Suppression of intrinsic instabilities by strain in thermodiffusively unstable hydrogen flames

Abstract

This study evaluates the effect of strain on the dynamic response of three-dimensional, thermodiffusively unstable lean premixed hydrogen flames. The analysis combines results obtained using a Sivashinsky-type weakly non-linear model in a stagnation-point flame configuration with fully non-linear, high-fidelity numerical simulations featuring detailed chemistry and transport in a counterflow reactants-to-products setup. The flame response to a polychromatic perturbation imposed along the third or ‘extruded’ dimension of the two strained configurations is evaluated in the linear regime. Results from both approaches reveal a stabilising effect with increasing strain, ultimately leading to the stabilisation of all the perturbation modes monitored at sufficiently high strain rate, which is linked to a strain-induced local flow redistribution in correspondence of positively and negatively curved flame fronts in the counterflow configuration. By integrating our previous findings in two-dimensional counterflow configurations (Porcarelli et al , Proc. Combust. Inst. 41 (2025) 105906) with the three-dimensional results presented here, we demonstrate for the first time that the onset of intrinsic flame instabilities in thermodiffusively unstable mixtures can be suppressed at sufficiently high strain rate conditions regardless of the direction of the imposed perturbation. Novelty and significance statement This study performs for the first time a linear stability analysis of three-dimensional, thermodiffusively unstable lean premixed hydrogen flames in strained configurations using both a weakly non-linear model and a fully non-linear model with detailed chemistry and transport. It is demonstrated that sufficiently high applied strain rate tends to suppress the onset of intrinsic instabilities in thermodiffusively unstable lean premixed hydrogen flames regardless of the direction of the imposed perturbation. This finding advances our understanding on the response to strain of lean premixed hydrogen flames, and suggests that strained configurations offer a viable strategy to control such flames in practical carbon-free and low-NO_x combustion systems.