디젤 주기관의 DERATING에 관한 연구

Abstract

As a movement of cargo and passenger is increasing in currently, the transportation of the vessel occupies much of them. To the vessel, the source power has been very important to propel the vessel as well as the space of the cargo. Therefore, it was interested to owner and manufacturer to take the cheaper and more efficient engine which is suitable for the vessel.

Ship's main power source is called 'Main Engine', and that must be selected properly because it is the one of the most important equipments. In the matter of the designing of the ship or saving the expense, the efficiency of the main engine is very important. So there are some requirements should be satisfied as the main engine, which are the low SFOC(specific fuel oil consumption), low malfunction and high reliability, convenient maintenance and low maintaining expense, easy operating, low efficiency reduction despite long-term use, a few number of crew in the engine room, light weight and small volume, low vibration and noise, cheap price, and so on. But there is nothing to be satisfy all these requirements.

The main engine will be developed and taken in the vessel, which has a output from a few horsepowers to more than 130,000 BHP (MAN B&W 14K 108MC & ME ENGINE). The oil crises in 1973 and 1979 caused considerable effort to decrease the fuel consumption. As a result, the main engine is being changed through the shape(from loop scavenging air system to uniflow scavenging air system), higher compression ratio, low speed and long stroke. The operation system also being changed cam shaft controlled engine into electronically controlled engine. The changes of this sort contribute to not only a improvement of the SFOC as a final object, but also a decrease of air-pollution for healthy life as a common object. If the main engine is producted and supplied in need of various condition, it's the best ideal. It is difficult to make a various engine satisfied with all factors, various cargo, adaptability in various weather condition, change of navigation condition, a various request of owner, expended cargo area according to owner's request, change of oil price, etc. The engine manufacturers have tried to get a solution to satisfy consumer's request. So they could find a way that can change the rating through large range from the engine already manufactured. The ways changing the rating are modifying scavenging air pressure, adjusting the compression ratio through changing compression shim, adjusting the timing of exhaust valve and modifying a diameter of nozzle of fuel injection valve etc. These ways are tried through large range to change rpm to 72% and engine's output to 48% of MCR with keeping the normal engine's shape almost. The important elements considered in the process of derated output of the main engine are not only about safety and extension of machine's length of life, but also about how can you recover the beginning overcapitalization as soon as possible through low SFOC. And then these act also have to fit the profit among owner, manufacturer, and operator.

At the study, try to compare and consider between rating and derating through this research with several data about modifying rating which have been done by engine manufacture so far.

So this study shows,

- definition of the rating

- producing basis and analysis of each of the graph which constitute load diagram which is used for setting the limitation of a load for the successive operating of the main engine

- the relationship between engine output and rpm

-the relationship between engine torque and mean effective pressure

- engine derating that should be done and consideration of the method

- a strong point and a weak point when engine derating

- the interrelation in the matter of expense in long-time operation

- the propeller efficiency when engine derating

-the item that should be consider when engine derating

and it had been chosen the various comparative standards and make several ships(used for derating) which had been made by differing manufacturer an object of scientific study, and then it had been compared and examined difference with regular engine.