Abstract
Injection systems of modern diesel engines are the key to increase the fuel efficiency and to lower pollutant emissions. Therefore, a detailed understanding of the spray generated by the injector nozzle is crucial to optimize the process of the mixture formation and thus the combustion process. Up to now, the spray behavior in the near nozzle field is not completely understood. Standard optical diagnostic methods are known to fail visualizing the near nozzle region due to the high optical density of the diesel spray. One approach to address this challenge is the optical connectivity method, described by Charalampous et al.. It can be used to measure the length of the continuous liquid jet core in sprays. Here, the laser light is directed through the injection nozzle to illuminate the liquid jet internally. The spray breakup interrupts a further light transfer and thus limits the illuminated area to the liquid core. While so far a specially designed injector was necessary, in this work a new approach is invented where the laser light is guided by an optical fiber into the sack hole through one of the injector holes of an unmodified stock injector. The feasibility of this approach is demonstrated on a heavy duty diesel injector with fuel pressures up to 80 MPa, being adapted to the large high pressure injection chamber of the Institute of Technical Combustion in Hannover. Other than in, no additional tracer fuel was necessary, as the direct stray light yielded enough signal intensity. First results of the transient behavior of the liquid core length are discussed.
