A nonlinear inverse filtering technique is applied to a four-cylinder diesel engine for diagnosis of power faults inside the cylinders. The technique utilizes cepstral analysis to extract the robust transfer function information and then to predict the cylinder pressure distribution from measured engine vibration signal.
The measured vibration signal is A/D converted with equal sampling time interval and decimated to make up a fixed number of data points per cycle for spectral analysis. Experimental results show that the regenerated pressure signals by cepstral analysis for normal and misfired cylinders agree well with the measured pressure profiles. In addition, comparison of the results using the data with equal time and angle samplings indicates that both methods yield almost identical pressure profiles.
The proposed technique is also tested to check the robustness in practical use by changing the sensor position and the misfired cylinder location.
Finally it is shown that the diagnosis of power faults can also be carried out by low pass filtering of the raw vibration signal.
