A Framework for Understanding the Impact of Fuel Composition on Flame Heat Transfer to Materials

Gas turbine hot section materials experience extreme environments with high heat loads. Several recent studies in representative combustor configurations have shown that convective and radiative heat transfer contributions can vary significantly depending on flow features and fuel composition. In this work, we use a fundamental burner configuration to better understand the impact of fuel composition and material properties on heat transfer to hot section materials. A new framework allows the separation of convective and radiative contributions through heat-flux measurements, chemical kinetic modeling, and one-dimensional modeling of convective and radiative heat transfer. Material samples were mounted to a heat-flux block above a standard flat-flame McKenna burner, and heat flux was measured using a one-dimensional thermal network derived from a thermocouple array embedded in the insulated block. A large test matrix that includes variations in adiabatic flame temperature, product mole fraction of carbon dioxide, and product mole fraction of water was tested with blends of methane and hydrogen in various oxidizers. Species profiles and gas properties downstream of the burner were calculated with Cantera's burner-stabilized flame model. Convective contributions were evaluated using a heat-transfer correlation that matches the burner's flow regime. Radiation from the sample surface was calculated using a literature emissivity estimate and the Stefan-Boltzmann law applied to the resistance-network surface temperature. With these measurements and models, heat-flux components were calculated for several CH4-H2 blends while holding equilibrium gas properties constant. Net heat flux was most sensitive to gas temperature, followed by water vapor content, and then carbon dioxide content. The results demonstrate both the viability of the proposed framework for separating heat-flux components, which will be used for future experimental design.