Combined gas and steam 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 electric powerplants built using this combined cycle can reach conversion efficiencies of over 60%. If the turbines do not drive a propeller shafts directly and instead a turbo-electric transmission is used, the system is 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 on diesel engines. COGAS should not be confused with Combined steam and gas power plants, which employ traditional, oil-fired boilers for steam turbine propulsion for normal cruising, 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 engines, e.g. in COGOG or COGAG mode, such as the Arleigh Burke-class destroyers, but 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 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, input into the crankshaft. Cogeneration Combined cycle Gizmag article discussing BMW's turbosteamer Article on BMW's alternative Combined Cycle Hybrid technology
Rev Prof James Williamson DD FRSE was a Scottish minister and mathematician, joint founder of the Royal Society of Edinburgh He was born in Dumfriesshire in 1725 the son of James Williamson of Tynron. He studied Mathematics at Glasgow University under Robert Simson, his theological training is unclear but he was licensed to preach by the Church of Scotland in 1752. He was ordained at Wamphray church in 1755 and translated to Closeburn in 1757. In 1761 he was appointed Professor of Mathematics at Glasgow University in succession to his mentor Prof Simson. In 1783 he was one of the founders of the Royal Society of Edinburgh, he appointed Prof James Millar as his successor. He died in his college house in Glasgow on 3 June 1795