Laminar flame propagation in supercritical hydrogen/air and methane/air mixtures

The propagation of laminar hydrogen/air and methane/air flames in supercritical conditions was computationally simulated for the planar flame configurations, incorporating descriptions of supercritical thermodynamics and transport as well as high-pressure chemical kinetics. The inaccuracies associated with the use of ideal gas assumptions for various components of the supercritical description were systematically assessed with progressively more complete formulation. Results show that, for hydrogen/air flames, the laminar flame speeds at high pressures increase due to the non-ideal equation of state (EoS), and is mainly due to the density modification of the initial mixture. Including the thermodynamic properties of heat capacity reduces the flame speed because of the correspondingly reduced adiabatic flame temperature. Transport properties were found to have small effect because of the inherent insensitivity of the laminar burning rate to variations in the transport properties. For methane/air flames, the use of recently reported high-pressure chemical kinetics considerably affects the laminar flame speed, even for the same flame temperature.