Combustion-Controlled Thermal Loading and Non-Isothermal Spinel Growth in MgO–Al$_{2}$O$_{3}$ Systems under Premixed Strained Syngas/Air Flames

High-temperature solid-state reactions are highly sensitive to thermal loading, requiring precise control of temperature magnitude and evolution. In the present work, a thermodynamically consistent multiscale framework is developed to simulate nonisothermal solid-state reactions induced by a laminar strained premixed CO/H$_2$/air flame. The thermal field within a MgO–Al$_2$O$_3$ material system is controlled through modulation of the imposed flame strain rate, while the growth kinetics of magnesium aluminate spinel (MgAl$_2$O$_4$) are described using a Thermodynamic Extremal Principle (TEP)-based nonequilibrium model coupled to CALPHAD. The results show that decreasing the flame strain rate provides an effective and physically possible strategy to regulate the internal material temperature under homogeneous conditions. Different flame strain-rate transition times lead to different heating profiles and significantly influence the evolution of spinel thickness. Faster heating results in thinner spinel layers despite higher instantaneous growth rates, which are attributed not only to temperature-dependent diffusion but also to enhanced thermodynamic driving forces arising from the expansion of the spinel stability region at elevated temperatures. ... mehrStochastic fluctuations in the flame strain rate are shown to have negligible impact on the material temperature evolution due to thermal inertia, indicating robustness of the proposed thermal control strategy. The proposed framework establishes a direct link between controllable combustion parameters and solid-state reaction, providing a foundation for combustion-driven thermal engineering of advanced ceramic systems.