In recent years, the flow coefficient of injection nozzles has been increased in order to improve output and performance of diesel engines.
The authors have studied the relation between flow coefficient and rounding-off of nozzle hole inlets. The nozzle with proper non-dimensional R: more than 0.3, are getting stable and increasing about 20% of the flow coefficient.
The proper nozzle hole diameter of the rounding-off nozzles are smaller than the conventional ones. The engine performance with these nozzles also improved because of the better injection and spray characteristics in wide load range, especially fuel consumption and exhaust smoke. The main factor shall be considered cutting-off of after-burning from the injection and combustion analyses.
These nozzles shall be also expected to prolong endurance time because of preventing hole deformation.

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This paper discusses the tentative calculation method for simulating the heat release rate which is indispensable for predicting the medium speed diesel engine performance. The combustion tests were conducted in the medium speed diesel engines with 220mm and 240mm bore using the marine diesel fuel oil and the degraded heavy fuel oils, and the relationship between the cumulated quantity of fuel injection rate and the cumulated quantity of heat release rate obtained from those tests is examined. The results indicate that the shape in the unburnt quantity mode of fuel injected into the combustion chamber is divided into three stages, and the first and the second stages can be approximately shown as the linear function, the third stage can be approximately shown as the exponential function. Further, the heat release rate can be simulated by means of this calculation method using the coefficients and the exponents which are evaluated from the relations between the cumulated quantities, and using the input data for the fuel injection mode. And the agreement between the measured and the calculated heat release rate is found to be good in trend and in magnitude.

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In order to reduce the amplitude of the propeller shaft vibration, it is useful to apply the hydrostatic bearing to the stern tube bearing.
This paper describes the theoretical and experimental investigations on the reduction of the propeller shaft vibration by using a hydrostatic bearing.
The theory is based on the finite width hydrodynamics.
The calculated results give very good agreements with the measured ones. Also the hydrostatic bearing gives a high degree of reduction efficiency of vibration, which reduces the vibration amplitude to 60-70% of that of conventional type.

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We have analysed statistically on damage data of propulsive shaftings for the classed ships with Japanese flags by means of application of quantification theory. Then the effect of factors on the maintenance of propulsive shaftings has been studied quantitatively. The main conclusion obtained are as follows:
(1) The amount of maintenance in water lubricated type has a tendency to become larger than that in oil lubricated type irrespective of other factors.
(2) The amount of maintenance in water lubricated type shows time-dependent trend; it generally takes little cost within 4 years but much becomes to be required after that. Then, with the lapse of time the factors other than ship's age extend their influence on the amount of maintenance.
Those factors are ranked as power of engine, ship's age, kind of cycle, propeller revolution, coupling type of shaft in order of decreasing influence.
(3) The amount of maintenace in oil lubricated type is affected by 5 factors as well as in the case of the water lubricated type. Their ranks are, however, as propeller revolution, coupling type of shaft, power of engine, kind of cycle, ship's age in the order of decreasing influence. The factor, ship's age, which is ranked higher in water lubricated type, is the bottom rank. In other words, this type shows time-independent trend contrary to the water lubricated type. Next the affect of categories in each factor on the amount of mainterance has been examined.For example, as the power of engine increases that has both effects diminishing and increasing the amount of maintenance in water-lubricated type and oil-lubricated type, respectively. Propeller revolution and coupling type of shaft are listed as the factors which have adverse effect such as power according to the lubriated type.
(4) It has been shown that the amount of maintenance can be illustrated as Fault Tree diagram by means of influential factors, and consequently represented as the structure function considering their influential vector.
(5) It has been shown that the amount of maintenance can be represented as Fuzzy Set by transforming structure function and probability distribution function or value of exceedence probability function into element value and membership function, respectively.

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A new system has an intention to give a navigator on watch-keeping duties knowledge of failure diagnosis for an engine. The system will become to be necessary with the development of control systems for marine engines. An engineer on board ship can directly give the diagnosis knowledge of the engine. The relation among knowledge bases is represented with petri net model. The input-knowledge bases can easily be changeable during navigation if necessary. When the engine system gives an alarm, a navigator can easily run this system and diagnoses the failure of the engine by this system.
This system applied to the training ship “Yuge maru” has shown effective results.

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We studied to the calculation method of the carbon distribution and ring content of diesel fuel oils from measurements of specific density 15°C, kinematic viscosity cSt @50°C and sulfur content wt % in conformity to ASTM Standard D 3238-85.
Consequently, from the calculating contents of aromatic ring structures (%C_A), naphthene ring structures (%C_N), paraffin chains (%C_P), and CCAI, We were able to classify the quality (straight, cracking, visbreak and FCC) and to decide the propriety of blending of diesel fuel oils.

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