CE20 Cryogenic Engine: ISRO’s Propulsion Technology

1. The Indian Space Research Organisation's (ISRO) CE20 cryogenic engine has passed a critical sea-level test, marking a significant breakthrough in its propulsion technology.
2. This advancement is crucial as ISRO prepares for its Gaganyaan mission, India's first manned spaceflight.

Key Highlights of the Test:

1. The test was conducted at the ISRO Propulsion Complex in Mahendragiri, Tamil Nadu.
2. A key innovation introduced in the sea-level test was the "Nozzle Protection System."
3. This system is designed to manage issues such as flow separation within the nozzle, which can cause vibrations, thermal problems, and potential damage.
4. The engine’s design also addressed challenges related to engine restart capability.
5. In 2023, Hindustan Aeronautics Limited (HAL) set up the Integrated Cryogenic Engine Manufacturing Facility in Bengaluru.

How Does a Cryogenic Engine Work?

A cryogenic engine generates thrust through an internal combustion process, relying on the principle of Newton's Third Law of Motion: "Every action has an equal and opposite reaction." This is achieved by using cryogenic propellants (fuel and oxidizer) that are stored at extremely low temperatures.

• Cryogenic Propellants: These engines use liquefied gases that are kept at very low temperatures. The common cryogenic fuels are:
  • Fuel: Liquid hydrogen (LH2) is used, which is liquefied at a temperature of -253°C.
  • Oxidizer: Liquid oxygen (LOX) is used, liquefied at -183°C.

Note: A semi-cryogenic engine uses refined kerosene instead of liquid hydrogen. This offers advantages such as lighter weight and storage at normal temperatures.

Advantages of Cryogenic Engines:

1. Efficiency and Thrust:

1. Cryogenic propulsion offers superior thrust compared to solid and earth-storable liquid propellants.
2. The combination of LOX and LH2 produces maximum energy and light water vapor, resulting in higher performance.

2. Fuel Efficiency:

1. Cryogenic engines use less fuel than other systems.
2. For instance, ISRO's PSLV Vikas engine burns 3.4 kg of fuel per second, while a cryogenic engine needs only 2 kg/sec for the same thrust.
3. The specific impulse (efficiency) of cryogenic engines is about 450 seconds, compared to 260 seconds for solid propellants.

3. Eco-Friendly Technology: The combustion of hydrogen and oxygen produces only water vapor, making cryogenic propulsion a clean, carbon-free solution.

4. Capability for Heavy Payloads and Long Missions: The high efficiency of cryogenic engines makes them ideal for heavy payloads and long-duration space missions, such as ISRO’s Gaganyaan and Chandrayaan missions.

Challenges in Cryogenic Engine Technology:

1. Complex Technology: Cryogenic engines are more complex than solid or liquid propellant systems due to the use of extremely low-temperature propellants and the thermal and structural challenges they present.
2. Thermal Issues: High thermal gradients and stresses can lead to issues such as cracks in the divergent outer shell, nozzle distortions, and blockages in coolant channels.
3. High Operational Pressures: The high pressures in the thrust chamber require superalloys for structural integrity, which can add significant weight to the engine.
4. Maintaining Low Temperatures: Balancing system performance with the thermal capabilities of the coolant liners at very low temperatures is a significant challenge.
5. High Development Cost: The development of cryogenic engines is costly, as seen in ISRO’s Cryogenic Upper Stage (CUS) project, which had a budget of Rs 300 crore in 1994.

About CE20 Engine:

1. Developed by: The Liquid Propulsion Systems Centre (LPSC), Valiamala, Kerala.
2. Thrust Output: The CE20 engine has been upgraded to produce a thrust of 20 tonnes, with the capability to generate up to 22 tonnes of thrust for the C32 stage in the future.
3. C32 Stage: A heavier variant of the C20 engine, which will replace the lesser-capacity C25 stage.
4. Successful Missions: The CE20 engine has successfully operated in six successive LVM3 missions, including the Chandrayaan-2 and Chandrayaan-3 missions, along with two commercial OneWeb missions.

• LVM3 (Geosynchronous Satellite Launch Vehicle Mk III): A three-stage vehicle capable of lifting payloads up to 4000 kg.

Cryogenic Engine Comparison with Other Engines:

Characteristic	Cryogenic Engine	Jet Engine	Solid Propellant Engine	Liquid Propellant Engine
Air Intake	No intake required	Air intake required	Air intake required as oxidizer	Air intake required as oxidizer
Fuels	Supercooled Hydrogen and Oxygen	Jet A-1, kerosene, aviation gasoline	Composite propellants with metallic powders	Hydrazine, MMH, UDMH
Fuel Temperature	Very low	No low-temperature requirement	No low-temperature requirement	No low-temperature requirement
Efficient Working	Efficient when low-temperature fuel transforms and mixes correctly	Efficient at supersonic speeds	Efficient with sufficient oxidizer	Efficient with sufficient oxidizer
Purpose	Third/Last stage of rocket	Used in airplanes	Used as boosters in liftoff	Main stage after booster separation

ISRO is exploring the use of start fuel ampules like Tri-ethyl-aluminum (TEA) and Tri-ethyl-boron (TEB) to improve ignition reliability and engine efficiency, taking cryogenic propulsion technology to the next level.

The CE20 cryogenic engine is a vital step forward in ISRO's propulsion capabilities and is crucial for the success of future space missions, including the ambitious Gaganyaan mission.

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