experimentos publicados para comparar resultados. El modelo se calibra de nuevo a una velocidad mayor del aire de entrada. Los resultados muestran que se estima adecuadamente la velocidad de propagacion del frente de combustion