4.1. Influence of lubricating oil temperature on the compressor performance
As already discussed, the lubricating oil temperature appears to have a strong impact on the turbocharger performance. Mechanical power losses depend on oil viscosity, which is directly linked to oil temperature. Furthermore, heat exchange increases for high oil temperature and low rotational speeds.
Experiments show little difference in mechanical power given to the compressor shaft by the turbine, except for low rotational speeds (Fig. 4a). In Fig. 4b, it can be clearly seen that when the oil temperature is increased, the mechanical power provided by the torquemeter drops, with a difference of about 40% between the two extreme situations (20 °C and 80 °C). Although this difference between the two situations persists, when the speed increases the difference narrows and at 110,000 rpm it can be neglected.