Combined gas and steam (COGAS) is the name given to marine compound powerplants comprising

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

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 60%. If the turbines do not drive a

propeller shaft A drive shaft, driveshaft, driving shaft, tailshaft (Australian English), propeller shaft (prop shaft), or Cardan shaft (after Girolamo Cardano) is a component for transmitting mechanical power and torque and rotation, usually used to connect ...

s directly and instead a

turbo-electric A turbo-electric transmission uses electric generators to convert the mechanical energy of a turbine (steam or gas) into electric energy, which then powers electric motors and converts back into mechanical energy that power the driveshafts. Tu ...

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 Combined diesel and gas (CODAG) 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. Pioneered by Germany with the , a ...

systems when run solely on diesel engines. Especially COGAS should not be confused with

Combined steam and gas Combined steam and gas (COSAG) is a propulsion system for ships using a combination of steam turbines and gas turbines to power the shafts. A gearbox and clutches enable either of the engines or both of them together to drive the shaft. It has t ...

(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. COGAS has been proposed as upgrade for ships that use gas turbines as their main (or only) engines, e.g. in

COGOG Combined gas or gas (COGOG) 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 turb ...

COGAG Combined gas turbine and gas turbine (COGAG) is a type of propulsion system for ships using two gas turbines connected to a single propeller shaft. A gearbox and clutches allow either of the turbines to drive the shaft or both of them combined. ...

mode, such as the s, but currently no

naval ship A naval ship is a military ship (or sometimes boat, depending on classification) used by a navy. Naval ships are differentiated from civilian ships by construction and purpose. Generally, naval ships are Damage control, damage resilient a ...

uses this concept. However some modern

cruise ship Cruise ships are large passenger ships used mainly for vacationing. Unlike ocean liners, which are used for transport, cruise ships typically embark on round-trip voyages to various ports-of-call, where passengers may go on tours known as ...

s are equipped with COGES. E.g. Celebrity Cruises' ''

Millennium A millennium (plural millennia or millenniums) is a period of one thousand years, sometimes called a kiloannum (ka), or kiloyear (ky). Normally, the word is used specifically for periods of a thousand years that begin at the starting point (ini ...

'' and other ships of her class use turbo-electric plants with two

General Electric LM2500 The General Electric LM2500 is an industrial and marine gas turbine produced by GE Aviation. The LM2500 is a derivative of the General Electric CF6 aircraft engine. As of 2004, the U.S. Navy and at least 29 other navies had used a total of more ...

+ gas turbines and one steam-turbine. BMW is currently researching combined gas and steam for automotive use, using their

turbosteamer A turbosteamer is a term used by BMW to describe a combined cycle engine. Waste heat energy from the internal combustion engine would be used to generate steam (see Waste Heat Recovery Unit) for a steam engine which would create supplemental po ...

system. This uses the

waste heat Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility ...

of combustion from the exhaust and turns it into steam to produce torque which is input into the crankshaft.

References

External links

Gizmag article discussing BMW's turbosteamerArticle on BMW's alternative Combined Cycle Hybrid technology
{{DEFAULTSORT:Combined Gas And Steam Marine propulsion Steam power de:Gas-und-Dampf-Kombikraftwerk

See also

References

External links