Burning and Extinction of a Laser‐Ignited Carbon Particle in Quiescent Mixtures of Oxygen and Nitrogen

Abstract

Experimental data on the burning mode and lifetime, on the surface temperature, and on the spontaneous extinction of a laser‐ignited particle of electrode carbon (50–200μ) in quiescent mixtures of oxygen and nitrogen at room temperature are presented. The test variables were the oxygen mass fraction (0.5–1) and the pressure (0.5–3 atm) of the mixture. High speed cinemicrography of the burning particle showed that the visible combustion zone was restricted to the surface. Two theoretical models, one neglecting the dissociation of oxygen and the other including it approximately, are developed in order to explain the extinction phenomenon. Comparison of the extinction results computed from these models with the data indicates that the model neglecting dissociation is the preferred one. Based on this model it is shown that the kinetics of oxidation of electrode carbon in the temperature range 2000°–3500°K can be represented by an effective Arrhenius surface oxidation reaction producing CO and having an activation energy of 18 kcal/mole and an order in the range 0.5–1.

Modeling and experimental studies on combustion characteristics of porous coal char: Volume reaction model

“…Even combustion in ignited regime was found to undergo extinction near the end as the specific surface area of the coal char decreased drastically. This was in line with experimental observations of Ubhayakar and Williams [41]. The burnout time was found to attain a minima with respect to the particle radius due to shift in combustion regime from extinction to ignition, which was in conformity with the observations of Sundaresan and Amundson [21] for combustion of carbon particles.…”

“…10). Similar ignition in the combustion regime and extinction near the end were observed experimentally by Ubhayakar and Williams [41].…”

Thermally induced structural changes in coal combustion. Final report

“…The time dependent equ1tion (3) can therefore be written as (9) The term H1 is the heat gain from absmption of the laser energy.…”

Critical condition related to the activation of solid fuel particles; comparisons with experimental results for char combustion in a quiescent environment

“…Therefore, under an assumption of quasi-steadiness in the gas phase, formulation has been conducted, as described in the previous works [34][35][36][37][38][39], so that only the final solution is presented herein, with adhering almost completely to the model definition, formulation, and nomenclature of Refs. [41,42].…”

“…Unfortunately, however, it has been rare for those results to be compared with theoretical results, in spite of the fact that such formulations [34][35][36][37][38] for a spherical particle have widely been introduced in many textbooks. Furthermore, it has even been suggested that small particles may be considered to burn under quiescent condition [39].…”