In this paper we aim to highlight the developments of slow speed diesel engines in the last decades and the effect of that on improving engine thermal efficiency and lowering specific fuel consumption to approach the economic operational ship cost Statistics and tables have been used to reveal this point. Sulzer RTA, Burmister & Wain MC and Mitsubishi UE engines are considered as examples during this analytical, which is a fact in today's diesel engine market The recently marvelous progress of slow speed marine diesel engines for reappraisal of energy rejected from the cycle is the result of getting together a lot of technical parameters. 1. Firstly, improvement of engine systems and performance: The increase in turbocharger efficiency and using constant pressure systems of exhaust gases to get higher air flow rate and lower exhaust gas and engine components temperature are discussed. The factors affecting the design of variable injection timing mechanism to reduce fuel consumption at part loads are explained. Several designs with different engine modules are examined. By controlling the ratio of maximum pressure to mean effective pressure a reduction of specific fuel consumption can be achieved. 2. Secondly, developments of diesel engine parts. As a result of increasing the output power per cylinder and maximum combustion pressure, the diesel engine parts are subjected to sever thermal and mechanical loads. Efforts of engine makers for developing engine parts are discussed. A survey of the up-to-date modern design diesel engine parts is furnished. The factors affecting the design of variable injection timing mechanism to reduce fuel consumption at part loads arc explained several designs with different engine modules are discussed. By controlling the ratio of max. pressure to mean effective pressure from · 7 to 10 reduction of specific fuel consumption by 10 gram I b. hp. is attended. 3. Secondly, developments of diesel engine parts. As a result of increasing the out put power per cylinder (～7,600 hp/cy/r) and max. Combustion pressure (～160 bar) the diesel engine parts are subjected to sever thermal and mechanical loads, the second part of this paper did a survey for the up to date modern design diesel engine parts and the following points were discussed: By introducing super-long stroke engine (L/D) · 4.0) progressive reduction in specific fuel consumption is obtained, and in the same times the max. combustion pressure is controlled. The application of bore - cooling in combustion chamber parts reduce the thermal load and improve engine performance. Modifications of inside piston crown to resist high combustion pressure are discussed. Welded crankshaft with high production technology reduces the weight of crank shaft by 30%. Due to high firing load, and long stroke engine, using one piece lower crosshead bearing shell can used for a large size engine. At the end of this paper ceramic-metal composite coated piston ring and cylinder liner for large slow speed engine are touched.
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