Excessive wear and/or scuffing on piston rings and cylinder liner may occur due to unexpected combustion characteristics of the marine fuel oil in large marine diesel engines. In order to predict and prevent damage due to combustion in advance, an analysis of the flame was tried using a constant volume vessel for visualization of combustion. To observe a flame accurately, a stable fuel injection system is needed. This paper describes the development process of such a fuel injection pump.
Marine fuel oil is generally supposed to be free of used lubricating oil, but bunker oil sometimes contains used oil. Treatment of waste oil generated on board ships is very important. Although waste oil is usually burned up in an incinerator, such waste oil as used lubricating oil is sometimes mixed into fuel oil and reused as energy. This paper reports a study of the combustion characteristics of fuel oil mixed with engine oil used in-house. We found that harmless combustion of fuel oil containing 5% or less used engine oil is possible.
The crosshead bearing in large two-stroke diesel engines operates under severe lubrication conditions because hydrodynamic action is limited by low-amplitude, low-velocity oscillation under high specific load. The recent trend toward more compact engines with increased output raises the bearing specific load, thereby significantly increasing the lubrication severity. Therefore it is very important to find a means of preventing seizure of the crosshead bearing. In this study we evaluated a technique for monitoring abnormal vibration using a dynamically loaded bearing seizure test rig capable of simulating load patterns and relative oscillations of the crosshead bearing in actual engines. Vibration spikes occur around the crank angles of ±90 degrees where the oscillating speed is zero during each cycle. When the lubrication severity increases, an abnormal vibration spike caused by severe metal-to-metal contact is frequently generated at a crank angle of approximately 90 degrees, where the oil film thickness reaches a minimum. If running-in is properly carried out immediately after detection of the abnormal vibration, the bearing surface is conformed, thereby eliminating the severe metal-to-metal contact. This monitoring technique for abnormal vibration can be an effective means of preventing seizure of the crosshead bearing.
The CGF (Continuous Grain Flow) forging method is widely applied to crankshafts of high-speed marine diesel engines in recent years. CGF-forged crankshafts are considered to have an advantage in fatigue strength compared with free-formed forged crankshafts because of two factors: 1) continuous grain flow along the axial direction of the shaft, and 2) small segregation of impurities in the surface layer of the shaft. In general, however, the forged grain flow of CGF-forged crankshafts has a local discontinuation at the fillet between the crank-pin and the crank-arm or between the crank journal and the crank-arm, which originates in the shaft machining process. In this study, effects of the local discontinuation of the forged grain flow on the ultra-high-cycle fatigue strength were investigated by fatigue tests and by FEM calculations. Based on the investigation, it is clear that the effects of continuous grain flow on the fatigue strength are invalid in the event that a local discontinuation of the forged grain flow at the fillet exists.