Investigation Into Tribological Behaviour Of Engine Piston Ring-cylinder Liner Based On Acoustic Emission Technologies And Wavelet Analysis

Piston ring and cylinder liner is the most important parts of an internal combustion engine, as the power performance, fuel economy and emission characteristics of the engine are heavily dependent upon the performance of the tribological behavior of these parts. This means that the on-line diagnosis and monitoring of their frictional and lubricating state have great practical significances for reducing fuel consumption, improving energy efficiency and increasing the working lifespan of internal combustion engines. Unfortunately, less experimental works have been found in direction due to critical challenges of complication of their tribological behaviour and difficulties of direct measurements. AE(Acoustic emission) technique is an advanced NDT(non-destructive testing) technology, has widely used for the assessment of structure integrity, the component examination of fatigue and cracks, the test of friction lubrication between different materials, etc. Many domestic and international scholars has studied actively the friction and lubrication of piston ring and cylinder liner system through the AE technique in recent years, but there has no an effective test method for measuring and analyzing the behavior of piston ring and cylinder liner, implementation to evaluated engine lubrication state during engine running environment.In this investigation, a symmetric experimental study was carried out based on a 1110 II type single cylinder diesel engine, AE signals were obtained on the engine body under different loads and speeds. In particular, it has obtained AE responses under the multi-phase lubrication conditions in which the lubricant was mixed with different degrees of nanoparticles. Because there have many exciting source at the engine surface, to extract lubrication related AE contents, a number of conventional denoise methods have been studied for suppressing the influences of combustions and valve. This leads to a novel adaptive threshold scheme that reduces the influences through maximizing the AE content in the middle engine strokes where lubrication AE is more significant due to the effect of piston velocity. In the same time, it is also suggested to use the average envelop amplitude to indicate the friction effect.The results show that using wavelet multi-resolution analysis and hard threshold de-noising method can effectively restrain the influence of the large amplitude as combustions and valve, obtain the AE signal at the central of piston stroke caused by the friction AE events can make clear differences between different lube oil characteristics. In particular, they exhibit lower amplitudes for the case when more nanoparticles are in the base lubricant. This show the effect of nanoparticles may acts as effective lubricant in reducing engine friction. Friction caused by acoustic emission signal increases obviously with the increase of engine speed, at the low speed, the average of AE decreased with the increase of load, while at the high speed, load has little effect on the mean of the AE signal. The results of using an improved adaptive threshold selection wavelet thresholding method under piston velocity profile constraint have an obvious advantage over traditional hard threshold noise reduction method. Is obtained by eigenvalue analysis, the optimal threshold and the average of AE in the middle of the engine stroke can effectively characterize the lubrication state of piston ring-liner system.