Numerical study on the effect of oxygen concentration on the piloted ignition of PMMA in reduced pressure atmospheres

Abstract

<jats:sec> <jats:title content-type="abstract-subheading">Purpose</jats:title> <jats:p>This study aims to investigate the controlling mechanisms of ambient oxygen and pressure on piloted ignition of solid combustibles under external radiant heating.</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Design/methodology/approach</jats:title> <jats:p>The numerical simulation method was used to model the influence of ambient oxygen concentration on the piloted ignition of a thermally irradiated solid sample in reduced pressure atmospheres. The solid phase decomposition and gas phase kinetics were solved simultaneously.</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Findings</jats:title> <jats:p>It was determined that the elevated oxygen atmospheres resulted in a higher flame temperature and a thicker temperature profile over the solid surface. Also, increasing oxygen and reducing pressure had a similar effect in the decrease of the ignition delay time. The shorter ignition time in reduced pressure was mainly because of the decreasing of convective heat losses from the heated solid. As oxygen was reduced, however, ignition occurred later and with a greater mass loss rate because more volatiles of solid fuel at transient ignition were required to sustain a complete reaction under an oxygen-poor condition.</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Research limitations/implications</jats:title> <jats:p>The results need to be verified with experiments.</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Practical implications</jats:title> <jats:p>The results could be applied for design and assessment of fire-fighting and fire prevention strategies in reduced pressure atmosphere.</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Originality/value</jats:title> <jats:p>This paper shows the effect mechanism of ambient oxygen and pressure on piloted ignition of solid combustibles.</jats:p> </jats:sec>

Effects of the PMMA Molecular Weight on the Thermal and Thermo-Oxidative Decomposition as the First Chemical Stage of Flaming Ignition

“…In accordance with the literature review reported in [7,8], the first class of PMMA ignition models consists of condensed-phase descriptions coupled with empirical ignition criteria [9][10][11][12][13][14][15][16][17][18][19]. Another model class is based on descriptions of both the condensed and gas phases [7,8,[20][21][22][23][24][25][26][27][28][29], which do not require the use of empirical criteria. These include both simple unsteady onedimensional models, which give quantitative information on the main global parameters (e.g., ignition delay time, surface temperature, and volatile mass flux at ignition), and more advanced CFD formulations.…”

“…Instead, for spontaneous ignition, the condition of the second derivative of T gmax equal to zero is sufficient to identify the ignition time. Input data are the same used by Galgano and Di Blasi [7,8] and are listed in Table 2 [10,11,21,23,29,32,[38][39][40][41][42], except for the kinetic data (listed in Table 1). Different optical properties are also considered, corresponding to clear and black PMMA, with differences in the absorption coefficient, β s , and emissivity, e s , as reported in Table 2.…”

“…For both the spontaneous and the piloted cases, the highest sensitivity concerns the kinetics of polymer decomposition [8]. It is interesting to observe that despite the improvements in the mathematical description of the flaming ignition of PMMA when the empirical criteria of the models [9][10][11][12][13][14][15][16][17][18][19] are substituted by rigorous formulations of conservation equations for mass and energy coupled with combustion kinetics by models [7,8,[20][21][22][23][24][25][26][27][28][29], a global single-step mechanism is always used for the polymer decomposition into monomers. This kinetics is applicable only to low molecular weight samples.…”

“…In particular, the PMMA molecular weight determines important features of the decomposition mechanism that turns from a one-stage global reaction (low molecular weight) [7,[31][32][33] into a multistep process (high molecular weight) [17,34]. However, none of the literature models combine multistep decomposition kinetics with the description of either solid phase physical processes only [9][10][11][12][13][14][15][16][17][18][19] or both solid and gas processes [7,8,[20][21][22][23][24][25][26][27][28][29]. Hence, the subsequent impact of the polymer molecular weight on the ignition behavior has never been investigated.…”