Relationship investigation between quantitative cellular information and self-acceleration of lean hydrogen-air spherical premixed flame

Abstract

Due to the high diffusivity of hydrogen molecules, lean hydrogen-air premixed flames are more prone to cellular instability during combustion. This instability is known to often lead to self-acceleration of flame propagation, with the flame speed closely related to the cellular area on its surface. In this study, the relationship between quantitative cellular information and self-acceleration of lean hydrogen-air premixed spherically expanding flames was systematically analyzed under various initial temperatures. The focus was on equivalence ratios of 0.4, 0.5, and 0.6, with initial temperatures set at 300 K, 360 K, and 400 K. Quantitative cellular information, including cell number, two- and three-dimensional average cell area, and total cellular flame area, was obtained using an in-house developed image processing program. Based on these quantitative data, the ratio of cellular flame surface area to laminar flame surface area was calculated, and the fractal dimension of the flame front along with the flame self-acceleration exponent was derived. Results indicate that with increasing equivalence ratio and initial temperature, the onset of cellular instability is delayed, while the self-acceleration exponent gradually increases with flame propagation, eventually stabilizing in the range of 1.2–1.4 after full cellularization. Under leaner conditions and lower initial temperatures, flames exhibited a higher self-acceleration exponent. The self-acceleration exponent obtained from the 3D-reconstructed cellular flame area offers a new perspective for developing accurate models of self-accelerating spherically cellular flame propagation, with significant potential applications in hydrogen combustion and explosion safety.