(1) Basic information
YF-73 is the first hydrogen-oxygen engine designed by my country. It adopts a single-pump four-chamber design and is installed on the third stage of the Long March-3 launch vehicle. In March 1975, my country launched the “331 Project” to develop the first hydrogen-oxygen engine, code-named YF-73, and thus began the development of YF-73. On May 26, 2000, the YF-73 was retired due to low engine reliability and low rocket carrying capacity. During its service, the YF-73 flew a total of 13 missions, of which 3 failed and 10 were successful.
(2) Technical parameters
YF-73 uses a pump-pressure gas generator cycle and a single turbine gearbox for power transmission. One turbine pump supplies propellant to four thrust chambers. The thrust chambers are cooled by liquid hydrogen and can swing in one direction of ±24° around its axis of rotation to provide attitude control torque. YF-73 has a rated vacuum thrust of 4 t and has the ability to start up twice. The specific technical parameters are as shown in the table below.
1.Basic parameters
length
diameter
quality
fuel
oxidizing agent
Mixing ratio
combustion chamber
Number of turbine pump rotors
Nozzle area ratio
1438 mm
2220 mm
245 kg
liquid hydrogen
liquid oxygen
5.0
4
1
40
2.Performance parameters
thrust
(vacuum)
specific impulse
(vacuum)
combustion chamber
pressure
fuel flow
Oxidant flow
44.43 kN
4119 m/s
2.63 MPa
1.78 kg/s
9.0 kg/s
(3) System composition
YF-73 is composed of 8 main parts, including the cylinder starting system, main system (thrust chamber propellant supply system), auxiliary system (turbine fluid supply system), ignition system, purge system, pre-cooling system, tank pressurization system and pneumatic control system.
1. Start the system
Including nitrogen bottles, electric gas valves, manual switches, etc.
2. Main system
Including pump front valve, turbine pump, main valve, throttle ring, thrust chamber, pipeline, etc.
3. Vice system
Including gas generator, auxiliary system control valve, oxidant regulator, cavitation venturi, pipeline, etc.
4. Ignition system
Powder igniter: ignition energy source for combustion chambers and gas generators.
5. Blow-off system
Including electric air valves, pressure reducers, one-way valves, etc.
6. Pre-cooling system
Including pre-cooling relief valve and corresponding pipelines, etc.
7. Tank pressurization system
Including heat exchangers, cavitation venturis that control boost flow, etc.
8.Pneumatic control system
Including pressure reducer, pneumatic valve, electric air valve, etc.
(4) Composition of components
1. Thrust chamber
1.1 Composition
The thrust chamber consists of the injector, combustion chamber and nozzle. The injector adopts a flat-top structure with two chambers composed of three bottoms. The oxidizer chamber is on the top and the fuel chamber is on the bottom. There is a four-hole seat in the center of the injector for installing the gunpowder igniter. In addition, the injector is equipped with a coaxial two-component nozzle, arranged in concentric circles. Each dual-component nozzle is composed of an oxidizer nozzle in the middle and an annular gap hydrogen gas nozzle on the outside.
1.2 Process
The combustion chamber and nozzle are formed by brazing the inner and outer walls. The nozzle profile is designed according to Roche’s best thrust nozzle. There are grooved cooling channels milled on the inner wall. The coolant is introduced into the cooling channel from the expansion ratio of 15:1, first flows to the nozzle, and then returns to the injector through the adjacent groove. A transmission shaft is welded to the body of the combustion chamber, and one end of the shaft engages with the servo mechanism to achieve one-way swing of the thrust chamber.
1.3 Materials
The injector panel is made of porous material and is sweat-cooled with liquid hydrogen.
2. Turbo pump
2.1 Composition
The turbopump consists of a turbine, a fuel pump, an oxidizer pump and a gearbox. The turbine and the liquid hydrogen pump are coaxial and are the driving shaft; the liquid oxygen pump has a separate shaft and is the driven shaft; the middle is driven by a reduction gear.
The turbine is a single-stage impact structure, consisting of a turbine cover, a rotor and a main shaft.
The fuel pump consists of an inducer, a centrifugal wheel, a spiral shell, and front and rear sealing rings.
