Fig. 1 Schematic diagram of experimental apparatus
At a relatively low temperature (400 〜 420 K), this H2SO4 precipitate is formed around soot particles serving as nuclei and adheres to engine components such as the cylinder liner, piston, piston ring and so on, thereby eroding their surfaces(erosion wear). The resultant rough, eroded surfaces are rubbed against abrasive powder, oxide compound of lubricating oil, and soot in operation, producing further wear(abrasion wear) (6) .
In the present study, no attempt is made to identify causes of increased wear amounts. Instead, to understand an intrinsic nature of EGR, the effects of the soot and SOx emissions in recirculated exhaust gas on the wear of cylinder liner, piston and piston rings were experimentally investigated on a diesel engine with EGR application. And the findings may be utilized as preliminary data for designing and developing a feasible control device of the practical EGR system in diesel engines.
2. EXPERIMENTAL APPARATUS AND TECHNIQUES
2.1 Experimental Apparatus
The schematic diagram of experimental apparatus is shown in Fig. 1. The test engine eraployed in the present study was a four cycle, two-cylinder, water-cooled, indirect injection, marine diesel engine manufactured in Korea. The major specifications of the engine are presented in Table 1.
To investigate the effects of recirculated exhaust gas on the wear of cylinder liner, piston and piston rings, No. 1 cylinder of the two cylinders was fed with air passed through the surge tank. While No. 2 cylinder was fed with the intake mixture of fresh air and recirculated exhaust gas of a 20% EGR rate. The exhaust gas was passed through a novel diesel soot-removal device with a cylinder-type scrubber and entered into the surge tank to minimize the surging.
The cross-section of a novel diesel soot-removal system with a cylinder-type scrubber that was designed and manufactured to eliminate soot contents from the recirculated exhaust gas is presented in Fig. 2. The exhaust gas emitted from the diesel engine is directed into the inlet port in the lower side of the scrubber and then passes through the disturbed rings before the soot is removed by water sprayed from 144 nozzle holes of 1 mm in diameter. The amount of sprayed water is automatically controlled by a flow meter with a solenoid valve according to EGR rate. In this study, however, the amount was constantly fixed since only a 20% EGR rate was applied. The resultant soot-removed exhaust gas is passed through the demister for dehydration and is flowed into the surge tank through outlet port, where it is mixed with the incoming fresh air.
A discharging port was installed in the lower part of the scrubber in order to prevent the sprayed water from flowing over the inlet. And also a baffle plate was installed on the floor of the scrubber to keep the incoming exhaust air from escaping directly into the discharging port.
The performance of the water injection device used in this study has been mentioned in previous work (5); that soot-removal efficiency without EGR application was approximately 30〜50%, though it was variable depending on engine load levels.
