Elsevier

Combustion and Flame

Volume 120, Issue 3, February 2000, Pages 346-358
Combustion and Flame

Original Articles
Kinetic and fuel property effects on forward smoldering combustion

https://doi.org/10.1016/S0010-2180(99)00089-9Get rights and content

Abstract

In this paper, we present the results from a one-dimensional transient model of forward smoldering. Fuel oxidation and pyrolysis reactions as well as a char oxidation reaction are included in the model. The solid energy, solid species, gas energy, oxygen species (bulk gas and surface), and overall mass conservation equations were discretized in space using finite-difference techniques and were solved using VODE, an ordinary differential equation integrator designed for stiff equations. Local thermal and chemical nonequilibrium are allowed in this model and transfer coefficients are derived from a Nusselt number correlation. A base case is chosen to represent experimental conditions reported in the literature. The effects of inlet gas velocity, kinetic frequency factors, inlet oxygen concentration, and fuel properties such as specific heat, density, conductivity, and pore diameter were studied using this model.

Section snippets

Nomenclature

    A

    frequency factor

    c

    specific heat

    D

    diffusion coefficient

    d

    pore diameter

    Ea

    activation energy

    f

    exponent

    g

    exponent

    hA‴

    volumetric heat transfer coefficient

    hmA‴

    volumetric mass transfer coefficient

    k

    conductivity

    m

    exponent

    n

    stoichiometric coefficient

    R

    gas constant

    T

    temperature

    u

    gas velocity

    v

    smolder velocity

    V

    diffusion gas velocity

    x

    coordinate

    y

    mass fraction

Numerical model

In this study, we solve the one-dimensional time-dependent conservation equations for the solid and the gas. The domain for these computations is shown in Fig. 1. The entire domain initially consists of unreacted fuel. Air flows in at the right boundary. Ignition is initiated by holding the right boundary at a specified temperature. The reaction zone in these simulations propagates from right to left.

Results

In this section, the results from the one-dimensional simulations of forward smoldering are presented. The geometry is shown in Fig. 1. We first simulate a case similar to that studied experimentally by Torero and Fernandez-Pello [5]. Then the importance of various parameters on the smoldering process is examined. In the base case described below, we include the effects of chemistry, transport, and convective and radiative heat transfer.

Summary and conclusions

In this paper, results of one-dimensional transient simulations of forward smoldering were presented. Fuel oxidation and pyrolysis as well as a char oxidation reaction were included in this model. A base case was chosen to represent a case experimentally studied by Torero and Fernandez-Pello [5]. The numerical model confirms their interpretations of the experimental results that an endothermic pyrolysis front is followed by an exothermic oxidative front, and after some time char oxidation

Acknowledgements

This work was sponsored by the Applied Research Laboratories at the University of Texas at Austin through the Office of Naval Research.

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