Fig. 3 Measurement spots of cylinder liner, piston and piston ring
Thus this device may be recommended as a method for soot removal in diesel engines with EGR system.
2.2 Experimental Techniques
The engine was operated for 400 hours at an engine load of 75% and an engine speed of 1600 rpm, with or without EGR, in order to measure the wear rates of cylinder liner, piston and piston rings as affected by the two conditions. Though the engine load, speed and EGR rate were fixed throughout the experimental period, the following variations were observed during the 400 hour engine operation: ± 5% for engine load; ± 1% for engine speed; and ± 10% for EGR rate.
A water-cooling heat exchanger was employed to keep the temperature of lubricating oil between 333〜343 K. K type thermocouples as temperature sensor were installed into the inlet and outlet of cooling water to control the temperature between 313〜323 K, and then to check regularly the engine operation and combustion. Another K type thermocouple was installed in the exhaust pipe to measure exhaust gas temperature; 553〜573 K was the adequate operating range. Fuel injection time was fixed at 15.3°BTDC. In general, the EGR rate is calculated by measuring the CO2 concentrations at intake and exhaust manifolds (4) but the present study calculated the EGR rate as the ratio of exhaust gas amount recirculated through EGR valve to total intake mixture amount.
In order to measure the wear amount of cylinder liner inner diameter after the experiment, the engine was disassembled prior to it. The inner diameter of cylinder liner was measured at intervals of 90°rotated positions with distances of 30, 60, 90 and 110 mm from the top; A bore gauge was used for these measurements. The measurement positions are shown in Fig. 3 (a). This gauge has a measurement range of 50〜100 mm and a minimum scale of 1 μm. For the outer diameter of piston, a digital micrometer was used to take measurements of the head part 10 mm away from the piston crown and the skirt part 100 mm away from the piston crown, as shown in Fig. 3 (b). The micrometer has a measurement range of 75〜100 mm, with a minimum scale of 1 μm. To distinguish the right-left and front-rear of measurement spots, the position located in piston pin hole was defined as a front spot for the measurements. The right spot was decided as the point 90° rotated counterclockwise from the front. For piston rings, the width and thickness of the compression rings from the top to No. 3 and the oil rings from No. 1 to No. 2 were measured by the digital micrometer at three spots with intervals of 120° beginning from the ring end gap shown in Fig. 3 (C).
3. RESULTS AND DISCUSSION
3.1 Wear Rate of Cylinder Liners
The inner diameters of the cylinder liners were measured on No. 1 (with fresh air only) and No. 2 (with an EGR rate of 20%) cylinders as mentioned above. Fig. 4 shows the measured values of the inner diameters obtained at a right-left spot with and without EGR before and after experiments, and a comparison between the wear rates of measured spots. As compared with measurements before experiments, the cylinder liners were found to have increased wear amounts regardless of EGR application; with higher wear amounts in case of EGR. In particular, the wear amounts with EGR were considerably higher than those without EGR at 90 and 110 mm from the top. Based on the above data, all the measured wear amounts were converted by defining the spot without EGR 30 mm away from the top as a wear rate of 100%. The relative percentage of the measurement is presented in Fig. 4, where it is shown that in no EGR condition, spots closer to the top produced higher wear rate, and that in case of EGR, distances greater than the spot 60 mm away from the top had higher wear rate, with the highest wear rate at 110 mm from the top in this study.
