MODELING OF IGNITION OF FLAMMABLE ATMOSPHERES BY RADIATION-HEATED FIBROUS AGGLOMERATES

A model is presented to assist in the quantification of the ignition h azard associated with the application of optical fibre technology for sensing and control in potentially flammable atmospheres. Ignition ari ses if radiation from a fractured fibre impinges on a solid particle o r surface causing local heating. Uniform temperature and concentration s are assumed throughout the reaction Bone for simplicity, allowing re alistic and detailed kinetic schemes. Heat transfer is modelled by New tonian cooling and radiation, with convective effects assumed to be su ppressed by the fibrous nature of the most hazardous target materials. Results are presented, initially for H-2/air mixtures, in terms of a critical hot surface temperature. The variation of T-h,T-cr with mixtu re composition and the diameter of the optical beam are determined, al ong with the influence of various physical parameters characterising t he absorption and heat transfer processes. Results are also presented for 'wet' CO and di-ethyl ether oxidation. The critical temperatures a re converted to critical optical powers using a semi-empirical fit to experimental data. Despite the approximations invoked, the predicted c ritical data reproduce the main observed trends, show semi-quantitativ e agreement with experimental results and correlate with known combust ion parameters, such as the appropriate auto-ignition temperatures.