| As a kind of ideal alternative fuel of diesel, biomass fuel can be used in diesel engine. The fuel dilution and soot contamination of engine lubricating oil were not prevented through the gap between cylinder line and piston ring. It is well known that the tribological performance of cylinder line and piston ring is critical to the fuel economy and uselife of engine. In this thesis, the friction and wear behavior of lubricating oil diluted by the biomass fuel or/and contaminated with biomass soot particles were investigated using a cylinder line-piston ring tribomter. The surface morphologies and compositions of tribofilm on worn surfaces were analyzed with the help of the scanning electron microscopy coupled with energy dispersion spectroscopy (SEM/EDS),3D laser scanning microscopy and X-photo-electronic spectroscopy (XPS). To promote the application of biomass fuel in the diesel, it was explored the tribological performance of piston ring and cylinder liner lubricated by the oil effected by the dilution role and soot particles of biomass fuel.(1)Biomass fuel (EBF) used for engine was prepared via the micro-emulsion method. The friction and wear behavior of lubricating oil (T400 CH-4 20W/50) diluted by biomass fuel was evaluated using a piston ring and cylinder line tribometer. The results showed that the biomass fuel reduced the kinematic viscosity and weaken the anti-wear performance of lubricating oil by decreasing the thickness of lubrication oil film. With increasing of biomass fuel content in lubricating oil the friction coefficient increased gradually at 25 ℃. When the biomass fuel content was 6.0 wt%, their wear loss of piston ring and cylinder were maximun. In case of 90 ℃, the friction coefficient increased gradually with the increase of biomass fuel content in lubricating oil. When the biomass fuel content was up to 8.0 wt%, their wear loss of piston ring and cylinder liner were maximun. Both at 25 ℃ and 90 ℃, the wear mechanism of cylinder liner was possible ascribed to the fatigue wear. At the same time, the friction induced the formation of tribofilm including the different contents of ZnO, ironoxides, sulfides, phosphates, nitrogen-containing chemicals. It is well known that the ZnO, FeS, phosphates, nitrogen-containing chemicals were benefit for the anti-friction and anti-wear properties of engine lubricating oil. The wear behaviours of the piston ring and cylinder line were determined by both lubricating oil film and tribofilm.(2) Biomass-fuel soot (BS) was collected with a self-prepared soot trapping equipment. The friction and wear behavior of lubricating oil (T400 CH-4 20W/50) contaminated with different content of soot particles was also conducted on a piston ring and cylinder line tribometer. The results showed thatthe friction coefficient and wear loss decreased with the increase of BS particles content at 25℃. When the diameter sizes of most soot particles were less than the thickness of lubricating oil film, the lubricating oil film can become thicker with the increase of biomass fuel soot content in lubricating oil. SEM results showed that there were furrows and cracks on the cylinder liner. The wear mechanism of cylinder liner was possible ascribed to the fatigue wear and abrasive wear. XPS results showed that the contents of P、S、Zn and N on the cylinder liner surface decreased, and the soot might inhibit the formation of tribofilm as the soot could scratch the cylinder liner surface. The lubricating oil film might play a major role during the rubbing process at 25 ℃. The friction coefficient and mass loss increased with the BS particles content at 90 ℃. Higher Temperatures might cause the oil film thickness thinner. When the diameter size of most soot particles were larger than the thickness of lubricating oil film, the soot particles might act as abrasive and increase the wear. SEM results showed that the furrow and crack became more serious compared with the cases at 25 ℃. The wear mechanism of cylinder liner was also possible ascribed to the fatigue wear and abrasive wear. XPS results showed that the contents and kinds of element were decreased on the cylinder liner surface with increasing the soot contents in lubricating oil. This showed that high temperature could cause the more serious scratching, and the abrasive wear role of soot became more obvious at 90℃.(3) The friction and wear behaviors of lubricating oil (T400 CH-4 20W/50) diluted by biomass fuel and contaminated by soot particles were also conducted on a piston ring and cylinder line tribometer. The results showed thatThe friction coefficient and mass loss increased with increases of the EBF and BS contents at 25 ℃ and 90℃. The friction coefficient and mass loss at 90 ℃ were higher than those at 25 ℃. SEM results showed that the main wear mechanism was a combination of fatigue wear and abrasive wear. XPS results showed that the formation of tribofihn became easy as the biomass fuel might adsorb additives in lubricating oil, but the soot played a negative effect on the formation of tribofilm. The dilution contributed to thinning of the oil film, the soot between rubbing interfaces acted as abrasive which contributed to the lubrication starved.(4) S195 diesel engine was fueled with the biomass fuel for operating about 10 h. The worn surfaces of cylinder line and piston ring were evaluated by a series of modern analysis technologies. The results showed that the main wear mechanism of cylinder surface were fatigue wear, abrasive wear and adhesive wear. There were elements of Fe, C, Si and phorous on the rubbed cylinder surface. It indicated that it was very difficult for the formation of tribofilm on the cylinder surface in an actual diesel engine because of high temperature, high pressure and soot scraping role. The lubricating oil film might play a major role in the tribological performance between piston ring and cylinder liner in case of diesel engine fueled with the biomass fuel. |
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