抄録
In this contribution, an initial investigation of the ignition behavior of large two-stroke marine diesel sprays has been performed. At engine-like conditions, the OH radical was traced with an intensified high speed camera and a sophisticated optical setup. A series of spectroscopic measurements showed, however, that the soot incandescence strongly contributes to the UV signal, superimposing with or even masking the chemiluminescence of the OH radical. As the combustion of typical fuels used in large two-stroke engines involves the formation of non-negligible amounts of soot, the signal is almost omnipresent during the oxidation process. A differentiation between the UV-light emitted by the OH radical and the UV-light emitted by soot incandescence is only possible when both signals are measured separately. Therefore, a second high speed camera recorded the light coming from soot incandescence. In addition, it recorded the background illuminated spray plume to make an exact positioning of the OH* signal relative to the spray possible. A comparison of the two images then allowed the differentiation between the two light sources. In a first measurement series, which included a temperature variation, ignition delay, ignition location and flame lift-off have been measured. The results are in accordance with literature, as they show a dramatic decrease in ignition delay towards higher gas temperature. On the other hand the standard deviation increases towards lower gas temperatures. The ignition location and lift-off showed similar behavior: Lower gas temperature corresponds to an increase of the distance between ignition location/lift-off and nozzle orifice along with increased standard deviation. It could be shown that the applied technique works for the investigation of large marine diesel engine combustion systems.
