Direct measurements of hydrogen–air flame quenching distances in a converging channel under various wall temperatures

Abstract

Flame quenching distances are fundamental data for combustion safety. In this study, we systematically investigate the quenching distances of hydrogen–air flames, with a particular focus on the influence of wall temperature, which mimics the practical boundary conditions in burners but has been overlooked in previous studies. The experiment used a converging rectangular channel with an accurately controlled gap spacing. Flame propagation was observed using Schlieren imaging, and the wall temperature was systematically changed and maintained by placing the channel within a hot air co-flow column. The flame quenching distance was determined by analyzing the channel gap width at the location where the flame front ceased to propagate. Measurements were conducted over a wide range of equivalence ratios (0.4–2.0) and wall temperatures from 20 °C to 282 °C. At room temperature, the measured quenching distances show excellent quantitative agreement with historical data, with a minimum value of approximately 0.51 mm occurring slightly rich of stoichiometry. Increasing wall temperature consistently reduces the quenching distance across all equivalence ratios, shifting the minimum quenching distance to approximately 0.40 mm at the highest tested temperature. The absolute reduction is most pronounced for very lean and very rich mixtures. The measured data generally follow the theoretical scaling proposed by Spalding, with the square of the quenching distance decreasing linearly with wall temperature. Novelty and significance statement: This study presents the first direct measurements of hydrogen–air flame quenching distances in a converging channel under systematically varied wall temperatures. Unlike prior work, which largely neglected wall temperature effects, this study quantitatively demonstrates that elevated wall temperature reduces quenching distance and qualitatively characterizes effects of equivalence ratio and wall temperature on quenching interface morphologies. By establishing wall temperature as a critical parameter governing hydrogen–air flame quenching, this study fills a key gap in combustion safety research. The findings provide quantitative and morphological benchmarks directly applicable to the design of hydrogen combustion systems operating under realistic elevated-temperature conditions, strengthening the physical foundation needed for safe hydrogen energy adoption.