Many machines including marine diesel engines and plants are operated while maintaining their functions and safety through inspection and maintenance. At the present time, time-based inspection and maintenance practices are generally adopted. However, a more effective inspection and maintenance scheme that reflects the present economic situation is required. As such, a risk-based inspection/maintenance (RBI/RBM) technique for electric power plants is introduced. This technique is regarded as an efficient method of maintaining machine and plant safety within the limits of cost and manpower. On the other hand, RBI/RBM has not yet been applied to marine diesel engines. To apply RBI/RBM to a marine diesel engine, risk evaluation should be conducted first. In this paper, risk evaluation of a marine diesel engine was performed based on a database of ship failure.

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海上輸送中の荷役の安全の観点からは，ばら積み貨物としての天然ガスハイドレートペレット（NGHP）の分解によって，貨物温度が急激に低下する現象が起こらないことを確認することが重要である．このためには、NGHPの安全かつ経済的な輸送という意味において，NGHPの分解速度が充分に低い温度領域の下限界（DLT）が存在するか否かを確認する必要がある．しかしながら，現時点では天然ガスハイドレート（NGH）の自己保存性メカニズムに関する知見が充分でないため，NGHPのDLTを理論的に決定することができず，実験によって見積もらざるを得ない． 著者らは，温度範囲-35℃～-5℃，大気圧条件下で，擬似断熱状態とした試料ペレット50個の分解挙動を計測するための実験装置を設計・製作した．MHP及びNGHPは分解によってその温度が初期状態から下がる性質を有するため，ペレットの分解に起因する温度低下によりペレットの分解反応が加速され，その結果としてますますペレットの温度が下がる可能性がある．安全上問題のあるこうした現象が実際に起こるか否かを確認するため，著者らは，上述の実験装置を使用して，擬似断熱状態下におけるメタンハイドレートペレット（MHP）の分解速度と温度との関係，ペレットの初期ガス包蔵量が分解速度に及ぼす影響などについて調べた．今回実施した24時間の擬似断熱実験では，（初期ガス包蔵率が高く分解速度も大きい）ペレット製造後の経過日数の浅いMHPを対象とした場合においても，荷役の安全上問題となる現象は見られず，DLTの存在も確認されなかった．さらに，大気圧条件下では化学的に不安定な状態にある試料ペレットのハイドレート化率を精度良く推定する手順について検討し，その妥当性（ペレット数量，ばらつきの評価など）を確認した．

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A series of experiments was performed on a circulating fluidized bed (CFB) in order to investigate effects of the ship motion on gas-solid heat transfer in the riser. Superficial velocity, rolling period and inclination angle were varied in the experiments, while amplitude of the rolling motion was fixed at 15deg. The following results were obtained: (1) At upright attitude, local heat transfer coefficient in the lower part of the riser had a large scatter in the bubbling fluidization mode, because suspension density had a steep gradient along the vertical direction. In the upper/mid part of the riser, on the other hand, scatter in the local heat transfer rate is negligible. (2) At inclined attitudes, except for the riser bottom in the bubbling fluidization where particle motion was locally suppressed by inclination locally, heat transfer rate at lower side of the riser wall was larger than that at upright attitude, and heat transfer was promoted with the increase of inclination angle. (3) When the CFB underwent rolling motion, heat transfer coefficient at the riser wall was augmented. Considering scatter in the local heat transfer coefficient, the rolling period had almost no effect on heat transfer at the riser wall. Therefore, it is concluded that gravity plays a dominant role in heat transfer at the riser wall.

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Improvement of a ship's energy system is required for better fuel oil economy and environmental sustainability. The authors proposed a concept of heat recovery system from exhaust gas for a marine diesel engine. Core device of the system is a circulating fluidized bed (CFB) heat exchanger with desulfurization function. In this report, adjustments to the "Circulation Type", in which a condenser was added, were evaluated to gain more electrical power generated from the exhaust gas heat. Analysis of the "Circulation Type" connected to a 1400kW 4-stroke marine engine showed that the maximum electrical output of "Circulation Type A" system, consisting of the CFB and a steam-turbine generator, was 2.96%at 75%-loaded power in the engine. On the other hand, the maximum electrical output for "Circulation Type B" system, consisting of the CFB, a superheater and two generators, and "Circulation Type C" (preheater was added to "Circulation Type B") was up to 8.47%, and 9.20%, respectively. In addition, net electrical output, total heat transfer surface, and total volume of heat transfer regions at each system were also estimated. The total volume estimation in particular, showed that the CFB contributed to the miniaturization of the waste heat recovery system.

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Particulate matter (PM) exhausted from diesel engines has several serious effects on human health and the environment. In this study, collection efficiency of the electrostatic-cyclone Diesel Particulate Filter (DPF) was evaluated to reduce the PM emission from marine diesel engines. A three-cylinder high speed four-stroke marine diesel engine was used as the test engine. The effects of exhaust gas temperature at the DPF inlet, exhaust gas flow rate through the DPF, applied voltage of electrostatic precipitator and operating condition of the engine on the PM collection efficiency were examined. Experimental results show that the exhaust gas temperature has a strong effect on the PM collection efficiency and that the PM collection efficiency at propeller load is higher than that at constant speed operation.

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