ABSTRACT
The basic mechanisms leading to combustion oscillations is in the presence of pressure waves, the flow features large scale motions which drive the instability. The dynamics of the flame is then dominated by processes of hydrodynamic instability, vortex roll-up, vortex interactions, front and reacting stream pulsations, periodic extinctions and resignations, self-acceleration.
Combustion instabilities are a major problem in the design of high performance propulsion systems (rocket motors, jet engine afterburners, ramjets). Instabilities are also observed in power plants and in various industrial processes. They are characterized by large oscillations of the flow parameters, which have many undesirable effects. Low frequency oscillations induce large mechanical vibrations in the system, including the combustion chamber, the feeding lines and the connected rotating machinery. Unstable operation enhances, the heat transfer rates at the combustor walls and in extreme cases this may lead to serious damage and even a total loss of the system.
The present work investigates the changes induced by pilot injections in the acoustic signature of a newly designed 4-slot EV burner using pilot injector at reacting and non-reacting conditions. These changes are affecting the flame stabilization especially in the lean premixed combustion due to the large structures resulting from vortex breakdown and the swirling shear-layers. Pilot injector offered good results in flame stability. The injector position influences the flow field and in turns the flame stability. Different pilot injector fuel shift inside the burner are tested.
All the results are to be compared with those obtained by thepreviously developed 2-slot and 4-slot configuration without pilot injector. This allows the identification of the merits and/or drawbacks of both designs.