Shiozaki et al.(6) have conducted an experiment on the wear of piston rings along with cylinder liner. They have found that factors the affecting ring wear were very complicated, and were much more complicated in case of EGR application. They have also reported that the wear was drastically greater with increasing engine load as well as EGR application, while the effect of engine speed was not clear. As compared with the wear rate without EGR, the wear rate of the sliding surface in top ring was four to five times greater in case of 20% EGR rate application. The sliding surface also showed four times greater wear rate, and wear rates of the top and bottom surfaces was 1.5 times in No. 2 ring.
Ca(OH)2 contained in lubricating oil acts as a neutralizing agent to inhibit erosion. Because recirculated exhaust gases with EGR application cause the quick drop of alkali index in lubricating oil and the speedy increase of the insoluble component in normal heptane and resin component, EGR application in a diesel engine may lead to serious deterioration of lubricating oil. Increased soot emissions due to greater EGR rate is mixed with lubricating oil to add to the insoluble component in normal heptane; the eroded surfaces of cylinder liner, piston and piston rings are rubbed with the oxide compound of lubricating oil and soot emissions as an abrasive, resulting in further wear in rings and liner. The lubricating oil mixed with this abrasive powder can add to deterioration, resulting in the increase of the insoluble component in normal heptane and resin component. It can be suggested that the reason for the different wear amounts of piston rings in this study may have been that the lubricating oil did not act properly as a neutralizing agent because H2SO4 concentration showed quite significant differences on parts of the rings; rings with higher H2SO4 concentration couldn't be sufficiently protected by the lubricating oil.(15〜24)
4. CONCLUSION
The EGR application in diesel engines poses many problems such as exhaust emissions, fuel economy, durability and so on. However, EGR may be recommended as one of the most effective methods for reducing NOx emissions because there are few strategies to effectively reduce them. Therefore, many research efforts are necessary to minimize the problems of EGR application. In the present study, a two-cylinder diesel engine was operated with fresh air fed into one cylinder and recirculated 20% exhaust gas into the other cylinder to investigate the effect of recirculated exhaust gas on the wear of cylinder liner, piston and piston rings. The major results are as follows:
1) The mean wear rate of cylinder liner was approximately constant regardless of measuring positions in case of no EGR application, while the mean wear rate with EGR was greater in the second half than the first half.
2) The mean wear rate of piston skirt part with EGR application was slightly higher than that without EGR. The piston diameter of head part due to soot adhesion and erosion wear increased, particularly more remarkable in case of EGR application.
3) With regard to piston rings, the mean thickness wear rate of all rings was greater than that of top ring in case of no EGR. The mean width wear rate in top ring was significantly higher, particularly much greater in case of EGR. The mean thickness wear rate of oil rings with no EGR was higher than that with EGR, while the mean width wear rate was higher with EGR application.
The present study represented wear rate as length differences measured before and after the experiment. In further studies, however, it may be hoped that though it may not be simple, attempts will be made to measure wear rate as mass differences. In addition, supplementary researches such as analyzing photographs of erosion and wear defect parts, and measuring the soot contents and H2SO4 component contained in lubricating oil are also needed.
ACKNOWLEDGEMENTS
This work was partly supported by a 1995 Special Fund for University Research Institute of Korea Research Foundation, an Industry- University Consortium Special Fund of the Small and Medium Business Administration, and Sam Jeon Construction Co., Ltd. hosted by Research Institute of Industrial Technology of Gyeongsang National University, and the Brain Korea 21 Project. We would like to thank Professor T. Kamimoto(Emeritus Professor of TIT) of Tokai University for his valuable discussion and encouragement during the course of this study.
REFERENCES
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2. Arcoumanis, C., Bae, C., Nagwaney, A., and White law, J. H., "Effect of EGR on Combustion Development in a 1.9L DI Diesel Optical Engine," SAE 950850(1995), pp. 169〜193.
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