1. Introduction
Nowadays, the tendency to reduce the cylinder capacity – downsizing – in reciprocating internal combustion (IC) engines requires the use of turbochargers. The final objective of this boost is to maintain or increase the engine air mass flow, thereby increasing engine power. The performance and reliability of these turbochargers are related with many factors like mechanical losses, heat transfer, shaft motion, lubrication, etc.
The dynamic model of the shaft has been studied extensively since the early twentieth century until nowadays [1], [2], [3] and [4]. The focus of these models has changed with technological developments, from the purely theoretical until their validation by experimental techniques. These types of models have been used to study the operative problems of turbomachinery [5]. Nowadays, some experimental measurement techniques with accelerometers [6] and laser [7], feedback these models, and both models and experimental techniques contribute to improve the knowledge about the functioning of these shafts.
The lubrication problems in these turbochargers have been extensively studied both experimentally, by measuring the thermodynamic variables in turbocharger test benches [8], and theoretical, by means of CFD models [9] and [10]. In this paper the whirl movement of the shaft of an IC engine turbocharger is measured by digital processing of high magnification images of the rotor axis during normal and abnormal operation. The objective is to obtain information about the whirl shaft movement previous to and during turbocharger lubrication failure tests. This information goes from the movement of the shaft to another type of visual information, as the apparition of oil on the compressor side, or the deformation of the shaft tip. Furthermore, this technique is not intrusive and robust enough to avoid the destruction of the measurement components if a catastrophic failure of the turbocharger happens. To accomplish these objectives, a window in the compressor inlet duct with a camera focused on the shaft tip has been used [11]. To obtain the expected results some difficulties presented by the test bench Diesel engines used in turbocharging [12] and [13] should be considered such as structural vibration and space to install the equipment. During these tests, turbocharger thermodynamic variables have been also recorded to obtain complete information on the evolution of the turbocharger when it has lubrication problems [14].
This paper describes the test bench configuration and the different image processing techniques to obtain information about the shaft motion.