YF-75D

The YF-75D is a liquid cryogenic rocket engine burning liquid hydrogen and liquid oxygen in a closed circuit expander cycle. It is China's third generation of upper stage cryogenic propellant engine, after the YF-73 and the YF-75. It is used in a dual engine mount in the H5-2 second stage of the Long March 5 launch vehicles. Within the mount, each engine can gimbal individually to enable thrust vectoring control.[1][3] As its predecessor, the YF-75 it can adjust its mixture ratio to optimize propellant consumption. But as an additional improvement, it can do multiple restarts, against the single one of its predecessor.[1]

YF-75D
Country of origin People's Republic of China
First flightLong March 5 inaugural flight (2016-11-03)
ManufacturerAcademy of Aerospace Liquid Propulsion Technology
Associated L/VLong March 5
PredecessorYF-75
StatusIn service
Liquid-fuel engine
PropellantLiquid oxygen / Liquid hydrogen
Mixture ratio6.0 (adjustable)
CycleExpander Cycle
Configuration
Chamber1
Nozzle ratio80
Performance
Thrust (vac.)88.26 kilonewtons (19,840 lbf)
Chamber pressure4.1 MPa (590 psi)
Isp (vac.)442 seconds (4.33 km/s)
Burn time780 seconds (13.0 min)
Used in
Long March 5 H5-2 second stage.
References
References[1][2]

The combustion chamber required a redesign to keep the power balance. Since the expander cycle uses the heat extracted from the cooling circuits to drive the turbines, the chamber had to be lengthened and the cooling passages redesigned. The engine uses a redesigned hydrogen turbine. It uses an axial two-staged low pressure ratio subsonic turbine that operates at 65,000rpm, which is between the second and third critical speed. It rests on dual elastic support dampers around the ceramic ball bearings.[1]

References
  1. Nan, Zhang (2013-09-23). "The Development of LOX/LH2 Engine in China" (pdf). 64rd International Astronautical Congress, Beijing, China. International Astronautical Federation. IAC-13-C4.1 (1x18525): 5. Retrieved 2015-07-08.
  2. ZHOU Limin, LIU Zhongxiang (2016). "Development, application, and prospect of expander cycle engine technology". JOURNAL OF ROCKET PROPULSION.
  3. "Chang Zheng-5 (Long March-5)". SinoDefence. Archived from the original on 2015-07-03. Retrieved 2015-07-08.


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