| The objective of the present work is the comparison of spray flame oscillations to those of a gaseous flame using the identical combustion chamber and fuel nozzle at the same acoustic boundary conditions. For the experimental study of the flame oscillations a combustion chamber with full optical access was set up, which allows to operate with different fuels either premixed or non-premixed. The thermo acoustic oscillations were detected by microphones located in the combustion chamber and air box, as well as by a photo diode detecting the chemiluminescence of the flame. The study revealed a still undescribed Strouhal related oscillation. Phase-locked LIF measurements were performed in order to visualize the instability. It is shown that the first harmonic is very dominant for the spray flames. This oscillation can be found in gas flames as well but the amplitudes are significantly smaller. For the studied air mass flow rates the frequency ranges from 100 to 280 Hz. The second harmonic of the instability is strongly dominating for perfectly premixed gaseous flames. To separate the influences of atomization, evaporation, air-fuel-mixing, the premixing, equivalence ratio and air preheat temperature are varied. |
