Spatiotemporally Resolved Multi-Scalar Measurements of Methane Tulip Flames in a Square Channel

Abstract: Understanding the propagation dynamics of premixed flames in confined spaces is important for fire safety in gas pipelines and for optimizing modern internal combustion engines. In sufficiently long channels, premixed flames routinely develop tulip flame structures, yet the dominant mechanism remains elusive, and quantitative data on the evolution of flame morphology and key scalar fields are critically needed to improve the explanation, characterization, and modeling of tulip flame dynamics. In this study, premixed flames of a stoichiometric methane/air mixture were investigated in a square channel at a reduced pressure of approximately 0.3 atm. Time-synchronized, multi-plane, dual-color PLIF measurements yielded a spatiotemporally resolved 3-D dataset of key scalar fields, including temperature and OH concentration, throughout the formation and evolution of the tulip structure. Significant heat loss across the walls counteracted the heat released by combustion, producing a near-constant-pressure environment throughout the experiment. A super-equilibrium distribution of OH concentration was observed in the thermal boundary layers, suggesting that thermal cooling dominated over chemical relaxation in those regions. Additionally, the flame-front morphology at five representative times was determined using a 3-D reconstruction algorithm, from which the flame surface area was extracted. The results of this study should aid theoretical modeling and numerical simulations of premixed flame propagation dynamics in confined spaces under realistic boundary conditions.