Analysis of excitation source characteristics and their contribution in a 2-cylinder diesel engine

•Maximum amplitudes resulting from Non-combustion excitations and from cylinder pressure are compared.•Characteristics of the main excitations and their responses are analyzed.•Coupling relationships among the main excitations are evaluated.•Contribution level of the reciprocating inertial force and its rule of change are analyzed. Vibration signal of internal combustion engine is excited by the cylinder pressure and other excitations. The response signals caused by different excitations couple together in the time domain and frequency domain, which makes it difficult to extract combustion information from vibration signal. To determine the main excitation sources and the contribution level of the most important excitation that contributes to the vibration in a 2-cylinder diesel engine, the ratios of the maximum value of displacement, velocity and acceleration caused by the non-combustion excitations to those caused by the cylinder pressure are calculated. And a cylinder head-body finite element model of an SD2100TA diesel engine is established to analyze the characteristics of different excitations such as reciprocating inertial force (RIF), piston slap and main bearing load (MBL). According to the analyzed results, the excitations that play a major role on the vibration signal is determined. In addition, the coupling relationship of the excitations is evaluated. The simulation results show that the RIF is the most important excitation in the vibration signal. Finally, the contribution level of the RIF is calculated with the partial coherence function. Results show that the contribution level increases significantly with the increase of the rotation speed and remains basically unchanged with the increase of the torque.