c) Compressor Impeller Creep Life
The creep life of material is a function of stress and temperature. The compressor impeller creep life, therefore, may be roughly estimated from the compressor pressure ratio and suction air temperature. Fig.5 shows the relation between the impeller creep rupture time, suction air temperature, and compressor pressure ratio.
it can be seen that as the engine mounted turbocharger suction air temperature rises, the compressor pressure ratio goes down and so does the impeller creep life. Which means that, for example, the creep life of the compressor impeller in the turbocharger mounted on a supercharged dynamo engine can considerably vary depending on whether the engine is installed and used somewhere in the high latitudes or in the tropics.
The turbocharger suction air temperature, therefore, is a factor of vital importance to the compressor impeller creep life. When predicting the compressor service life, it should be preceded by a careful study on how the turbocharger suction air temperature would change throughout the year.
It should be mentioned in this connection that the cooling air system employed as stated earlier in b) has proved highly effective in extending the compressor impeller service life, i.e., by extending the impeller life time by about 4 as compared with what it was without the cooling with air.
The cooling air system was first employed in 1994 for the compressor impellers of MET53SD and MET66SE turbochargers which were manufactured for use with dynamo engines installed in the low-latitude regions.
