Vibration based diagnostics of combustion process in diesel engines

The main objective of this paper is to obtain combustion parameters, which can be use for engine diagnostics proposes. The main combustion parameters are the maximum cylinder pressure (p(max,)) and the derivative of the pressure rise (dp/d alpha). The based idea is to perform the reconstruction of the cylinder pressure by using the engine Transfer Function (TF) and the measured vibration response signal of the engine surface. The analysis is based on a non-linear method called real cepstrum and signal processing techniques, The TFs were adapted to slightly different situations such as other cylinders of the same engine, in particular where use can be made of symmetry. A matrix with engine TFs for varying speed and load was obtained this can be used as a data bank of TFs for reconstruction of the cylinder pressure at different operating conditions. An extensive analysis of the cycle to cycle variations was carried out for both the measured and reconstructed cylinder pressure.