Flash-back, blow-off, and symmetry breaking of premixed conical flames
Duke University
Abstract
Ongoing concerns about combustion-related greenhouse gas emissions have motivated substantial efforts to integrate alternative fuels such as hydrogen (H2) into existing energy infrastructure. Nonetheless, H2 is characterized by strong reactivity and remarkably high mass diffusion rates, leading to complex combustion dynamics that pose significant operational challenges for H2 as an alternative fuel. More specifically, lean premixed H2 flames feature extreme sensitivity to hydrodynamic stretch and intrinsic flame instabilities that drive intimate couplings between the flame and flow behavior. Nonetheless, the interaction and coupling of intrinsic flame dynamics with background flow gradients and boundary conditions remains poorly understood.
Motivated by these challenges, this seminar will present a global nonlinear bifurcation analysis of burner-stabilized laminar premixed conical flames in a fully-coupled framework. In it, the dynamics of flash-back, blow-off, and symmetry breaking are explored in mixtures with varying reaction rates and reactant diffusivities parameterized by the Damköhler number (Da) and the Lewis number (Le), respectively. Within this approach, the conical flame is identified as a steady solution of the low-Mach number, reacting Navier–Stokes equations that exists within a defined region of the (Le, Da) parameter plane. This region is bounded by curves of saddle–node (SN) bifurcations that correspond to spontaneous flame flash-back or blow-off, revealing how the parameters control these events. Further, the analysis shows that the conical flame experiences a sudden loss of axisymmetry via circle–pitchfork (CP) bifurcations in low-Le and high-Da parameter regimes. These bifurcations correspond to steady, three-dimensional global modes describing steady polyhedral or tilted flame structures, each associated with a distinct physical amplification mechanism and azimuthal periodicity. Finally, a center manifold reduction is used to elucidate the weakly-nonlinear dynamics governing the emergence of these structures and relate them to experimental observations. Overall, these results shed new light on the fundamental flame–flow interactions that control the behavior of burner-stabilized flames across a large range of Le and Da, including those relevant to H2 combustion.
About the speaker
Dr. Christopher Douglas is an incoming Assistant Professor in the Department of Mechanical Engineering and Materials Science at Duke University starting in January 2025. He earned his Ph.D. in Mechanical Engineering from Georgia Tech in 2021. Before starting at Duke, Christopher was a Marie Skłodowska-Curie Postdoctoral Fellow jointly at École Polytechnique and TU Munich and then a postdoctoral associate at the MIT Energy Initiative. His research primarily focuses on fluid and thermal sciences, with an emphasis on flow instability, combustion dynamics, and thermoacoustics. In his work, he develops theoretical and numerical methods to analyze, understand, and control the behavior of high-dimensional nonlinear systems encountered in engineering applications including turbines, rockets, and other energy systems, as well as in diverse natural phenomena such as atmospheric mixing and supernovae. His broader research interests include energy decarbonization and pollutant emissions abatement, with particular attention to potential alternative energy carriers like hydrogen and ammonia.
Christopher is actively seeking graduate students and postdocs for the 2025 calendar year. If interested, please reach out and detail your past and future interests.
