Heat release and transfer of premixed propane/air flames in high g-load centrifugal force fields

Abstract

Rapid combustion and propagation are crucial for energy conversion and utilization equipment, such as power plants and thrust engines. High g-load in centrifugal flow fields has been demonstrated to be able to elevate turbulent flame speed. However, more details of flame behaviors in strong centrifugal force fields still need to be investigated. This paper focuses on flame bubble behaviors and related aspects by conducting Large Eddy Simulations (LES) of high g-load centrifugal flames stabilized by a backward step in an annual combustor. A centrifugal force was produced by setting different circumference inlet velocities (0 ms/, 4 m/s, 8 m/s, 12 m/s and 16 m/s) while axial velocity was constant (12 m/s). Wall-adapting Local Eddy-viscosity (WALE) model was used as the subgrid-scale model. Flamelet Generated Manifold (FGM) model and a 31-species and 107-step propane/air reaction mechanism were used for combustion modeling. The centrifugal body force exerted on flame bubbles and cold gas parcels is found to be able to make them move oppositely in the radial direction, and thus makes the flame surface more wrinkled. This effect leads to reinforced heat exchange between hot burned gas and cold fresh mixture. The consequent results are not only that the flame propagation speed is increased and the flame zone is broadened, but also that the local heat loss is enhanced, which leads to a weaker local heat release rate and might even lead to flame extinction. Additionally, the time-averaged flame front consists of a preheating zone and a reaction zone, along with a centrifugal-force-induced heat transfer from the post-flame zone to the cold fresh mixture.