Early stages of methane combustion in an atmospheric cylindrical chamber with on-axis or off-axis shear co-axial injector

Using Computational Fluid Dynamics (CFD), the early stages of methane combustion in an atmospheric cylindrical chamber were studied for both on-axis and off-axis swirl injector. The goal of these computations was to shed some light on the early development of combustion instability by analyzing the dynamic pressure field in the chamber after the onset of combustion. The CFD code used was Loci-CHEM and the initial conditions in the chamber, as well as the injector geometry and parameters, were obtained from earlier experiments. The combustion kinetics of atmospheric methane-oxygen burning were simulated using a one-step overall reaction with all the kinetic parameters obtained from literature. The unsteady nature of the combustion phenomena and the diverse time and length scales make these computations intensive. In order to reduce computational cost, the hybrid RANS/LES modeling approach was used. For the on-axis injector case, two computations were carried out; one using the axi-symmetric assumption and the other was fully three dimensional. The pressure wave generated by the ignition and the subsequent combustion was in both cases symmetric and propagated outwardly towards the chamber wall. This pressure field is indicative of the presence of a radial mode which was observed in the experiments. For the off-axis injector, only one three dimensional computation was carried out and in this case, the pressure field was asymmetrical with a tangential component visible due to the proximity of the chamber wall. This is also in agreement with the experimental observations.