Combustion heat flux estimation for design of carbon fiber-based thermal protection systems

Thermal protection systems are essential to withstand the large aerothermal loads of hypersonics flow environments. This approach is investigated for hypersonic propulsion using scramjets, where the combustor walls must be insulated against hot gaseous combustion products in addition to high temperatures from supersonic flow deceleration. Weight is key for flight, so an attractive option is protection with light-weight carbon-phenolic composite materials, where the phenolic resin degrades by pyrolysis reactions, producing gases that flow toward the surface. The analysis of flame-exposed lightweight carbon fiber insulators is performed with experiments and numerical simulations of a controlled environment. Our setup uses the McKenna flat flame burner, which creates a steady, laminar flame where combustion products interact with test materials. This configuration allows a controlled assessment of fluid-wall interaction and consequent degradation of the test samples without the complexity of supersonic turbulent mixing. Initial validation of a coupled combustion flow/material model is presented.