Effects of Surface Structure and Properties on the Combustion Characteristics and Flame Stability of Carbonaceous Fuels
16 Pages Posted: 25 Aug 2022
Date Written: August 7, 2022
This study relates to the effects of surface structure and properties on the combustion characteristics and flame stability of carbonaceous fuels. A two-dimensional computational fluid dynamics model is developed to study the effects of wall thermal conductivity, external heat losses, and operating conditions on combustion characteristics and the steady-state, self-sustained flame stability of lean methane-air mixtures. Computational fluid dynamics simulations are conducted to gain insights into combustion performance such as reaction rates, species concentrations, temperatures, and flames. The wall thermal conductivity and exterior convective heat loss coefficient are taken as independent parameters to understand how important thermal management is. The factors affecting combustion characteristics are determined for carbonaceous fuels. The characteristics of premixed combustion and the envelopes of flame stability are studied. Comparisons between different millimeter-scale combustion systems are made. Engineering maps that delineate flame stability, extinction, and blowout are constructed. Design recommendations are made. Particular focus is placed on determining essential factors that affect the performance of millimeter-scale combustion systems. The results indicate that the cavity structure can induce recirculation of hot products, thereby improving flame stability. The wall thermal conductivity is vital in determining the flame stability of the system, as the walls are responsible for the majority of the upstream heat transfer as well as the external heat losses. Two modes of flame extinction occur: a spatially global type for large wall thermal conductivities and blowout. Large transverse and axial gradients are observed even at small scales under certain conditions. Catalytically-supported thermal combustion surmounts the mass transfer limitation, which is achieved by contacting at least a portion of the carbonaceous fuel intimately admixed with air with a solid oxidation catalyst having an operating temperature substantially above the instantaneous auto-ignition temperature of the fuel-air admixture.
Keywords: Catalytic Combustion; Carbonaceous Fuels; Gas Turbines; Engineering Maps; Design Recommendations; Mass Transfer
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