How long do engines last? (BAM-Press Release No 20/2018)
The maintenance intervals for exhaust gas turbochargers, which are frequently used in internal combustion engines, are dictated by various factors including the aluminium radial compressor wheels. The problem is that the temperature rises as the air is compressed, causing the material to age and lose its original strength. It has not been possible until now to describe this ageing process and therefore to predict the service life of the component with sufficient accuracy.
Having been involved in a cooperation project with the Fraunhofer Institute for Mechanics of Materials (IWM), the BAM and the IWM have succeeded in developing a computational model which provides a more precise description.
Exhaust gas turbochargers are used in many internal combustion engines in order to utilise the energy of the exhaust gases, at least to some extent. In a car which is driven only a few kilometres a day, the component is under load only for short intervals. The situation is different when the engine is in constant use for many hours, as might be the case on a fishing trawler used in deep-sea fishing, for example. It is therefore good to know how long the component is likely to last in order to plan the maintenance intervals accordingly.
With this objective in mind, research scientists at the BAM have taken a closer look at the material, an aluminium alloy. The material is cured in the manufacturing process at 195 degrees Celsiusto attain its optimum strength. When the air is compressed, the temperature increases and the material ages. “In order to learn more about the ageing process, we investigated how the microstructure and the strength of the aluminium alloy changes over a period of almost three years if the temperatures are at 190 degrees Celsius or just below,” explained Prof. Dr.-Ing. Birgit Skrotzki, Head of the Division of Experimental and Model Based Mechanical Behaviour of Materials. The data obtained on the microstructure are taken as a basis for an extended computational model which also considers the loss of material strength. It was possible as a result to improve existing models on ageing, deformation and service life.
“The computational model therefore helps us to be more accurate at predicting the service life of aluminium radial compressor wheels, even when they are subject to heavy operational demands,” added Skrotzki, summarising the advantage which will allow manufacturers and users to calculate how long the engine will run reliably – whether in city traffic or at sea.
Venio Quinque, M.A., LL.M./LL.B.
Head of Section Corporate Communications
Bundesanstalt für Materialforschung und –prüfung (BAM)
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