Effects of nozzle diameter, fuel injection pressure, density of ambient gas and impingement on a wall, on fuel distributions in unevaporated diesel sprays were investigated. The fuel distributions were obtained by means of the image analyses of shadow photographs of sprays. Further, effects of fuel injection pressure on combustion of sprays in a diesel engine and a relation between fuel distributions in unevaporated sprays and the heat release rates in the diesel engine were investigated. The results are as follows. Decrease in nozzle diameter, increase in fuel injection pressure and impingement on a wall improve fuel-air mixing. Increase in fuel injection pressure improves the performance of the diesel engine. There is a considerable correlation between the fuel distributions in unevaporated sprays and the heat release rates in the diesel engine.

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The ignition process of fuel sprays into high pressure high temperature atmosphere has been studied experimentally and theoretically, and a new concept for the ignition process has been proposed. From the experiments, it has been found that the ignition of fuel spray occurs at the stagnation region of the fuel spray tip. The stagnation velocity gradient at the fuel spray tip, proportional to the fuel spray tip speed and inversely proportional to the fuel spray tip width, decreases rapidly with time from the start of fuel injection or with distance from the fuel nozzle tip. Based on the experimental results, a new model for fuel spray ignition has been proposed. The equations governing ignition phenomena in the stagnation flow field have been solved by the asymptotic method to obtain the ignitable limit and ignition time in the stagnation region at the fuel spray tip. The ignition behavior of the fuel spray can be well explained by considering the effects of the stagnation velocity gradient at the fuel spray tip on the ignition reaction time of the fuel-air system. The ignition delay of a fuel spray is divided into two parts: one is the time spent for reducing the velocity gradient at the spray tip below the critical velocity gradient for ignition; the other part is the time for an ignition reaction at the given velocity gradient. Since the latter is much smaller than the former, most of the ignition delay is time for reducing the velocity gradient at the fuel spray tip below the critical velocity gradient for ignition. The ignition delay of diesel sprays can be predicted fairly well by using the above concept.

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This paper describes for the exhaust smoke study by the degraded heavy fuel oil combustion in 220mm bore medium speed diesel engine. The combustion test has been carried out on the heavy fuel oil (490 cSt at 50°C) from Visbreaking units. It is experimentally clarified that the exhaust smoke is affected by the fuel injection and the air charge components which govern the fuel spray penetration in the combustion chamber. It is suggested that the exhaust smoke measured under low load condition was related to the excess fuel in the fuel spray fraction impinging on the piston wall at the time of ignition which was estimated from the fuel spray penetration on the momentum theory.

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Following to the recent trends of low fuel consumption, high output and fuel diversification such as heavy fuel use, diesel engine components are exposed under increased load and temperature.
The components in the combustion chamber which are subjected to both thermal and mechanical load simultaneously are required higher reliability.
In particular, exhaust valve which is one of the highest temperature components is subjected to more severe condition than others.
The authors have studied to improve reliability of the exhaust valve used under above mentioned condition.
In order to reduce mechanical stress, especially on valve head, FEM calculations as well as stress measurements have been conducted and an optimum shape of valve head was proposed.
As for the corrosion resistance of exhaust valve used with heavy fuel, experiments have been made both in laboratory and on test engine.
A Nimonic valve is one of the best solution, today, for both stresa resistance under high temperature and corrosion resistance.

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Centrifuges has been used for purifying marine fuel oil. And recently, marine fuel oil has been increasingly degraded due to higher density, viscosity and sludge concentration as well as entrainment of catalyst particles.
In order to cope with the poor-quality fuel oil, more than 150 sets of dacanter-type oil purifiers, which have never been used before, have already been installed aboard vessels, and disc-type oil purifiers and systems, which are capable of automatically judging and executing operations replacing operators, have come into use.
Described herein are the outline of structures, principles, features, performance, etc. of these decanter-type and disc-type oil purifiers.

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