High Speed Visualization of Flame Response in a LOX/H2 Combustion Chamber during external Excitation

Kurzfassung

With a model combustion chamber the interaction of an acoustic excitation with a burning LOX/H2 spray was investigated. Pressure oscillations are coupled into the combustion chamber by an additional exhaust nozzle and a siren wheel. Due to the fact that the orientation of the excited acoustic modes can be fixed with this secondary nozzle it is possible to investigate the interaction of acoustics with combustion chamber processes like injection, atomization, vaporization, mixture formation and combustion either with the spray in a pressure node or anti node. Thus the role of pressure or velocity coupling with the processes mentioned above can be studied. For a variety of injection conditions the interaction of the acoustic excitation with the spray flame has been investigated. Only damped acoustic oscillations have been observed, at no operating conditions combustion instabilities were found. High speed visualization of the OH emission of the flame is used to get information on the spatially and temporally resolved evolution of the heat release. From the OH-emission and dynamic pressure recordings a response factor of the combustion process is determined for the case of the excitation of the first tangential mode (1T). The acoustic 1T-resonances of the combustor show non-Lorentzian line profiles. There is indication that the excited modes are not pure but that there is always a superposition of various different eigenmodes in the combustion chamber. This complex dynamics of the acoustic field is not well understood up to now.