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Contents Combined Marine Propulsion Plant ................................................................................................................ 2 1.

Combined diesel or gas (CODOG) ......................................................................................................... 2

2.

Combined diesel and gas (CODAG) ....................................................................................................... 3

3.

Combined diesel-electric and gas (CODLAG) ....................................................................................... 4

4.

Combined diesel and diesel (CODAD) ................................................................................................... 5

5.

Combined steam and gas (COSAG) ........................................................................................................ 5

6.

Combined gas or gas (COGOG) ............................................................................................................. 6

7.

Combined gas turbine and gas turbine (COGAG) .................................................................................. 7

8.

Combined gas and steam (COGAS)........................................................................................................ 8

9.

Combined Nuclear And Steam propulsion system (CONAS) .............................................................. 10

Reference....................................................................................................................................................... 10

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Combined Marine Propulsion Plant 1.

Combined diesel or gas (CODOG)

This is a type of propulsion system for ships that need a maximum speed that is considerably faster than their cruise speed, particularly warships like modern frigates or corvettes. For every propeller shaft there is one diesel engine for cruising speed and one geared gas turbine for high speed dashes. Both are connected to the shaft with clutches, only one system is driving the ship in contrast to CODAG-systems, which can use the combined power output of both. The advantage of CODOG is a simpler gearing compared to CODAG but it needs more powerful (or more) gas turbines for the same maximum power output and also the fuel consumption at high speed is even worse compared to CODAG.

Fig.1 Combined diesel or gas (CODOG) Reference Ships:         

MGB 2009, a prototype Motor Gun Boat of the Royal Navy (1947), and The two German torpedo boats Pfeil and Strahl (Vosper class, 1963-65) The Swedish Spica class motor torpedo boats (First vessel commissioned in 1966) The US Coast Guard Hamilton class cutters (from 1967) Finnjet (the World's fastest passenger ferry) Queen Mary 2 Halifax Class Frigates of the Royal Canadian Navy Bremen class frigates, and Brandenburg class frigates of the German Navy 2

        

Anzac class frigates of the Royal Australian Navy (RAN) and Royal New Zealand Navy (RNZN) other MEKO type frigates or corvettes Peder Skram class frigate of the Royal Danish Navy Pohang class corvette of the South Korean Navy Visby class corvette of the Swedish Navy Shivalik class frigate of the Indian Navy Niterói class frigates of the Brazilian Navy BNS Bangabandhu of the Bangladesh Navy Gepard class frigate of the Russian and Vietnamese Navies

2.

Combined diesel and gas (CODAG)

This is a type of propulsion system for ships which need a maximum speed that is considerably faster than their cruise speed, particularly warships like modern frigates orcorvettes.

Fig.2 Combined diesel and gas (CODAG)  

Principle of a CODAG system, with two speed diesel gearboxes It consists of diesel engines for cruising and gas turbines that can be switched on for high-speed transits. In most cases the difference of power output from diesel engines alone to diesel and turbine power combined is too large for controllable pitch propellers to limit the rotations so that the diesels can continue to operate without changing the gear ratios of their transmissions. Because of that, special multi-speed gearboxes are needed. This contrasts 3

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

 

3.

toCODOG systems, which couple the diesels with a simple, fixed ratio gearbox to the shaft, but disengages when the turbine is switched on. E.g. for the new CODAG propulsed Fridtjof Nansen class frigate of the Royal Norwegian Navy, the gear ratio for the diesel engine is changed from about 1:7.7 (engine:propeller) for diesel-only to 1:5.3 when in diesel-and-turbine mode. Some ships even have three different gear ratios for the diesel engines: one each for single diesel and double diesel cruises and the third when the gas turbine is engaged. Such a propulsion system has a smaller footprint than a diesel-only power plant with the same maximal power output, since smaller engines can be used and the gas turbine and gearbox don't need that much additional space. Still it retains the high fuel efficiency of diesel engines when cruising, allowing greater range and lower fuel costs than with gas turbines alone. On the other hand, a more complex, heavy and troublesome gearing is needed. Typical cruising speed of CODAG warships on diesel-power is 20 kts and typical maximal speed with switched on turbine is 30 kts. CODAG has been pioneered by Germany with the Köln class frigate.

