# Cheng cycle
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{{Short description|Thermodynamic cycle}}
{{thermodynamics|cTopic=Processes and Cycles}}
The '''Cheng cycle''' is a [thermodynamic cycle](/source/thermodynamic_cycle) which uses a combination of two working fluids, one gas and one steam. It can therefore be considered a combination of the [Brayton cycle](/source/Brayton_cycle) and the [Rankine cycle](/source/Rankine_cycle). It was named for Dr. Dah Yu Cheng.[Penning, F. M. and de Lange, F. M. (1995) Steam Injection: analysis of a typical application ''Applied Thermal Engineering'' Vol. 16, No. 2, pp. 115 125] The steam so produced is injected into the gas turbine's combustion chamber to increase power output.[De Paepe, M. and E. Dick (2001) Technological and economical analysis of water recovery in steam injected gas turbines, ''Applied Thermal Engineering'', Volume 21, Issue 2, January 2001, Pages 135–156] The process can be thought of as a parallel combination of the gas-turbine [Brayton cycle](/source/Brayton_cycle) and a steam-turbine [Rankine cycle](/source/Rankine_cycle).[Stadler, F. and U. Schneider, (1997) ELIN Cheng Cycle, Elin Energieversorgung GmbH, 1997][Motz, D.A. (1987) ''The Cheng Cycle: principles and applications, Ass. Energy Engng, 8th World Energy Engng Conf.'', Atlanta, USA] The cycle was invented by Prof. Dah Yu Cheng of the [University of Santa Clara](/source/University_of_Santa_Clara), who patented it in 1976.[[https://books.google.com/books?id=PKBKP6XWCq4C&dq=%22Cheng+cycle%22&pg=PA316 Cen, Ke-fa Yong Chi, Jianhua Yan (2007) ''Challenges of Power Engineering and Environment: Proceedings of the International Conference on Power Engineering'', Springer] (Accessed August 2012)][Cheng, D.Y. and A.L.C. Nelson (2002) ''Chronological development of the Cheng cycle steam injected gas turbine during the past 25 years''. in: Anon (Ed.), ''Proceedings of ASME Turbo Expo'' 2002, Amsterdam, ASME Paper No. GT-2002-30119 (2002), pp. 421–428]
A fully Cheng-cycle gas/steam two-fluid turbine can achieve a theoretical [thermal efficiency](/source/thermal_efficiency) of 60%, matching or even exceeding many traditional [combined-cycle gas turbines](/source/Combined_cycle_power_plant) that keep the steam [Rankine cycle](/source/Rankine_Cycle) and gas [Brayton cycle](/source/Brayton_Cycle) as separate loops.