Igorova promišljanja (43) – Igor's Reflections, Summary in English Diesel engine at the beginning of 2015 The second half of 20th century witnessed the competition between slow speed two stroke and medium speed four stroke diesels as the ship main propulsion engines. Namely the advantage of the medium speed engine geared installations was shown in attainable lower propeller shaft speed and accordingly higher propulsion efficiency, particularly in the propulsion of relatively slow speed vessels like large tankers and bulk carriers. When after year 1980 was generally adopted the exhaust valve and uniflow scavenging of two stroke diesels, followed by ever increasing piston stroke and diameter ratio s/d, enabling substantial lowering of engine speed, the competition ceased and directly coupled slow speed two stroke diesel triumphed. In the article is reviewed recent MAN Diesel building programme both of the slow speed two stroke and medium speed four stroke engines. The main particulars of the exposed engines are discussed in view of their suitability for both the direct propulsion and ships auxiliary purposes. The absolute maximum in terms of the output reaches 12-cylinder G95ME-C9 engine developing power MCR of 82 440 kW at 80 rpm and at a mean effective pressure as high as 21 bar. However such powerful engine entails questions of its suitability for ship propulsion, particularly regarding the screw propeller which should absorb and transform so high power. Ultra long stroke engine G80ME-C9 has reached a speed of 72 rpm at point L1 and 58 rpm at L4, which is absolute minimum among diesels of today. Therefore is most suitable for the propulsion of ULCC and VLBC respectively. Thus a 9-cylinder engine 9G80ME-C9 is developing MCR = 42 390 kW at 72 rpm while, for comparison, VLCC Batillus of 553 662 dwt had two steam turbines 2 23 900 kW and 86 rpm at propeller shaft. Diesel engine layout diagram is discussed, mentioning its early introduction in nineteen-sixties, aiming to better understanding and use of terms like MCR, SCR, SMCR, OR, as well as choosing combination of speed and power within the layout diagram. As regard the medium four stroke diesels it is reasonable to expect further development of the engine with magic 600 rpm suitable for both frequencies, i.e. 50 and 60 Hz respectively.
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