An updated kinetic mechanism for aluminum gas-phase combustion in oxygen and steam environments

Abstract

Aluminum (Al), as a carbon-free energy source, features favorable characteristics regarding its production, transportation, utilization, and recyclability. The combustion of single Al particles mainly occurs as a vapor-phase diffusion flame, wherein the gas-phase combustion kinetics plays an important role. However, the understanding of the kinetics is still limited and rate constants for the same reactions implemented in the mechanisms are quite different. Building on a previous review and analysis work of available Al gas-phase combustion mechanisms in the literature, this paper presents an updated selection of rate constants for the Al/O₂/H₂O system based on both experimental and theoretical studies from published literature. The performance of the proposed mechanism is evaluated against experimental data and other mechanisms using an in-house boundary layer resolved model to simulate the steady-state combustion stage of a liquid Al droplet. Distinct reaction pathways in different mechanisms are explored and discussed. Global sensitivity analysis is conducted to identify the important elementary reactions that affect the prediction of the flame structure. The proposed mechanism provides more consistent predictions of flame parameters under various conditions compared to existing mechanisms. With the attempt to unify existing mechanisms and combine latest experimental and theoretical studies on the rate constants, the proposed mechanism provides a reliable framework for Computational Fluid Dynamics (CFD) modelers to use in large-scale simulations. Further refinement of Al combustion kinetics necessitates additional experimental validation and quantum chemistry analysis.