On the other hand, as shown in Fig.2, principal particulars of diesel engines such as brake mean effective pressure are approximately doubled during the last several decades and so load conditions of engine components are getting more sever.
Under these conditions, safety factors of components equal to or even higher than those of previous engines could be ensured by actively using know-how and technologies which had been accumulated through the development of diesel engines up to that time as well as the newest analyzing methods in order to keep the reliability of the UEC52LSE engine.
4. STRUCTURAL FEATURES
Fig.3 shows the sectional drawing of the UEC52LSE engine. This engine was designed, based on the design concept of the UEC-LS II engines with good service results.
Compactification such as pipeless structure was also promoted. The main structure of the UEC52LSE engine incorporated various kinds of improvements in order to realize the before-mentioned development concepts, reflecting the design concept of the own designed 4-stroke KU diesel engines.
The main structure of the UEC52LSE engine will be explained as follows.
4-1. TURBOCHARGER ARRANGEMENT
Two kinds of turbocharger arrangement have been prepared to allow to select either the ordinary exhaust side or aft side of the engine in order to design the best engine arrangement and to plan a flexible engine room for engine rooms of diversified ship types. (See Fig.3.) For example, the aft side turbo charger arrangement with smaller width is considered to be suitable for engine rooms of slimmed ships.
This engine uses the high-performance MET-SE type turbochargers developed in-house and thus high efficiency of this engine can be kept.
4-2. ENGINE STRUCTURE
This engine has highly rigid structure by firmly tightening its bed plate, column and jacket, each of which is a one- piece casting, with tie rods. The camshaft case is cast in one piece with the column.
Reduction in the number of components and improvement in accessibility and maintainability have been achieved by realizing pipeless structure which integrates hydraulic oil pipes for exhaust valves and lubricating oil pipes for the camshaft system in the column. The jacket is of highly rigid structure with large height and can support cylinder liners directly.
Thanks to this structure, cylinder cover bolts have been shortened and made rigid compared with previous engines.
In addition to this, rigidity has been kept for supporting parts of various equipment and structures on the upper part of the engine including upper grating.
Thus the local vibration of the upper part of the engine has further been reduced.
4-3. CYLINDER LINERS
The liner is made of special cast iron and upper part of the cylinder has large thickness in order to stand high maximum cylinder pressure.
A jacket cooling system without cooling bores could be adopted by optimizing cooling water flow through analyses of liner temperature, stress and water flow by FEM analysis. Thus, structure has been simplified. For scavenging ports at the lower part of the cylinder liner through which fresh air flows into the liner, the strength of air swirls has been optimized relative to the height of ports, by adopting the newest CSS (Controlled Swirl Scavenging) ports developed by the company. Thus, combustion conditions of this engine have been improved due to its high scavenging efficiency.
4-4. PISTONS
The piston is made of special alloy, and has adopted midway supporting structure which can stand high thermal loads due to high maximum cylinder pressure and high brake mean effective pressure.
The inner side of the piston is effectively cooled with system oil with optimized flow speed. Thus, piston temperature and stress levels could be kept in the proper range.
4-5. MAIN BEARINGS
The oil film characteristics of the bearing have been able to be evaluated accurately by the oil film characteristics analyzing method (EHL: Elasto Hydrodynamic Lubricating) taking account of rigidity around the bearing.
Thanks to this evaluation, white metal with excellent embed debility and reliability has been used same as previous engines. The bearing is of a thin metal type as before and emphasis has been put on ease of maintenance.
4-6. CAMSHAFT DRIVING SYSTEM
The camshaft is driven by the crankshaft through a gear train which has high reliability and high accuracy of timing same as previous engines. The reliability of this engine has been further improved and the number of components has been decreased by integrating the camshaft case into the column and decreasing the number of driving gears from four for previous engines to three.
4-7. AIR COOLER
The air cooler is of one-piece structure with its casing. There is open space above the air cooler to facilitate its overhaul and transport. Thus, maintainability has been improved.
Thanks to the simplification of engine structure with the aim of improvement in reliability and maintainability, the number of components of the UEC52LSE engine could be decreased by about 25 percent in comparison to the previous UEC50LS II engine.
5. DESIGN VERIFICATION OF PERFORMANCE AND RELIABILITY
Increase in brake mean effective pressure and mean piston speed for increasing engine output, and the same in maximum cylinder pressure for economical fuel consumption not only make thermal loads around combustion chambers severe but also have big influence on the strength of structural components and main moving parts of engines.
In the development stage of this engine, design verification was therefore implemented in all aspects, actively using technologies which had been accumulated through the development of diesel engines in the company over many years as well as the newest knowhow. A part of design verification is explained as follows.
5-1. STRENGTH OF STRUCTURAL COMPONENTS
Fig.4 and 5 show results of analysis for structural components of the UEC52LSE engine. For bed plate, column and jacket, FEM analyses have been implemented using three-dimensional solid models for one and half cylinders. Stresses and deformations at various points of these components have been calculated and fluctuating values of acting stresses have been evaluated under major load conditions at the time when tie rods are tightened, TDC and BDC, maximum cylinder pressure is acting, and maximum side thrust force is acting.
Thus, it has been confirmed that fatigue safety factors and rigidity of these components are the same as or even higher than those of well-established previous engines.
