vibration analysis to estimate turbocharger speed fluctuation in diesel engines

Abstract The optimum management of the engine system has a crucial role in order to achieve high efficiency and reduced pollutant emissions. Advanced methods have been proposed, in which several types of sensors are used to directly/indirectly sense the combustion and to provide a feedback signal to optimize the engine management. In turbocharged engines, it has been demonstrated that a relationship exists between the rotational speed of the turbocharger and the thermo-fluid dynamic condition of the gases at the exhaust valve opening. Such a relation allows to establish a link between the engine operating conditions in terms of speed, load and injection settings and the turbocharger speed. A research activity was performed aimed at developing a methodology in which the signal from an accelerometer mounted on the compressor housing was used to extract information about the turbocharger speed value. The activity was organized in two subsequent steps, each one focused on one specific objective: – estimation of the mean turbocharger rotational speed – evaluation of the turbocharger speed fluctuations. Tests were performed on a small displacement two-cylinder diesel engine mainly used in urban vehicles that was equipped with a turbocharger. The results obtained during the first step of activity demonstrated the opportunity of further investigations in order to compute the turbocharger speed fluctuation from the accelerometer signal processing. This paper is devoted to present the results of the second step of the research activity, with the final aim of realizing a non intrusive control of combustion process, in which the variation of combustion development as regards nominal condition is detected via the estimation of the turbocharger speed.