Numerical study of the effect of burnout on the ignition characteristics of polymer under local heating

Abstract

This paper presents the results of a numerical study of the effect of burnout on the ignition delay of a typical thermoplastic polymer (polymethylmethacrylate) by a metal particle heated to a high temperature. The initial temperature of the energy source was varied from 960–1150 K. Three ignition modes of the polymer can be distinguished according to the temperature of the heat source, ignition delay, and the position of the ignition zone in the vicinity of the hot particle. It is found that under local heating conditions, the burnout of the heated region of the near-surface layer of the polymer has an insignificant effect (less than 5%) the increase in the basic characteristic of the process—the ignition delay. At the time of initiation of combustion, the degree of thermal decomposition of the polymer (degree of conversion) does not reach even 15% in the section corresponding to the maximum heat flux from the heat source. It is shown that the ignition delay increases more significantly when accounting for the temperature dependence of the thermal properties of polymethylmethacrylate than when accounting for the burnout factor. The induction period is increased by 15–25% due to an increase in the accumulating capacity of the polymer and heat transfer rate from the heated region of the near-surface layer into the depth of the material.