Numerical analysis of the stability of iron dust Bunsen flames

Abstract

This article presents numerical simulations of the response of an iron dust Bunsen flame to abrupt changes in particle seeding. A validated numerical model is employed to investigate the effect of particle seeding fluctuations on flame stability. Simulations are conducted for the Bunsen setup in both right-side-up and upside-down configurations. No significant differences in flame response are identified in flame stability between the right-side-up and upside-down configurations. The flame response does not show signs of flame wrinkling or activation of other intrinsic instabilities. As a result, the flame is surprisingly robust to abrupt changes in particle loading. We hypothesize that the robustness of the flame to imposed fluctuations is due to the lack of a feedback mechanism between the burned temperature and the heat release rate. This mechanism is present in conventional, chemistry-driven, gaseous flames. However, such a mechanism is absent in iron dust flames because the combustion of individual iron particles is limited by oxygen diffusion, which is insensitive to temperature. The high robustness of the flame appears to contradict experimental observations, where flames are found to be highly unstable, which raises questions about the mechanism underlying the instability of experimental flames.