The oxidant pump consists of an inlet pipe, a pump shaft, an inducer, a centrifugal wheel, front and rear sealing rings and a pump housing.
The function of the gearbox is to transmit the power required by the oxidant pump. The gears are cooled by hydrogen, and their cooling flow is controlled by three restrictors.
In addition, there are 6 end face seals and 6 sets of low-temperature bearings on the entire turbine pump. To dampen vibrations, bushing-type elastic supports are applied to the main shaft pivot point at the turbine end.
2.2 Materials
The turbine cover, restrictor, end-face seal and static ring components are made of stainless steel; the turbine rotor, main shaft, etc. are made of high-temperature alloy; the two pump housings, gearbox, centrifugal wheel, inducer, etc. are made of aluminum alloy.
2.3 Performance parameters
2.3.1 Turbine
inlet pressure
outlet pressure
flow
Speed
1.36 MPa
0.273 MPa
0.3 kg/s
36960 r/min
2.3.2 Fuel pump
inlet pressure
outlet pressure
flow
efficiency
0.245 MPa
4.36 MPa
1.817 kg/s
0.547
2.3.3 Oxidant pump
inlet pressure
outlet pressure
flow
efficiency
0.294 MPa
4.7 MPa
9.086 kg/s
0.703
3.Gas generator
3.1 Composition
The gas generator injector has a flat-top structure with three layers of flat bottom. The fuel chamber is between the inner bottom and the midsole, and the oxidizer chamber is between the outer bottom and the midsole. The center of the injector is the gunpowder igniter nozzle, which is surrounded by coaxial dual-component nozzles arranged into two concentric circles, and there are cooling holes on the outermost side. The body is composed of a cylindrical section and a tapered convergence section. Both the cylindrical section and the convergence section are double-walled structures, with grooves milled on the inner wall to form a regeneration cooling channel.
3.2 Performance parameters
gas pressure
Oxidant flow
fuel flow
Mixing ratio
1.48 MPa
0.142 kg/s
0.158 kg/s
0.9
4.Valve
4.1 Fuel pump front valve
4.1.1Type
The front valve of the fuel pump is a ball valve structure.
4.1.2 Location
The fuel pump front valve is located at the upper end of the fuel pump inlet pipe.
4.1.3 Function
Used to connect or cut off the propellant supply from the fuel tank to the engine.
4.2 Oxidant pump front valve
4.2.1Type
The front valve of the oxidant pump is a ball valve structure.
4.2.2 Location
The front valve of the oxidizer pump is located at the upper end of the inlet pipe of the oxidizer pump.
4.2.3 Function
Used to connect or cut off the propellant supply from the oxidizer tank to the engine.
4.3 Fuel main valve
4.3.1 Type
The main fuel valve is a mushroom valve directly controlled by a bellows.
4.3.2 Location
The fuel main valve is located on the main system line after the fuel pump.
4.3.3 Function
Used to control the supply of liquid hydrogen to the combustion chamber.
4.4 Oxidizer main valve
4.4.1 Type
The oxidizer main valve is a mushroom valve directly controlled by a bellows.
4.4.2 Location
The oxidizer main valve is located on the main system pipeline after the oxidizer pump.
4.4.3 Function
Used to control the supply of liquid oxygen to the combustion chamber.
4.5 Fuel (oxidant) subsystem control valve
4.5.1Type
The fuel (oxidant) subsystem control valve is a two-way mushroom valve.
4.5.2 Location
The fuel (oxidant) subsystem control valve is located at the inlet of the fuel (oxidant) chamber of the gas generator injector.
4.5.3 Function
When the gas generator is not working, the fuel (oxidant) flowing through the auxiliary system is discharged from the discharge port of the valve; when the gas generator is working, the discharge port is closed and the channel into the gas generator is opened, allowing the fuel (oxidant) to enter the fuel (oxidant) cavity of the injector.
4.6 Fuel (oxidizer) drain valve
4.6.1Type
The fuel (oxidant) drain valve is a normally closed mushroom valve.
4.6.2 Function
When the engine is purging and precooling, the valve is ventilated and opened to release the purge gas and precooling propellant. When the main stage is working, the valve is closed; when shutting down, the valve is opened to relieve pressure and prevent water hammer.
