Methane combustion dynamics in PSR with detailed reaction mechanisms

Combustion phenomena, especially in industrial applications, very often involve an unsteady behavior, being really transient (f.i. ignition, accidental explosions) or because affected by unsteady phenomena (f.i. noise, turbulence). The role of a selected reaction mechanism in the correct prediction of combustion dynamics is, therefore, important. Usually, reaction mechanisms are validated to reproduce global parameters like the adiabatic temperature, the global burning rate, the ignition delay time or the laminar flame speed, rarely with an assessment of the ability to reproduce dynamical properties too (Sidhu et al., 1997). In (Acampora et al., 2015) the role of the reaction mechanism in determining the ability of a methaneair mixture to withstand forced perturbations in conditions close to extinction in an adiabatic PSR was investigated. Several issues were highlighted about the ability of global reactions to reproduce the behavior obtained with the well-established GriMech 3.0 (GRI) scheme. In this work, a more sophisticated approach, the parametric continuation (Acampora and Marra, 2015), is adopted to obtain the bifurcation diagrams of a diabatic PSR model with several detailed mechanisms for methane. Results highlights the region of parameters, f.i. the residence time, where discrepancies of results are still significant. It is also illustrated how spontaneous oscillations can arise when a heat loss term is introduced. Simulations in these regions reveal that a very different transient time is obtained before reaching stable oscillations. As a conclusion, it is found that even very detailed mechanisms could be not able to catch the correct dynamics of methane combustion.