Structure and propagation of spherical turbulent iron-methane hybrid flame at elevated pressure

In this communication we demonstrate the role of turbulence intensity in the dual-front structure and self-similar propagation of spherical turbulent iron-methane hybrid flames. We first show that iron -methane hybrid mixture, whose iron concentration is below a critical threshold for the formation of a dust flame front in laminar or weak turbulent environment, can be burned strongly with both separated dual-front and merged single-front structures in intense turbulence. It is suggested that the formation of iron flame front would be attributed to local iron concentration accumulation by preferential sampling with near-unity Stocks number ( St ), heat transfer enhancement of iron particles to fluid and mixing pro-motion of iron particles with oxidants by strong turbulence. The propagation of iron front falls behind the methane front in the leading segments which is promoted by flame stretch for sub-unity Lewis number ( Le ), thus the separated dual-front structure occurs. Furthermore, the strong self-similar propagation of spherical turbulent iron-methane hybrid flame was observed under different turbulence intensities (urms). Mechanistically, such strong self-similar propagation of the hybrid flame is the consequence of the couple effects of flame mode transition at high urms with near-unity St and differential diffusion for sub-unity Le .& COPY; 2023 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

In this study, the role of turbulence intensity in the dual-front structure and self-similar propagation of spherical turbulent iron-methane hybrid flames is demonstrated. It is found that intense turbulence can cause the strong burning of iron-methane hybrid mixture with separated dual-front or merged single-front structures. The formation of iron flame front is attributed to local iron concentration accumulation, enhanced heat transfer of iron particles, and mixing promotion of iron particles with oxidants by strong turbulence. Additionally, strong self-similar propagation of the hybrid flame is observed under different turbulence intensities, which is influenced by flame mode transition and differential diffusion.