Combined diesel-electric and gas (CODLAG)

This is a modification of the combined diesel and gas propulsion system for ships.

Fig.3 Combined diesel-electric and gas (CODLAG) A CODLAG system employs electric motors which are connected to the propeller shafts (usually 2). The motors are powered by diesel generators. For 4

higher speeds, a gas turbine powers the shafts via a cross-connecting gearbox; for cruise speed, the drive train of the turbine is disengaged with clutches. This arrangement combines the diesel engines used for propulsion and for electric power generation, greatly reducing service cost, since it reduces the number of different diesel engines and electric motors, requiring considerably less maintenance. Also electric motors work efficiently over a wide range of revolutions and can be connected directly to the propeller shaft so that simpler gearboxes can be used to combine the mechanical output of turbine anddiesel-electric systems. Another advantage of the diesel-electric transmission is that without the need of a mechanical connection, the diesel generators can be decoupled acoustically from the hull of the ship, making it less noisy. This has been used extensively by military submarines but surface naval vessels like anti-submarine vessels will benefit as well. Reference Ship:    

4.

Type 23 frigate (Royal Navy) F125 class frigate (German Navy) GTS Finnjet (Finnish cruiseferry) RMS Queen Mary 2

Combined diesel and diesel (CODAD)

This is a propulsion system for ships using two diesel engines to power a single propeller shaft. A gearbox and clutchesenable either of the engines or both of them together to drive the shaft.

Fig.4 Combined diesel and diesel (CODAD)

5.

Combined steam and gas (COSAG)

This is a propulsion system for ships using a combination of steam turbines and gas turbines to power the shafts. Agearbox and clutches enable either of the engines or both of them together to drive the shaft. It has the advantage of the 5

cruising efficiency and reliability of steam and the rapid acceleration and start-up time of gas. This system was mainly used on first-generation gas-turbine ships such as the Royal Navy'sCounty class destroyer and Tribal class frigate .

Fig.5 Combined steam and gas (COSAG)

6.

Combined gas or gas (COGOG)

This is a propulsion system for ships using gas turbine engines. A high efficiency, low output turbine is used for cruising speeds with a high output turbine being used for high-speed operations. A clutch allows either turbine to be selected, but there is no gearbox to allow operation of both turbines at once. This has the advantage of not requiring heavy, expensive and potentially unreliable gearboxes. The reason that a smaller turbine is used for cruising is that a small turbine running at 100% power is more fuel efficient than a bigger turbine running at 50% power. The system is currently used in the 3 ships of the Russian Navy's Slava class cruisers, and in the Royal Navy Type 42 destroyers. HMS Exmouth (F84) of the Royal Navy was converted to COGOG propulsion as a test bed for its use in later British ships.

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Fig.6 Combined gas or gas (COGOG)

7.

Combined gas turbine and gas turbine (COGAG)

This is a type of propulsion system for ships using two gas turbines connected to a single propeller shaft. Agearbox and clutches allow either of the turbines to drive the shaft or both of them combined. Using one or two gas turbines has the advantage of having two different power settings. Since the fuel efficiency of a gas turbine is best near its maximum power level, a small gas turbine running at its full speed is more efficient compared to a twice as powerful turbine running at half speed, allowing more economic transit at cruise speeds. Compared to Combined diesel and gas (CODAG) or Combined diesel or gas (CODOG), COGAG systems have a smaller footprint but a much lower fuel efficiency at cruise speed and for CODAG systems it is also somewhat lower for high speed dashes.

Fig.7 Combined gas turbine and gas turbine (COGAG) 7

Reference Ships:    

8.

Type 22 Frigate (Batch 3) (Royal Navy) Invincible-class aircraft carrier (Royal Navy) Hyūga class helicopter destroyer (Japan Maritime Self-Defense Force) Neustrashimy class frigate (Russian Navy)

Combined gas and steam (COGAS)

This is the name given to marine compound powerplants comprising gas and steam turbines, the latter being driven by steam generated using the heat from the exhaust of the gas turbines. In this way, some of the otherwise lost energy can be reclaimed and the specific fuel consumption of the plant can be decreased. Large (land-based) electric powerplants built using this combined cycle can reach conversion efficiencies of over 58%.

