| The combustion excitation responses could be extracted from the vibration signal,which is of great theoretical significance and practical value to on-line monitoring,closed-loop control and fault diagnosis for the combustion process of internal combustion engine. In practical application, since the vibration signal contains a large number of noise, the combustion information is submerged in the non-combustion excitation response signal. It is difficult to obtain combustion information directly from the vibration signal owing to the low signal to noise ratio of the combustion excitation response signal.In this paper, the coupling relationship between the non-combustion excitation response signal and the combustion excitation response signal in the vibration signal is analyzed. According to the coupling relationship, the extraction methods of combustion excitation response signal in the vibration velocity signal and the vibration acceleration signal are studied respectively. Methods are proposed to calculate the lag angle between the vibration response signal and the excitation signal. Methods are proposed to describe the high frequency component of the excitation signal based on the parameters related to the combustion process in the vibration signal based on the simulation analysis.The main research work in this paper is as follows:1 Theoretical Analysis of the Relationship between Engine Surface Vibration Signal and Combustion Excitation SignalThe vibration signal contains powerful low-frequency interference that is excited by reciprocating inertial force and other related excitation,which is considered to be excited by reciprocating inertia force through frequency spectrum analysis. Combustion excitation response signal is overlapped by reciprocating inertia response signal in some working conditions, and it is more apparent in vibration velocity signal, which makes it difficult to identify combustion parameters automatically based on measured vibration signals;Vibration system models are built based on Matlab/Simulink, which is used to analyze the effect of cylinder pressure excitation on the lag angle. It can be concluded that the high frequency harmonic component of the combustion excitation signals and lag angle increases with the increment of engine load;Cylinder pressure curves under different working conditions are obtained by changing heat release curve using a one dimensional simulation model of internal combustion engine, which is built by using AVL Boost. Relationship between the energy more than 250Hz and combustion parameters is analyzed. Combustion parameters that characterize the energy that is higher than 250Hz in the cylinder pressure signals are discussed, which lays the foundation. for the indication of proportion of the high frequency components and estimation of the lag angle.2 Extraction and Application of Combustion Excitation Response Signal in Body Surface Vibration Velocity SignalThe measured vibration velocity signal contains powerful low-frequency interference that is excited by reciprocating inertial force and other related excitation.Previously it is treated as a trend item and is removed by using a polynomial fitting method. However, corresponding window and polynomial order needs to be predefined according to this method, which may not be applicable when the working condition changes. The vibration response signals excited by the in-cylinder pressure excitation and the reciprocating inertia force excitation are overlapped in both time and frequency domain. Part of combustion information would be filtered out if the interference is filtered out with a band-stop filter or wavelet decomposition method. The EMD decomposition method can eliminate some non-combustion response signals, but the reconstruction result is very different when choosing different IMFs.A mathematical model is established to describe the response of the reciprocating inertia force excitation. The parameters of the model are recognized with a pattern recognition algorithm, and the response of the reciprocating inertia force excitation is predicted and then the related contributions are removed from the measured vibration velocity signals. The processed results indicate that a fourth-order model and the data of initial compression stroke reach satisfactory results. The impact of the speed fluctuation can be ignored. Meanwhile, the trends of the processed vibration velocity and the cylinder pressure rise rate are similar around the crank angle of the peak pressure, which further supports the method. Feature parameters in the vibration velocity is introduced to characterize the proportion of high frequency components in the vibration velocity signal, which improve the accuracy of combustion parameters based on the vibration velocity signal.3 Extraction of Combustion Excitation Response Signals in Vibration Acceleration SignalsThe measured vibration acceleration signal shows that there also exists reciprocating inertia excitation response in the vibration acceleration signal. The time-frequency analysis method based on Fourier transform is prone to perform false signal when analyzing non-stationary signal. In addition, the processed results depend largely on the selection of the wavelet basis if the low frequency interference is eliminated with the wavelet.As a solution to this issue, EMD is introduced to improve the signal-to-noise ratio of combustion excitation in vibration acceleration signal. EMD is an adaptive signal processing method, and it is very suitable for dealing nonlinear,non-stationary signals. The vibration acceleration signal is decomposed based on EMD to acquire intrinsic mode function (IMF). IMFs highly related to the combustion information are selected to reconstruct the vibration signal. The reconstructed vibration acceleration and the secondary derivative of cylinder pressure shows similar trend.In the reconstructed vibration acceleration, some parameters are used to characterize the high frequency energy, by which the lag angle is estimated. In this way, the location of maximum pressure rise rate and the location of peak pressure is predicted.4 Study on the Applicability of Combustion Excitation Response Signal Extraction MethodOn the SD2100TA two-cylinder diesel engine, the influence on the combustion response excitation of the measuring cylinder from the combustion excitation of the adjacent cylinder was studied. The results show that when the internal combustion engine speed is lower than 7500 r/min,the combustion response signal of adjacent cylinder can't continue to the current cylinder burning. When the engine speed is higher than 7500 r/min, the crank angel corresponding to the time when the combustion response signal of adjacent cylinder is stable will be larger than 180 ?A. But at the end of combustion, the engine system come into the free vibration stage, the frequency of free vibration is higher than 3000Hz, which is higher than the frequency of combustion excitation response signal. Therefore, even if the free vibration caused by the combustion excitation of the adjacent cylinder last to the burning time of the current cylinder, it can be removed by the filtering method.On the 4W34T2 diesel engine, the coupling relationship between the combustion excitation of adjacent cylinder and valve opening, seating and other non-combustion is studied. The combustion excitation response is coupled to the combustion excitation response of the adjacent cylinder, the valve opening, the seating excitation. When the load is low, the influence of the valve excitation is obvious. As the load increases, the energy of the valve excitation response signal decreases gradually in the vibration velocity signal, and the frequency of the response signal of the valve excitation is higher than the combustion excitation response signal. In addition to the combustion information of the current cylinder, the vibration signal of the cylinder head cover also contains partial combustion information of the adjacent cylinder. As a result of the influence of the characteristic of the cylinder pad and the cylinder head cover, the measured vibration signal decreases significantly when the frequency is lower than 1000Hz and higher than 2000Hz, especially in the frequency band lower than 800Hz.On the SD2100TA and GW4D20 diesel engines, methods of identifying the combustion parameters by using the vibration velocity signal and the vibration acceleration signal are verified. In .the tests, the fuel is diesel oil, G30 and G50 respectively. The results show that either the combustion parameters identified from the vibration signal or the cylinder pressure curve can reflect the change of the fuel. The vibration signal obtained from the cylinder head cover contains a relatively significant non-combustion excitation response signal due to the loss of partial combustion information, resulting in the decrease of the recognition accuracy.5 Research on Extracting Combustion Excitation Response of Vibration Acceleration Signal Based on Information Fusion TechnologyModern engine is compact, the effective position may be not inconvenient for installing vibration sensors. A method is proposed to reconstruct the vibration acceleration signal which is closely related to the combustion information based on the information fusion technology and several vibration acceleration signal.The synchronous compression wavelet transform is introduced to obtain high frequency resolution spectrum. The modified Hausdorff distance is used to characterize the similarity of the spectrum of each sensor signal,which is used to obtain the weighting coefficient of each sensor signal.The vibration acceleration signal is reconstructed by using signals measured on different position. The results show that the combustion information contained in the vibration acceleration signal closer to the cylinder is more abundant. The vibration acceleration signal is reconstructed by the sensor signals closer to the cylinder. The reconstructed vibration acceleration signal can be used to identify the combustion parameters. Compared with the vibration acceleration signal measured on the surface of the cylinder head, the reconstructed vibration signal contains less combustion information. |
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