TIME: 3:30 PM

LOCATION: GMCS 314

SPEAKER: Christopher Douglas, 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 reactive 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.

HOST: TBD