YF rocket engines

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YF-24B; Four YF-23B type vernier nozzles for steering

The YF rocket engines ( Chinese  YF 系列 火箭 發動機  /  YF 系列 火箭 发动机 , Pinyin YF Xìliè Huǒjiàn Fādòngjī ) are a series of liquid rocket engines for medium-range missiles and civilian launch vehicles manufactured by the Chinese Academy for Liquid Rocket Engine Technology and its subsidiaries . As far as the engines work with cryogenic fuels, they are manufactured in Beijing . All other YF engines - operated with hypergolic fuel mixtures that can be stored at room temperature or with kerosene and liquid oxygen - are built in Xi'an . The engine tests take place in remote valleys of the Qinling Mountains .

Important engines

YF-1

Sidestream process

The first engine in the series was the “liquid rocket engine 1” (液体 火箭 发动机, Pinyin Yètǐ Huǒjiàn Fādòngjī , hence “YF-1” for short) for the first stage of the medium-range missile Dongfeng 3 . It was developed on Base 067, founded in 1965 in Baoji, Shaanxi Province . The bypass flow engine, four of which were combined in a 1180 kg module called "YF-2", used 1,1-dimethylhydrazine , also known as "UDMH", with the oxidizers nitric acid (73%) and nitrous tetroxide (27%), also known as "AK-27", as a fuel. With a mixing ratio of oxidizer to fuel of 2.46, it generated a thrust of 255 kN at sea level - i.e. 1020 kN starting thrust for the rocket - and delivered a specific impulse of 240 s. The same engine was used in the first stage of the Changzheng 1 civilian rocket . The YF-3 engine developed for the second stage of Dongfeng 3 and Changzheng 1 was significantly more powerful. This engine, of which only one was used in the stage, generated a vacuum thrust of 320 kN with AK-27 and UDMH in a mixing ratio of 2.48 and delivered a specific impulse of 287 s.

These basic engines have been further improved over time. For example, with the YF-1A, which generated a thrust of 275 kN and a specific impulse of 243 s, the maximum range of the Dongfeng 3A, which was first launched in 1985, could be increased from 2660 km to 2810 km. The same engine or the four-engine module YF-2A was used in the Changzheng 1D, which took off for the first time in 1995 for a suborbital test flight. Together with a fuel change in the YF-3 second stage engine, the payload of the rocket could be increased from 300 to 740 kg.

YF-20

In autumn 1969, the 2nd office for mechanical engineering and electrical engineering in Shanghai (today Shanghai Academy for Space Technology ) began developing the two-stage launch vehicle Feng Bao 1 . From 1970, the 1st Academy of the Seventh Ministry of Mechanical Engineering (第七 机械 工业 部 第一 研究院, today China Academy of Launch Vehicle Technology ) under Ren Xinmin worked on a similar launch vehicle with the designation based on the Dongfeng 5 ICBM " Changzheng 2 ", later called "Changzheng 2A". For these two rockets, the base 067 developed the YF-20 engine, which also works according to the bypass flow method. Unlike the YF-1, the engines in this series, which are still in use today, use pure dinitrogen tetroxide as an oxidizer. The fuel remained unchanged with 1,1-dimethylhydrazine . A YF-20 produced a thrust of 696.25 kN and a specific impulse of 259 s. For the first stage of the FB-1 and the CZ-2, four of these engines were combined in a "YF-21" module that weighs 2850 kg. These rockets achieved a launch thrust of 2,785 kN, more than twice as much as the YF-1 propulsion system. For the second stage of Feng Bao 1, the YF-22 was developed with a nozzle optimized for operation in a vacuum . This engine generated a vacuum thrust of 719.8 kN and a specific impulse of 289 s.

In the Changzheng 2, the second stage was steerable. For this purpose, four pivoting YF-23 vernier nozzles were attached around the YF-22 engine . These are small engines with a vacuum thrust of 46.1 kN each, which, like the main engine, use the hypergolic fuel mixture UDMH / nitrous tetroxide. The drive unit consisting of the YF-22 and four YF-23 vernier nozzles is known as the "YF-24". Like the other engines of the YF-20 series, the YF-24 is still used in an improved form, for example as the YF-24B in the Changzheng 2C or as the YF-24D in the second stage of the Changzheng 3B .

