Three-dimensional numerical investigation of flashback in premixed hydrogen flames within perforated burners

Abstract

Predicting flashback represents a pivotal challenge in the development of innovative perforated burners for household appliances, especially for substituting natural gas with hydrogen as fuel. Most existing numerical studies have utilized two-dimensional (2D) simulations to investigate flashback in these burners, primarily to reduce computational costs. However, the inherent complexity of flashback phenomena suggests that 2D simulations may inadequately capture the flame dynamics, potentially leading to inaccurate estimations of flashback limits. In this study, three-dimensional (3D) simulations are employed to examine the impact of the actual slit shapes on the flashback velocities of hydrogen-premixed flames. Steady-state simulations are conducted to compute flashback velocities for three equivalence ratios (ϕ=0.6, 0.8, and 1.0), investigating slits with fixed width W and varying length L. Additionally, transient simulations are performed to investigate the flashback dynamics. The results are compared with those from 2D configurations to assess the reliability of the infinite slit approximation. For stable flames, 2D simulations underpredict the burner plate temperature compared to slits with lengths typical of practical devices but match the 3D results as L→∞. Conversely, flashback velocities are consistently underpredicted in 2D simulations compared to 3D simulations, even as L→∞. This is due to the critical role of the slit ends in flashback dynamics, where favorable aerodynamics, preferential diffusion, the Soret effect, and higher preheating due to a higher surface-to-volume ratio trigger the initiation of flashback in those regions. These findings underscore the necessity of employing 3D simulations to accurately estimate the flashback velocities in domestic perforated burners. Novelty and significance statement This study presents a novel investigation into how finite slit lengths affect the critical flashback velocities in hydrogen-fueled perforated burners, using three-dimensional simulations. Our findings indicate that two-dimensional configurations, which are widely used in the literature, significantly underpredict flashback velocities because they fail to capture the crucial influence of slit ends. For the first time, we show that in slits of finite length and circular holes, the combined effect of favorable aerodynamic conditions and enhanced preheating, due to the increased surface area available for heat transfer, leads to higher flashback velocities compared to infinite-length slits. Additionally, we provide the first analysis of the temporal evolution of flashback dynamics in a realistic three-dimensional configuration, demonstrating that flashback initiation occurs at the slit ends. These insights are essential for the development of advanced numerical models that can inform the design of innovative perforated burners to prevent flashback effectively.

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