Project Leader:	Professor Dr-Ing Horst Rulfs
Research Assistant:	Dipl-Ing M Wöhnke
Duration:	01.01.1993 - 28.02.1996

 

The development of medium speed diesel engines with improved fuel efficiencies and reduced pollutant emissions will be influenced to a large extent by the quality of the fuel injection systems available. Future requirements call for optimised injection systems with very high injection pressures of over 1,500 bar. Due to feedback effects at the low pressure side, pressure hammers up to approximately 100 bar and cavitation (nucleation) occur in the regulating rod of the cylinder of the injection pump. The colliding cavitation bubbles (implosion) cause impulsive pressure fluctuations which, with the already present there powerful fluid stream, cause significant surface material losses.

These cavitation damages are known in the praxis since a long time. Nevertheless it is still frequently reported that pistons and cylinders of injection pumps must be replaced after only 10,000 operating hours.

Aim of this research project was to investigate these complex cavitation phenomena in the regulating rod and study the influence on it of operational and constructive parameters. In addition, the onset of cavitation was studied optically in combination with pressure sensor monitoring.

To make possible optical monitoring it was necessary to build a test rig with a large injection pump (piston diameter 47 mm). The monitoring of the cavitation phenomena was done through saphire windows and observations were taken from three different directions. With an external short time lighting source (10 ms) it was possible to take high-speed video sequences which were digitalised and then recorded.

For the first time it was possible to video monitor these complex cavitation phenomena and develop new ideas for explaining the many cavitation failures occurring in practice. Tests with altered pump elements have shown the potential and limitations of constructive and operational improvement interventions in reducing the phenomenon.