YF-75

The engines, which operate with hypergolic fuel mixtures that can be stored at room temperature , were mainly developed on the basis of 067 in Shaanxi. At the same time, however, at the suggestion of Qian Xuesen , then deputy head of the 5th Research Institute , work in Beijing began in January 1961 on engines that used the cryogenic fuel combination of liquid hydrogen / liquid oxygen . This allows a higher specific impulse than UDMH / nitrous tetroxide and is far less toxic. In cooperation with what was then the Research Institute for Mechanics of the Chinese Academy of Sciences , a combustion chamber was designed and built in March 1965 which, although using gaseous hydrogen, generated a thrust of 2 kN as an oxidizer and was successfully ignited several times. In 1970, despite the Cultural Revolution and tensions with the Soviet Union, a combustion chamber for liquid hydrogen and oxygen was constructed that generated a thrust of 8 kN. Today this is considered a breakthrough in the development of the Chinese LOX / LH 2 engines.

4 × YF-73 module

In October 1970, when Ren Xinmin had just started developing the Changzheng 2 launch vehicle, which was still working with UDMH / nitrous tetroxide, he commissioned the Beijing Research Institute for Space Propulsion to develop a prototype of a cryogenic engine with a thrust of around 40 kN. A good four years later, the said prototype, which worked according to the sidestream method, was ready; on January 25, 1975 it ran for the first time for 20 seconds on the test bench. On March 31, 1975, Mao Zedong approved the plan to launch a geostationary communications satellite , later called Dong Fang Hong 2 , into a 36,000 km high orbit; a project commonly known as " Project 331 " after the date . This required a three-stage rocket, the Changzheng 3 . The first two stages of the new rocket, including the YF-20 series engines, were carried over from the Changzheng 2. For the third stage, however, the YF-73 has now been developed in Beijing. This engine weighed 236 kg and, with an oxygen-to-hydrogen ratio of 5.0, generated a thrust of just over 11 kN with a specific impulse of 420 s, 45% more than the YF-22. Here, too, four engines were combined into one drive module. Reignited and individually pivotable about an axis, they together generate a vacuum thrust of 44.15 kN.

The YF-73 had its first use on January 29, 1984 in the - unsuccessful - attempt to place the communications satellite Dong Fang Hong 2-1 into geostationary orbit. The engine was used on a total of 13 flights. Three of them failed (1984, 1991, 1996), each of which was due to a failure of the YF-73, in two cases (1984 and 1991) a few seconds after its second ignition. After a last flight on June 25, 2000, the engine was decommissioned due to its lack of reliability and the desire for an even more powerful drive.

As early as 1982, when the problems with the YF-73 were not yet known, engineers at the Beijing Research Institute for Space Propulsion had started developing a successor model for higher payloads. The engine, named "YF-75", was intended for use in the third stage of the improved Changzheng 3A launcher . In view of the increasingly demanding communication satellites, the transport capacity for geostationary orbits should be increased from 1.5 t to 2.6 t. After the Chinese government had given permission in October 1985 to offer commercial satellite launches with launch vehicles of the type Changzheng 2 and Changzheng 3 on the international market, development work intensified.

The YF-75 also works according to the bypass flow method (see the illustration above); its fuel pumps are driven by hot exhaust gas that is generated in a separate small combustion chamber, the pre-burner. Unlike all previous engines from the same manufacturer, the YF-75 uses two turbines to drive the hydrogen and oxygen pumps, so that both can work at different, optimal speeds. The faster of the two, the hydrogen pump, rotates at 42,000 revolutions per minute . For installation in the rocket, two of the engines, each generating 78.45 kN of vacuum thrust, are combined in one module, where they give the rocket stage a thrust of 156.9 kN. The specific impulse of this drive is 437 s. The pumps are permanently mounted on the combustion chambers, which can be swiveled around two axes for vector control .

