Excess enthalpy combustion of methane-air in a novel micro non-premixed combustor with a flame holder and preheating channels

Abstract

A novel micro non-premixed combustor with a flame holder and preheating channels is developed to improve the non-premixed flame stabilization for the first time. The numerical results indeed show that the methane-air non-premixed flames can maintain stable with no flashback or pulsating flame even at the stoichiometric ratio compared to the premixed flame, which indicates that the flame stabilization in the present combustor is indeed excellent. The maximum flame temperature at each operating condition is higher than the corresponding adiabatic flame temperature. The excess enthalpy ratio (Reer) is larger at a smaller nominal equivalence ratio (ϕ) and a bigger Reynolds number (Re), and the maximum Reer reaches 36.7%. With the decrease of ϕ, the area of excess enthalpy zone increases at smaller Re (<160), but expands firstly and then shrinks at a larger Re (≥160). In addition, some new non-premixed flame propagation characteristics are found. At the larger ϕ (>0.6), the flame top presents the “Λ” shape, which is significantly different from the flame topology structure of methane/air premixed flame. The standoff distance (Sroot) between the flame root and the flame holder at the larger Re decreases firstly and then increases with the decrease of ϕ, and the anomalous and non-monotonic Sroot are both found. These interesting flame propagation features are reported for the first time for the micro non-premixed flame. Researchers can gain insight into micro non-premixed flame propagation characteristics under the competitive effect between the combustion reaction and mixed performance through the present work.