Combustion monitoring through vibrational data in a turbocharged city car engine

Condition monitoring and optimization of diesel engine has been the focus of a wide research approaches. Techniques have been developed in which in-cylinder pressure measurements are used to calculate peak pressure and burn rates. In the recent past, vibration, acoustic and speed measurements have received considerable attention to this purpose. Methodologies have been developed in which these non-intrusive measurements are employed to estimate the combustion progress. This work is devoted to assess the potential application of a methodology developed by the authors, in which the engine block vibration is used to estimate indicators able to characterize the combustion development. Previous research activity demonstrated that an accelerometer sensor placed in a selected position of the engine block is quite sensitive to the combustion process in a naturally aspirated two-cylinder common rail diesel engine mainly used in micro cars. The objective of this work is to evaluate the applicability of the methodology to a more complex engine architecture (the same engine was downsized by equipping it with a small turbocharger). Measurements were performed in the engine operative field in which the turbocharger is truly effective. The acquired signals were processed in time and frequency domains. Obtained results proved the good accuracy of the estimation of combustion indicators (crank angle corresponding to start of combustion, 50% of mass fraction burnt) via accelerometer signal processing.