TS-153
Disclosure of Journal Movement Behavior in Main Bearing of Large 2-stroke Marine Diesel Engine
Iwao SUGIMOTO*, Shinji BABA**, Tadashi KAWASAKI**, Tatsumi ONAKA**, Masao YATSUO*** and Haruo TANAKA***
ABSTRACT
For improving the reliability of main bearing in large 2-stroke marine diesel engine, it is indispensable to clarify the effect of uneven alignment between two adjacent main bearings. We have studied to disclose the journal movement behavior in main bearings. Firstly, the journal movements in main bearings of actual engines were measured. The journal center locus and the journal tilting angle were clarified. Secondly, a theoretical calculation model has been developed in order to simulate the journal movement behavior under uneven alignment between two adjacent main bearings. For confirming the validity of the model, calculated results were compared with measured results. The model was proved effective to simulate the journal movement in high accuracy. At last, the journal movement under uneven alignment has been simulated, and an adjustment procedure in case of misaligned journal on actual engine has been confirmed with efficiency.
Key Words: Diesel Engine, Journal Beating, Measurement, Computational Mechanics, Transfer Matrix Method, Mobility Method, Alignment, Journal Center Locus, Journal Tilting Angle
1. INTRODUCTION
Uneven alignment between crank journal and main bearing in large 2-stroke marine diesel engine decreases bearing load capacity. In some extreme cases, bearings will be damaged. Furthermore, recent large 2-stroke marine diesel engine has been developed for more powerful, longer strokes, lighter mass and in a more compact size. As for main bearing of the diesel engine, the higher degree of specifications is required. Combined with these performances of engine, a careful adjustment of alignment between journal and main bearing is required more strictly than before, especially when installing an engine in a vessel. Therefore, for improving the reliability of engine, it is indispensable to keep the alignment under optimum conditions free from damage.
As for the quality control of the journal alignment in assembling, crank deflection measurement and bearing load measurement by jacking up in static condition have been carried out. By comparing the measured results with established quality range, the main beating has been kept up with reliability. If the result is out of the range, another main beating with a different thickness will be installed to adjust the alignment. However, the effect of adjustment by reinstailing the different thickness of bearing has not been measured from actual engine.
The objective of this study is to disclose journal movement behavior under uneven alignment between journal and main bearing. In the beginning, the journal movement behavior such as journal center locus and journal tilting angle was measured in several main bearings. Secondly, a theoretical calculation model has been developed in order to simulate journal movement behavior under uneven alignment between two adjacent main bearings on a vessel. Then, to evaluate the validity of the calculation model, the calculation results were compared with measured results. At last, the beneficial effect of adjustment based on the actual procedure has been confirmed.
2. MEASUREMENT IN ACTUAL ENGINE
2.1 Measurement Method
2.1.1 Measurement Main Bearing
Figure 1 shows the measurement main bearing. Journal movement behavior is detected by four gap sensors fitted in an upper part of bearing. Thermocouples are used for compensation of the gap sensors.
Figure 2 shows the definition of journal center and journal tilting angle. Assuming that the distance between the gap sensor position and the center of the bearing is invariable and that there is no bearing deformation, journal center is calculated by geometrical method. By the measurement bearing, two journal center points both at fore side and at aft side of the bearing are measured at the same time. As the results of the two journal center points, relative journal tilting angle between the journal and the bearing is calculated.
2.1.2 Specification of Engine and Operating Condition
Table 1 shows the specification of engine. The type of the engine was selected as most popular one in our production. The measurements were carried out during the delivery test operations. The operating condition was based on propeller law characteristics from 0% to 100% load.
*Technical Research Institute, Hitachi Zosen
2-2-11 Funamachi, Taisho-ku, Osaka 551-0022 JAPAN
FAX: +81-6-6551-9849
E-mail: sugimoto@mech. lab.hitachizosen. co.jp
**Hitachi Zosen
***Hitachi Zosen Diesel and Engineering