(5) Working process
The YF-73 uses high-pressure nitrogen to start, and a powder igniter is used to ignite the thrust chamber and gas generator.
1. Before starting
Before starting the engine, open the pre-pump valves of the oxidizer pump and the fuel pump. Liquid oxygen and liquid hydrogen flow into the front of the two main valves of the engine under the boost pressure of the tank, and pre-cool the components and conduits that contact the propellant in front of the two main valves.
2.At startup
When the engine is started, power is turned on to open the electric valve of the starting cylinder, and the high-pressure nitrogen in the starting cylinder blows the turbine, causing the turbine pump to start working. Under the pressure behind the pump, the main valve of the oxidizer opens, and liquid oxygen begins to fill the oxidizer chamber of the injector. After a certain time interval, the oxidant subsystem control valve opens, and liquid oxygen begins to fill the oxidizer chamber of the gas generator injector. At this time, the gunpowder igniter of the gas generator is powered on for ignition, and then the fuel subsystem control valve opens, and liquid hydrogen (from the fuel subsystem pipeline and the bypass system) enters the fuel chamber of the gas generator injector. Under the ignition of the gunpowder igniter, the hydrogen and oxygen injected into the gas generator are mixed and burned to produce high-temperature gas to drive the turbine.
At the same time that the fuel auxiliary system control valve opens, the fuel main valve opens under the action of pressure behind the pump, and liquid hydrogen begins to fill the combustion chamber. At the same time, the gunpowder igniter in the combustion chamber is energized and ignited, and the combustion chamber begins to build pressure.
Then, close the fuel and oxidizer drain valves according to the program, and turn off the power and close the electric gas valve of the starting gas cylinder. The gas generator and the powder igniter in the combustion chamber were also powered off at the same time. After a certain time interval, the valve on the fuel subsystem bypass line is also closed.
At this time, the engine ends the starting process and enters the main stage steady state operation.
3. Shut down for the first time
When the engine’s first main stage work ends, the relevant valves are closed or opened according to the shutdown command of the rocket control system according to the program, and the helium gas provided by the gas cylinder on the arrow blows out the gas generator injector oxidizer chamber system and the combustion chamber oxidizer system. At this time, the engine enters the taxiing stage. During the coasting phase the two pump front valves do not close.
4.Second startup
Before the engine is started for the second time, the two drain valves are opened to pre-cool the engine for the second time. When the engine is started for the second time, stop blowing the oxidizer cavity of the gas generator and combustion chamber. At this time, power is turned on to open another starting cylinder, and the high-pressure nitrogen blows the turbine, causing the turbine pump to start working. The rest of the working process is the same as the first startup.
The specific working process can be deduced according to the figure below.
(6) Development history
Preliminary research work on my country’s liquid hydrogen/liquid oxygen engine officially began in 1970. In 1976, after the third stage of Long March 3 decided to use liquid hydrogen and liquid oxygen as propellants, Chinese researchers started the design work of YF-73 and the production of experimental products based on the original preliminary research. In 1978, my country began engine hot testing of the YF-73; in 1980, the YF-73 passed the 800-second long-range, high-thrust and second-start test; in 1982, the Long March 3 third-stage full system test was successfully conducted; in the second quarter of 1983, the YF-73 flight test products were successfully delivered.
Due to my country’s lack of sufficient understanding of the physical properties of liquid hydrogen and liquid oxygen under high vacuum and low gravity field conditions, in February 1984, when the YF-73 participated in the first flight test of the Long March 3, the second engine ignition failed. Chinese researchers conducted an in-depth and detailed analysis of the flight process based on the information provided by telemetry parameters. After seventy days of hard work by scientific researchers, the engine system was improved and a hot test was conducted. On April 8, 1984, Long March 3 successfully sent my country’s communications satellite into the geosynchronous transfer orbit for the first time, and the performance of YF-73 was verified by flight.
(7) Evaluation
As my country’s first hydrogen-oxygen engine, YF-73 has shortcomings in performance and cycle methods, but its development process has accumulated valuable experience and laid the foundation for the subsequent development of hydrogen-oxygen engines. Generally speaking, the historical significance of the YF-73 is greater than its technological advancement. It is an important transition model for my country from “following” to “running alongside” an international aerospace power.
