Abstract
Wear has recently been observed on the injection equipment of diesel engines and also on petrol engines with fuel injection, the causes of which are to be sought in the formation of cavities in the liquid and their collapse. The prerequisites for cavitation and subsequent aggressive implosion exist, apart from the places behind throttling points where the flow is subject to a high drop in pressure, also in those pressure pipes where underpressure waves of a high amplitude occur as a result of reflection or a sudden pressure relief.
The wear occurring in such cases is at the same time influenced by various factors which it has been possible to determine only qualitatively, such as the surface quality of the pipe walls, mechanical stresses in the material, physical properties of the liquid, etc., and may lead to functional disturbances on the nozzle and a quick bursting of the pipe.
As an example of this, the effect of cavitation aggression on a high-speed four-stroke rail-traction engine having an output per cylinder of 90 hp at 1500 rev/min is shown. It is further explained how conclusions can be drawn concerning the existence of cavitation by means of pressure diagrams, the places in the pipe system that are particularly endangered, and how this can be adequately remedied by changes in the hydraulic system.
A further example of cavitation attack by pressure waves is the heavily worn injection pipe of a high-pressure turbocharged four-stroke marine diesel engine with an output per cylinder of 550 hp at a speed of 400 rev/min. Here, the inner wall of the pipe was also destroyed quickly and, as a result, particles of material were able to get to the nozzle.
Reducing the pressure relief in the pressure pipe at the end of injection remedied the situation, without any after-drip being observed.
Finally, the paper discusses an attack on the injection pump plunger as an example of flow cavitation.
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