Nguyen, Bich-Diep ; Braig, Daniel ; Scholtissek, Arne ; Ning, Daoguan ; Li, Tao ; Dreizler, Andreas ; Hasse, Christian (2024)
Ignition and kinetic-limited oxidation analysis of single iron microparticles in hot laminar flows.
In: Fuel, 371
doi: 10.1016/j.fuel.2024.131866
Article, Bibliographie

Abstract

The ignition temperature is closely linked to the reaction front speed in iron dust flames, a crucial target quantity when trying to predict the characteristics of such flames. To this end, the ignition of iron microparticles is analyzed in this paper by means of single particle simulations which are compared with recent ignition experiments by Ning et al. Different particle sizes and oxygen concentrations in the gas phase are investigated, since iron particles in a dust flame are polydisperse and experience vastly different oxygen atmospheres. Several modeling approaches have been proposed for the reaction kinetics governing the ignition process and in this work, two of the most widely used models are considered: one describing the kinetics as a surface reaction and the other assuming the diffusion of iron cations through the solid oxide layer as the rate-limiting mechanism. The onset of the particle oxidation can be characterized by the solid-phase oxidation time (SOT) during which inert heating and thermal runaway of the iron microparticles occur. Therefore, the SOT allows for the assessment of the predictive capabilities of the models regarding ignition. With this background, it is the objective of this work to gain insights into the rate-limiting mechanisms controlling the ignition and to assess, whether the state-of-the-art models require further calibration. Uncertainty assessment is performed for the SOT predictions reflecting experimental uncertainties for particle sizes. It is found that the current models mostly underpredict the SOT which is a strong indication that the limiting factors for all cases of iron oxidation are still not sufficiently well understood. The experimental measurements indicate that the SOT depends on the oxygen concentration of the surrounding gas. Possible rate-limiting mechanisms are discussed and new kinetics parameters are proposed from model calibration with the experimentally measured SOT. The ignition temperature of the calibrated model is compared with measured ignition temperatures from various experimental studies in the literature and reasonable agreement is found.

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