4. HIGHER EFFICIENCY AND NO REDUCTION
Since a compact and high-efficiency engine can be realized by increasing the maximum combustion pressure (Pmax) as shown in Fig, 3, Pmax of the new medium-speed engine series were improved by 11% as compared with conventional engines.[2] The engine produces greater output with an optimized cooling system and structure realized from structural analysis and component tests to withstand subsequent increases in thermal and mechanical loads. Endurance tests were conducted for more than 500 hours under O% to 110% load conditions to verify the durability of each component. (Fig.4)
For reduction of NOx emission, various miscellaneous features (ex. Exhaust gas re-circulation etc,) are now available, but we have taken the unique approach -- of engine tuning -- toward clearing the IMO primary regulation values. This method avoids the efficiency losses. [3]
In consideration of engine performance, optimized specifications of the engine were obtained using simulation software for general-purpose engine performance. Parameters such as compression ratio, fuel injection timing, boost pressure, and intake valve close timing are included in the simulation. (Fig.5.)
This simulation suggested that a combination of the following techniques would be effective in reducing NOx emission, without attendant reduce efficiency:
1. Increasing boost pressure
2. Retarding intake valve close timing
3, Increasing compression ratio
4. Optimized fuel injection timing.
Fig.7 Trend of Lub. Oil Property
Simulation results were applied to an actual engine, the model 28HLX. The compression ratio was increased 10%, overlap was advanced 12deg CA, intake valve close timing was retarded 20deg CA, and boost pressure was increased 15%.
As a test result, all engines cleared the IMO NOx regulation by comfortable margins, without adversely affected fuel consumption. In test cycle E3 results of actual engines are shown in Fig.6.
5. REDUCING LUBRICATING OIL CONSUMPTION
Lubricating oil consumption (LOC tends to increase as engine output increases. Conventional attempts to solve this problem - by improvements in ring pack, cylinder liner materials, and cylinder surface roughness and by altered piston profile -- were not significantly effective.
Recently, however, a number of successes have been reported, one of which is a fire ring inserted into the upper part of the cylinder liner to reduce lubricating oil consumption. [4] [5]
