Recent cpl_fs items

A Generalized Pyrolysis Model for Combustible Solids

Wed, 23 Jul 2008 00:00:00 +0000

This dissertation presents the derivation, numerical implementation, and verification/validation of a generalized model that can be used to simulate the pyrolysis, gasification, and burning of a wide range of solid fuels encountered in fires. The model can be applied to noncharring and charring solids, composites, intumescent coatings, and smolder in porous media. Care is taken to make the model as general as possible, allowing the user to determine the appropriate level of complexity to include in a simulation. The model considers a user–specified number of gas phase and condensed phase species, each having its own temperature–dependent thermophysical properties. Any number of heterogeneous (gas–solid) or homogeneous (solid–solid or gas-gas) reactions can be specified. Both in–depth radiation transfer through semi–transparent media and radiation transport across pores are considered. Volume change (surface regression or swelling/intumescence) is handled by allowing the size...

A Generalized Pyrolysis Model for Simulating Charring, Intumescent, Smoldering, and Noncharring Gasification

Mon, 28 Aug 2006 00:00:00 +0000

This paper presents a generalized pyrolysis model that can simulate the gasification of noncharring, charring, and intumescent materials, as well as smoldering in porous media. Separate conservation equations are solved for gaseous and condensed phase mass and species, solid phase energy, and gas-phase momentum. An arbitrary number of gas-phase and condensed-phase species can be accommodated, each having its own temperature-dependent thermophysical properties. The user may specify any number of solid to gas, solid to solid, or solid + gas to solid + gas reactions of any order. Both in-depth radiation transfer through a semi-transparent medium as well as radiation transport across pores are considered, and melting is modeled using an apparent specific heat. All volatiles generated inside the solid escape to the ambient with no resistance to flow unless the pressure solver is invoked to solve for the pressure distribution in the solid, with the resultant flow of volatiles calculated...

Computational Model of Forward and Opposed Smoldering Combustion with Improved Chemical Kinetics (PhD. Thesis)

Mon, 19 Dec 2005 00:00:00 +0000

A computational study has been carried out to investigate smoldering ignition and propagation in polyurethane foam. The one-dimensional, transient, governing equations for smoldering combustion in a porous fuel are solved accounting for improved solid-phase chemical kinetics. A systematic methodology for the determination of solid-phase kinetics suitable for numerical models has been developed and applied to the simulation of smoldering combustion. This methodology consists in the correlation of a mathematical representation of a reaction mechanism with data from previous thermogravimetric experiments. Genetic-algorithm and trail-and-error techniques are used as the optimization procedure. The corresponding kinetic parameters for two different mechanisms of polyurethane foam smoldering kinetics are quantified: a previously proposed 3-step mechanism and a new 5-step mechanism. These kinetic mechanisms are used to model one-dimensional smoldering combustion, numerically solving...

Ignition of Combustion Modified Polyurethane Foam

Thu, 27 Oct 2005 00:00:00 +0000

Results are presented from an experimental study on the ignition of the combustion modified (fire retarded) polyurethane foam Pyrell® (35.3 kg/m3 and 64.0 kg/m3) in elevated oxygen concentrations, ranging from 30% to 60%. The samples are exposed to an external flow and variable radiant heat flux on one face, and insulated on the other faces. The experiments show that Pyrell undergoes a weak smoldering reaction that requires significant assistance in the form of external heat input in order to propagate. The results also show that given sufficient oxygen and radiant heat flux, the smoldering reaction can produce enough volatile fuel and heat to trigger a gas phase ignition, i.e. a transition from smoldering to flaming, in pores in the char region. The experiments also indicate that high-density Pyrell is more ignitable than low-density Pyrell, which could be explained by the greater solid surface area for smoldering reactions to take place.

Bidimensional Numerical Model for Polyurethane Smoldering in a Fixed Bed

Fri, 26 Aug 2005 00:00:00 +0000

Smoldering combustion is described as an exothermic superficial heterogeneous-reaction that can propagate in the interior of porous fuels. Smoldering is generally an incomplete combustion reaction, which leaves behind a porous char that contains significant amounts of unburned fuel. If compared to flaming combustion, the heat release and the temperature characteristics of smoldering are low and its propagation is a slow process. Besides its characteristics of a weak combustion process, smoldering poses serious risk to fire safety; it is a common fire initiation scenario, because it is difficult to detect as, it can go unnoticed for long periods of time, It yields a high conversion of fuel to toxic products, and it can suddenly switch to flaming combustion. The propagation of the smoldering front is usually controlled by two factors: oxygen availability and heat losses. However it’s the result of several interacting mechanisms, such as chemical reactions (pyrolysis and oxidation),...