Combustion dynamics in a diabatic PSR with global, reduced and 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. Reduced chemical schemes are required for CFD simulations of reactive industrial flows. Usually, the reduction of the reaction mechanism is performed ensuring that the reduced scheme reproduces global parameters like the adiabatic temperature, the global burning rate or the laminar flame speed, rarely with an assessment of the ability to reproduce dynamical properties too [1,2]. In [3], the role of the reaction mechanism in determining the ability of a methane-air 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 [4]. In this work a diabatic PSR model is assumed. The previous study is extended to include a characterization of spontaneous oscillations, that can arise when a heat loss term is introduced. The bifurcation diagrams with the different mechanisms are preliminary determined. Then, simulations are performed in key solution points where periodic solutions establish, spontaneously or by a forcing. Comparison of results allows to highlight several features of system dynamic response and their dependences upon the selected mechanism.