Efficient On-Board Pegging Calculation from Piezo-Electric Sensor Signal for Real Time In-Cylinder Pressure Offset Compensation

The introduction of piezo-electric sensor on mass produced engines for in-cylinder pressure measurement represents a near future step in order to improve combustion control. Piezo-electric sensors provide pressure measurements affected by offset error and drift due to thermal sensitivity: a pressure reference is needed for each cycle in order to obtain the actual pressure value (pegging). Three methods for the evaluation of the offset, based on the hypothesis of polytropic compression, have been analyzed in this work: (1) a three-point referencing method, (2) a linear least-square method and (3) a non-linear least-square method. From such a comparison the three-point referencing method appeared the best suited for on-board calculation since it has the lowest computational cost even if it suffers from noise sensitivity. Hence, the accuracy and the efficiency of this method have been improved by means of an original methodology. The proposed method has been applied both to simulated and to experimental signals gathered from a 4-stroke spark-ignited engine. The results are compared to those obtained by using the other two methods showing much better accuracy in all the examined tests. Finally, a computational cost analysis proves the feasibility of the proposed method for efficient on-board pegging calculation with modern engine control units.