Friction Lubrication State Identification And Fault Monitoring Of Internal Combustion Engine Based On Acoustic Emission(AE) Technology

Diesel engine is one of the most commonly used power machinery,it is widely used in automobiles,ships,agricultural machinery and other fields.The cylinder liner-piston ring is one of the most important internal friction pairs in diesel engines.Its friction lubrication status affects the engine's efficiency and longevity directly,and good lubrication can reduce the friction between cylinder liner and piston ring,reduce power loss,and effectively prevent equipment failure.However,due to the complexity of cylinder-piston ring work environment,it is often difficult to achieve on-line inspection.In order to improve the performance and reliability of the engine,Based on acoustic emission(Acoustic emission,AE)detection technology,this article studies the tribological behavior of the piston ring and cylinder liner in the unit work cycle.This method has low requirements on the test environment,it has high sensitivity,rapid diagnosis,and can achieve lubrication status.Non-invasive online non-intrusive detection.In order to better correlate the acoustic emission signal with the lubrication state,the asperity-asperity collision(AAC)model and the fluid-asperity interaction(FAI)model were established,the AAC effects are more concentrated in near the TDC and BDC,the FAI effect is more concentrated in the middle of the stroke,which provides a solid theoretical basis for the analysis of acousticemission signals through the establishment of the mechanism model,and also provides the possibility of on-line monitoring the lubrication state.In this paper,a QCH1125 single-cylinder diesel engine of a company is tested on working conditions,AE signals is obtained on the surface of the cylinder under different speeds,loads,and viscosities.The wavelet denoise method was used to remove the fixed-angle noise signal,and the wavelet decomposition was used to determine the optimal number of wavelet decomposition layers.According to the correlation between speed and acoustic emission signal,an adaptive threshold-based noise reduction method was proposed to achieve the reconstruction of the acoustic emission signal in the middle of the stroke,and envelope processing of the reconstructed signal,The root mean square(RMS)value is taken as a parameter for characterizing the lubrication state.The results show that the AE signal produced by the FAI effect is mainly concentrated in the middle of the piston stroke.Because the oil film thickness and the piston velocity are the largest in the middle of the stroke,the effect of FAI effects is more obvious,The RMS value of the AE signal amplitude is positively related to the rotational speed and the viscosity of the lubricant,but the effect of the load on the FAI is not significant,which is consistent with the established model.At the same time,the correctness of the self-adaptive threshold denoising method based on the piston speed curve is also proved.In order to verify the effectiveness of the proposed monitoring method,two types of typical lubrication fault test and analysis were carried out based on the internal combustion engine bench.In the case of poor lubrication,the reduction of oil volume makes the hydrodynamic lubrication effect in the middle of the stroke weaker and reduces the thickness of the formed oil film,resulting in a reduction in the FAI effect.However,the amplitude of the AE signal generated by the AAC is increased significantly.The friction between the particulatematter and the asperity was enhanced in the oil,which proved that the lubrication began to be abnormal.When the lubricant oil contains water,the FAI effect is weakened due to the change of the viscosity of the lubricant,while the AAC effect does not change much,that's because the viscosity does not affect the impact function of the AAC.The friction-lubricated condition identification method for internal combustion engines based on the analysis of acoustic emission signals proposed in this paper can effectively identify complex lubrication faults,a new non-destructive on-line detection method is provided for the friction lubrication status monitoring of the cylinder liner-piston ring.