This concept proved extremely successful. From February 8, 1994 to March 9, 2020, a total of 110 flights were carried out with rockets of the type Changzheng 3A, 3B and 3C, in the third stage of which the engine is installed. Only in one of them, the launch of the Indonesian communications satellite Palapa-D on August 31, 2009, did one of the YF-75 engines malfunction after the second ignition. As a result, the satellite was placed in an orbit that was too low. It was not until April 9, 2020 that a new 3rd stage malfunction occurred when a Changzheng 3B was launched, which was supposed to put an Indonesian communications satellite back into orbit.

The next start of a Changzheng 3B was scheduled for the morning of June 16, 2020. During the countdown, just after 8 p.m. the previous day, the engineers noticed abnormal pressures on the pressure reducing valve in the oxygen line of one of the two engines in the third stage propulsion module. First of all, it was decided to replace the valve with a replacement valve available on site. When removing the valve, however, the technicians noticed an approximately three to four centimeters long, chicken's foot-shaped hairline crack in the housing of the valve. The Beijing Academy for Launch Vehicle Technology, which was quickly contacted, carried out a thorough test on a randomly selected valve from the same production lot and again discovered a hairline crack. Wu Yansheng, chairman of the board of directors of China Aerospace Science and Technology Corporation , suggested that the launch be postponed, a decision that the commander of the People's Liberation Army in charge of the mission fully supported. A flawless replacement valve brought in from Beijing was installed two days later, and on June 23, 2020, the missile for the Strategic Combat Support Force of the People's Republic of China transported the last of its Beidou navigation satellites into a geostationary orbit.

YF-75D

Expander process

Since May 2001 the China Aerospace Science and Technology Corporation had been working intensively on a modular, heavy launch vehicle . In August 2006 this concept was approved by the State Council of the People's Republic of China ; later it became known as "Changzheng 5". For the second stage of the larger variants of this rocket family, a hydrogen / oxygen drive with two "YF-75D" engines was provided, a further development of the YF-75. The system of two separate turbo pumps for hydrogen and oxygen was adopted, which are no longer operated with hot gas from a pre- burner , but work according to the expander process : the hydrogen is pumped through the wall of the combustion chamber, where it evaporates and at the same time cools the chamber . From there it is passed through the turbines of the fuel pumps and drives them before it reaches the combustion chamber. In order to ensure the desired heating of the hydrogen, the combustion chamber had to be significantly lengthened compared to the YF-75 - it is about twice as long on the YF-75D. On the other hand, the pre-burner was saved, which makes the engine more reliable and shortens the development time.

While the YF-75 uses turbines with a radial flow direction (the water mill principle), the axial design was selected for the YF-75D after tests with both turbine types. The hydrogen pump rotates at 65,000 rpm. The mixing ratio of oxygen to hydrogen is approximately 6.0 and can be adjusted via a valve in the oxygen line. Unlike the YF-75, the YF-75D can be ignited more than twice. Two of these engines are combined into a module and individually gimbaled . The YF-75D generates a specific impulse of 442 s and a vacuum thrust of 88.26 kN, giving the second stage of the Changzheng 5 a total thrust of 176.52 kN.

YF-77

As early as January 2002, the National Defense Commission for Science, Technology and Industry had given approval to develop a powerful hydrogen / oxygen engine for the first stage of the Changzheng 5 . Since sophisticated software was already available at this time to support the engineers in the calculations with computer simulations, a first draft was submitted in mid-2002. The bypass flow process was chosen as the working principle as with the YF-75, again with a common pre-burner but two separate turbo pumps for hydrogen and oxygen. In contrast to the YF-75, where the hot gas is released into space via a common pipe after passing through the two turbines, each turbine on the “YF-77” engine has its own exhaust pipe. Two of these engines with a lower nozzle diameter of 1.45 m are individually deflectable suspended in a frame and together with this form a 4.2 m high and 2.7 t heavy drive module. The YF-77 achieves a thrust of 510 kN at sea level with a specific impulse of 438 s.

The most demanding components in an engine are the turbo pumps, which are therefore particularly carefully designed and extensively tested. The turbines that drive the centrifugal pumps for hydrogen (35,000 rpm) and oxygen (18,000 rpm) in the YF-77 each consist of two stages, with the actual impeller and an outlet stator , which removes the rotational swirl of the hot gas flowing out so that it flows out more uniformly can. Most parts of the turbine are made of the nickel-based superalloy In 718 from the American Special Metals Corporation . This material retains its strength over a wide temperature range and is therefore particularly suitable for applications in engine construction. On the other hand, it is very difficult to work with. Therefore, stainless steel was chosen as the material for the outlet stator.

