No abstract

No abstract

No abstract

This study reports novel measurements on the effects of pressure on the lift-off behavior and the stabilization mechanism of turbulent non-premixed methane jet flames. A high-pressure combustion duct (HPCD) was operated within the range of pressure P = to 7 bar using jet velocities of 4 m.s-1  Uj  30 m.s-1 and co-flow velocities of 0.23 m.s-1  Uc  0.60 m.s-1. Lift-off heights were measured from chemiluminescence pictures while joint images of hydroxyl and velocity, performed using joint PLIF-OH/PIV, were used to extract information about the stabilization mechanism. It is shown that while the lift-off height generally increases with pressure, the impact of pressure depends on the magnitude of the co-flow velocity. For Uc = 0.30 m.s-1 , the flame's base remains near the nozzle over the entire pressure range and the measured flame speeds indicate that edge-flame stabilization is dominant. The slope of the lift-off height vs jet velocity curves is positive. For Uc = 0.60 m.s-1 and P > 2 bar, the flame stabilizes further downstream and a transition to turbulent premixed flame propagation appears to have occurred. At these conditions, the slope of the lift-off height vs jet velocity curves becomes negative. This reversal at high pressure is a new result for methane. More importantly, the transition in the stabilization mechanism with increasing Uc is consistent with results reported earlier for ethylene and appears to be independent of the fuel.

This paper focuses on the experimental and numerical investigation of the shape taken by confined turbulent CH 4 /H 2 /air premixed flames stabilized over a bluff-body swirling injector. Two configurations, which correspond to two levels of H 2 enrichment in the CH 4 /H 2 fuel blend, are investigated. Experiments show that high H 2 concentrations promote M flame shapes, whereas V flame shapes are observed for lower values of H 2 enrichment. In both cases, non-reacting and reacting flow Large Eddy Simulation (LES) calculations were performed. Numerical results are compared with detailed velocimetry measurements under non-reacting and reacting conditions, OH-laser induced fluorescence and OH * chemiluminescence measurements. All temperatures of solid walls of the experimental setup including the combustor dump plane, the injector central rod tip, the combustor sidewalls and the quartz windows were also characterized. Assuming a fully adiabatic combustion chamber, LES always predicts an M flame shape and does not capture the V to M shape transition observed in the experiments when the hydrogen concentration in the fuel blend is increased. By accounting for non-adiabaticity using measured thermal boundary conditions, simulations predict the correct flame stabilization for both V and M flames and show a good agreement with experiments in terms of flame shape. Key features that need to be included in non-adiabatic simulations are finally stressed out.

No abstract

No abstract

No abstract