Identification of start of combustion based on contribution level of principal component in vibration signal of cylinder head surface

Abstract

The surface vibration signal measured from diesel engine cylinder head is caused by in-cylinder pressure (ICP) excitation and non-combustion excitations. These excitation response signals are coupled together, which increases the difficulty of identifying combustion information from the vibration signal. Furthermore, there always exists a phase deviation between the identified phase combustion parameter and the theoretical value, which decreases the recognition accuracy of combustion parameter. To accurately extract the combustion information, this paper firstly simulates the vibration signal caused by the combine of ICP, piston side pressure, piston slap and reciprocating inertial force of an SD2100TA diesel engine. Then, the principal component analysis (PCA) is introduced to analyze the contribution level of the combustion excitation response signal in the vibration signal under different working conditions. Meanwhile the influence of measuring point position and number on the contribution level is also discussed. Results show that the contribution level decreases gradually with the increase of the rotation speed and slightly increases with the increase of the torque. In addition, the contribution level is higher when the measuring point is farther away from adjacent cylinder. Finally, the relationship between the contribution level and the identified phase deviation of the start of combustion (SOC) is analyzed, and the deviation correction method is proposed. Results show that the maximum error of SOC after correction is within ± 1 deg.