This austerity measure turned out to be a fatal mistake. When the Changzheng 5 was launched for the second time on July 2, 2017, the high temperature of the exhaust gas flow caused a problem in one of the engines in the exit area of ​​one of the turbines, which led to a loss of thrust 346 seconds after launch and the rocket to crash. Troubleshooting, redesign of the turbine - the material for the outlet stator was changed to In 718 and five more stator blades were added in the turbine - tests and new redesigns took a total of two years. The next launch of the rocket did not take place until December 27, 2019, exactly 908 days after the crash. As a result, among other things, the start date of the Chang'e-5 lunar probe, originally scheduled for the end of 2019, was postponed to the end of 2020. The construction of the modular space station was also delayed.

YF-100

YF-100

In connection with the project discussed at the time for the development of a heavy launch vehicle (today's Changzheng 5), the Xi'an research institute for space propulsion began work on the high-performance YF-100 engine in early 2000. The YF-100 was to work according to the main flow method and run on a diergolen fuel combination of rocket kerosene and liquid oxygen . At sea level it should deliver a thrust of 1200 kN.

With this new development one had to contend with great difficulties: of the first four engines produced, two exploded on the test bench, two caught fire. It took almost half a year for the engineers to find the cause of the malfunction. Using computer simulation, they worked out an improved ignition sequence for the engine, and from then on it ran flawlessly. On October 30, 2005, the first 300-second long-term test of a prototype took place on the test bench for deflectable engines at the Xi'an Space Propulsion Testing Institute in Feng County. The burning time of 173 seconds planned for regular use in the Changzheng boosters was thus significantly exceeded. The test was attended by Zhang Yunchuan (张云川, * 1946), the head of the Science, Technology and Industry Commission for National Defense , as well as Chen Deming (陈德铭, * 1949), Governor of Shaanxi Province, and other prominent figures.

After the Xi'an research institute had produced a total of 61 examples of the engine and tested it in a wide variety of ways, the YF-100 was approved on May 28, 2012 by the national authority for science, technology and industry in the national defense . In contrast to the engines of the 70 series, the YF-100 has only one turbine that drives both the oxygen and the kerosene pump via a common axis; the control of the fuel mixture (2.7 ± 10%) takes place solely via valves. The thrust vector is also controlled differently than usual. Originally, the plan was to mount the pre-burner and turbo pump firmly on the combustion chamber and to pivot the entire engine. In order to reduce the rest mass to be moved, however, this was changed to a post-pump pivoting as in the adjacent picture, where the hydraulic cylinders operated with kerosene as hydraulic fluid attach to the upper edge of the nozzle and deflect it by up to 8 ° from the vertical. In the boosters of the Changzheng 5 and Changzheng 7 , the engine can only be pivoted around one axis, when used in the core stage of the Changzheng 7 around two axes.

The nozzle of the YF-100 has a diameter of 1.34 m at the bottom. At sea level, the engine generates a thrust of 1224 kN and delivers a specific pulse of 300 s. For use in the second stage of the Changzheng 6 and Changzheng 7 there is a smaller version, the YF-115, with a nozzle diameter of 97 cm, a vacuum thrust of 180 kN and a specific impulse of 342 s. The YF-100K version was developed for the boosters of the new generation of manned rockets , which are scheduled to make their maiden flight in 2025.Template: future / in 5 years

LOX / methane engine

As an inexpensive alternative to hydrogen / oxygen engines, the Beijing Research Institute for Space Propulsion has been working for some time on a reusable engine that works according to the bypass flow process with a thrust of 600-700 kN at sea level, the liquid oxygen and methane in a mixing ratio of 2, 88 used as fuel. The combustion behavior of gaseous methane with liquid oxygen and liquid methane with liquid oxygen was studied in several experiments with scaled-down models and individual components. The first prototype of the engine ran from January 2011 in four tests for a total of 67 seconds. In September 2015, an improved version was started and switched off 13 times and ran for 2103 seconds.

Web links

Individual evidence

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