Optimization of the Impulsiveness Performance of a Diesel Engine 2011-01-1668

The interior sound quality of passenger cars has a big impact on the perceived comfort of the vehicle. With today's direct-injection diesel engines this fact gains importance, since the customers are more and more attracted by them due to their low fuel consumption and their good driving performance. In the course of the development of diesel technology, the typical impulsive noise of diesel combustion engines (the so-called “diesel knocking”) is less and less tolerated. Furthermore, the possibilities to tune the combustion with respect to noise are nowadays more limited due to the more stringent targets for CO2 and Euro 5/6 emissions. This possibly leads to a higher risk in not fulfilling exterior and interior sound quality targets like diesel knocking noise.

The diesel knocking perceived inside the vehicle is influenced by various parameters. In addition to the combustion process itself, the transfer characteristics of the engine block, the engine mounting system and the various secondary transfer paths of the vehicle have a major influence on the perceived diesel sound quality. In addition, the intensity of the diesel knocking also differs significantly, depending on the engine speed and the engine load. This fact complicates the analysis and objective assessment of the diesel knocking significantly.

The scope of this paper is the application of time-domain based transfer path analysis in combination with newly developed objective parameters to describe the phenomenon of diesel knocking. The test methods, the parameters used and the analysis methods are exemplified. As a result of the investigation the main airborne and structure-borne transfer paths for diesel knocking are identified and possible countermeasures to improve the sound quality are predicted by simulation. Finally, the predicted improvement of the perceived sound quality is validated in the vehicle.