Fig.8 Combined gas and steam (COGAS) If the turbines do not drive a propeller shafts directly and instead a turboelectric transmission is used, the system is also known as COGES. COGAS differs from many other combined marine propulsion systems in that it is not intended to operate on one system alone. While this is possible, it will not operate efficiently this way, as with Combined diesel and gas systems when run solely on diesel engines. Especially COGAS should not be confused with Combined steam and gas (COSAG) power plants, which employ traditional, oil-fired boilers for steam turbine propulsion for normal cruising, and supplement this with gas turbines for faster reaction times and higher dash speed. 8

COGAS has been proposed as upgrade for ships that use gas turbines as their main (or only) engines, e.g. in COGOG or COGAG mode, like the Arleigh Burke class destroyers, but currently no naval ship uses this concept. However some modern cruise ships are equipped with COGES. E.g. Celebrity Cruises' Millennium and other ships of her class use turbo-electric plants with two General Electric LM2500+ gas turbines and one steam-turbine. BMW is currently researching combined gas and steam for automotive use, using their turbosteamer system. This uses the waste heat of combustion from the exhaust and turns it into steam to produce torque which is input into the crankshaft.

Combined cycle In electric power generation a combined cycle is an assembly of heat engines that work in tandem off the same source of heat, converting it into mechanical energy, which in turn usually drives electrical generators. The principle is that the exhaust of one heat engine is used as the heat source for another, thus extracting more useful energy from the heat, increasing the system's overall efficiency. This works because heat engines are only able to use a portion of the energy their fuel generates (usually less than 50%). The remaining heat (e.g., hot exhaust fumes) from combustion is generally wasted. Combining two or more thermodynamic cycles results in improved overall efficiency, reducing fuel costs. In stationary power plants, a successful, common combination is the Brayton cycle (in the form of a turbine burning natural gas or synthesis gasfrom coal) and the Rankine cycle (in the form of a steam power plant). Multiple stage turbine or steam cylinders are also common. Historically successful combined cycles have used hot cycles with mercury vapor turbines, magnetohydrodynamic generators or molten carbonate fuel cells, with steam plants for the low temperature bottoming cycle. Bottoming cycles operating from a steam condenser's heat are theoretically possible, but uneconomical because of the very large, expensive equipment needed to extract energy from the small temperature differences between condensing steam and outside air or water. However, it is common in cold climates (such as Finland) to drive community heating systems from a power plant's condenser heat. Such cogeneration systems can yield theoretical efficiencies above 95%. In automotive and aeronautical engines, turbines have been driven from the exhausts of Otto and Diesel cycles. These are called turbo-compound engines. Aside fromturbochargers, they have failed commercially because their mechanical complexity and weight are less economical than multistage turbines. Stirling engines are also a good theoretical fit for this application. In a combined cycle power plant (CCPP), or combined cycle gas turbine (CCGT) plant, a gas turbine generator generates electricity and heat in the exhaust 9

is used to make steam, which in turn drives a steam turbine to generate additional electricity. This last step enhances the efficiency of electricity generation. Many new gas power plants in North America and Europe are of this type. Such an arrangement used for marine propulsion is called combined gas (turbine) and steam (turbine) (COGAS).

9.

Combined Nuclear And Steam propulsion system (CONAS)

This is used on the Kirov class Guided missile cruisers. Complementary to the nuclear component there are two conventional boilers, installed as a backup in case of reactor failure. Both components are capable of driving two geared steam turbines, generating 120,000 hp (89 MW) at two prop shafts.[1] Reference 1. http://en.wikipedia.org/wiki/Combined_diesel_or_gas 2. http://en.wikipedia.org/wiki/Combined_diesel_and_gas 3. http://en.wikipedia.org/wiki/Combined_diesel-electric_and_gas 4. http://en.wikipedia.org/wiki/Combined_diesel_and_diesel 5. http://en.wikipedia.org/wiki/Combined_steam_and_gas 6. http://en.wikipedia.org/wiki/Combined_gas_or_gas 7. http://en.wikipedia.org/wiki/Combined_gas_and_gas 8. http://en.wikipedia.org/wiki/Combined_gas_and_steam 9. http://en.wikipedia.org/wiki/Combined_nuclear_and_steam_propulsion

Author : seaman(MKT)_DSTA_9 intake_ http://www.myanmarengineer.org/

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