Ignition behavior of marine diesel sprays. Investigation of marine diesel ignition and combustion at engine-like conditions by means of OH* chemiluminescence and soot incandescence

Abstract

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 sophisti-cated optical setup. A series of spectroscopic measurements showed, however, that the soot incandescence strongly con-tributes to the UV signal, superimposing with or even masking the chemiluminescence of the OH radical. As the com-bustion 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.