View source for Combined gas and steam

{{Short description|Marine propulsion system}}
{{details|Combined cycle}}
'''Combined gas and steam''' ('''COGAS''') is a type of [[marine propulsion]] system comprising [[Gas turbine|gas]] and [[Steam turbine|steam]] turbines, the latter being driven by steam generated using the heat from the exhaust of the gas turbines.

==System==
{{combined-marine-propulsion}}
In this way, some of the otherwise lost energy can be reclaimed and the [[specific fuel consumption (shaft engine)|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 %.<ref>{{cite web|url=https://www.ge.com/power/about/insights/articles/2018/03/nishi-nagoya-efficiency-record |title=World's Most Efficient Combined-Cycle Power Plant|publisher= GE Power |access-date=2018-06-17}}</ref>

[[Image:COGES diagram.svg|thumb|A COGES system:{{ordered list|Electric generators|Steam turbine|Condenser|Pump|Boiler / heat exchanger|Gas turbine}}]]
If the turbines do not drive a [[propeller shaft]] directly and instead a [[turbine–electric transmission]] is used, the system is known as '''COGES''' (combined gas–electric and steam).

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]] (CODAG) systems when run solely on diesel engines. Especially COGAS should not be confused with [[combined steam and gas]] (COSAG) powerplants, 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 [[Combined gas or gas|COGOG]] or [[Combined gas and gas|COGAG]] mode, such as the {{sclass|Arleigh Burke|destroyer|1}}s, but currently no [[naval ship]] uses this concept. However some modern [[cruise ship]]s  are equipped with COGES. E.g. the [[Celebrity Cruises]]' {{sclass|Millennium|cruise ship|4}} use turbine–electric powerplants with two [[General Electric LM2500+]] gas turbines and one steam turbine.

[[BMW]] is currently{{when|date=January 2024}} 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]].{{cn|date=September 2022}}

==See also==
*[[Cogeneration]]
*[[Combined cycle]]
*[[Combined cycle powered railway locomotive]]

==References==
{{Reflist}}

==External links==
*[http://www.gizmag.com/go/4936/ Gizmag article discussing BMW's turbosteamer]
*[https://paultan.org/2008/06/09/bmw-continues-exhaust-gas-heat-energy-recovery-research/ Article on BMW's alternative Combined Cycle Hybrid technology]

{{DEFAULTSORT:Combined Gas And Steam}}
[[Category:Marine propulsion]]
[[Category:Steam power]]
[[Category:Turbo generators]]

[[de:Gas-und-Dampf-Kombikraftwerk]]