Unsteady non-premixed methane/oxygen flame structures at supercritical pressures

Unsteady non-premixed flame structures of methane/oxygen mixtures are investigated at supercritical pressures, representative of liquid rocket engines combustion chamber operating conditions. A general- fluid for- mulation of the flamelet equations is used and deviations from ideality of the thermodynamic properties are taken into account by means of a computationally efficient cubic equation of state written in a general three-parameter fashion. The effects of pressure and scalar dissipation rate are investigated in the context of prototypical unsteady laminar flame configurations, such as autoignition and re-ignition/quenching. In auto-igniting flamelets, real gas effects are observed to influence different flame regions depending on the thermodynamic pressure. Moreover, the mixture ensuing from methane oxidation is never observed to reach a saturated (two-phase) thermodynamic region. Re-ignition and quenching phenomena are analyzed using a time dependent forcing function for the scalar dissipation rate, in order to investigate the response of the real gas flame structures to typical turbulent p erturbations. The role of pressure on the critical strain values that a real gas laminar flame can sustain without quenching is investigated and compared to its ideal gas counterpart.