4.1 Structure
Comprehensive measurements of the stress level in the structure were carried out, and our calculations were verified. The results are compared with measurements from the well-proven K90MC-C engine type in Figs, 11 and 12.
4.2 Bearings
The bearings were inspected after the testbed trial and found to be in fine condition, as shown in Fig.13.
4.3 Temperature Level of the Combustion Chamber Components
A substantial temperature reduction on the gas side of the piston crown was one of the main objectives when the new combustion chamber (see Fig.6) was introduced.
The best compromise between the important parameters: gas side surface temperature, oil side surface temperature, mechanical integrity and ease of overhaul, turned out to be the forged, bore cooled OROS piston crown with high topland. The combustion chamber temperatures were found to be very moderate, see Fig.14, giving a high safety margin against hot corrosion.
On the coolant side, the piston temperatures were well below the limit where coke formation from cooling oil would be expected. Thanks to the lower gas side temperature, Inconel welding on the top of the piston can be dispensed with. The temperature level in the piston ring grooves ensures safe operation without carbon formation.
The liner temperature was in accordance with the calculated value, avoiding cold corrosion and giving a wide margin against heat cracks. The temperature level of the Nimonic exhaust valve will secure the expected lifetime of the spindle as well as the expected hours between overhaul.
During the last few years, we have experienced exhaust valves in service with a lifetime of more than 30,000 hours, in spite of a temperature level much higher than the level measured on testbed for the K98 engines.
4.4 Inspection of Combustion Chamber
The result of the scavenge port inspection after 800 hrs. can be seen in Fig.15, and the following comments can be added:
・Piston rings were all found to be in good condition with nice and smooth running surface
・No deposits on any of the ringlands and good cleanliness
・Piston topland had dry grey deposits and no sign of polishing
・Cylinder liners were all found in good condition, with the wave-cut marks intact in the visible lower part of the liner. No rib marks, no cold corrosion, and no micro-seizure were found.
The exhaust valve was dismantled and found to be in good condition and subsequently reinstalled, see Fig.16.
