Why in the News?

The Indian Space Research Organisation's CE20 cryogenic engine passed a critical sea-level test, a breakthrough in its propulsion technology.

More about the news

• The sea-level test implemented a 'Nozzle Protection System' to manage issues like flow separation within the nozzle, which can cause vibrations, thermal problems, and potential damage.
• ISRO has been working on the engine in view of its Gaganyaan mission, India's first manned spaceflight. 
• Test Location: ISRO Propulsion Complex in Mahendragiri, Tamil Nadu.
  • The sea-level test introduced an innovative 'Nozzle Protection System' to address technical challenges in engine restart capability.
• Earlier, HAL had also established the Integrated Cryogenic Engine Manufacturing Facility in Bengaluru, 2023. 

How does a cryogenic engine work?

• The working principle: The thrust is produced by an internal combustion/pressure difference.
  • This follows Newton's Third law of motion- "Every action has an equal and an opposite reaction".
• Uses: Cryogenic engines are used in space launch vehicles, in the last stage (or upper stage) of a rocket. 
  • A Cryogenic engine uses both cryogenic fuel and oxidizer, liquefied at a very low temperature. 
• Fuel: The fuel and oxidizer used in a cryogenic engine are liquefied gases, stored at extremely low temperatures. 
  • Generally liquid hydrogen liquefied at -253° Celsius is used as fuel and liquid oxygen liquefied at -183° Celsius is used as oxidizer.

Note: Semi-cryogenic engine uses refined kerosene instead of liquid hydrogen which offers advantages of lighter weight and storage at normal temperature.

Advantages of cryogenic engine

• Efficiency and Thrust: Compared to solid and earth-storable liquid propellant rocket stages, cryogenic propulsion offers superior thrust, with LOX+LH2 producing maximum energy and lightweight water vapor, resulting in higher performance.
• Fuel Efficiency: Cryogenic engines use less fuel. ISRO's PSLV Vikas engine burns 3.4 kg/sec, while cryogenic engines need only 2 kg/sec for the same thrust. Their specific impulse reaches 450 seconds versus 260 seconds for solid propellants.
• Eco-Friendly Technology: Hydrogen-oxygen combustion emits only steam, making cryogenic propulsion a clean, carbon-free solution.
• Heavy Payloads & Space Missions: High efficiency makes cryogenic fuel ideal for heavy payloads and long missions like Gaganyaan and Chandrayaan.

Some of the challenges in Cryogenic engine technology

• Complex technology: A very complex system compared to solid or liquid propellant stages due to its use of propellants at extremely low temperatures and the associated thermal and structural problems. 
• High thermal gradient and thermal stresses: Problems such as cracks forming on the divergent outer shell, sudden stoppage of rotation, blockages in the channels, distortions in nozzles etc.
• High Operational Pressures: The high operational pressures of thrust chamber coolant circuits and thrust related stresses typically require high strength super alloys for load reaction, ultimately a major engine weight driver.
• Maintaining low temperature: The most significant thrust chamber challenge is balancing system performance with the thermal capability of coolant liners at deep throttle; low coolant flow operation.
• High cost of development: Cryogenic Upper Stage (CUS) project in 1994 had budget of Rs 300 crore.

About CE20

• Developed by: The Liquid Propulsion Systems Centre (LPSC), Valiamala, Kerala.
• Output: It has been upgraded to produce a thrust level of 20 tonnes. Apart from that, it is capable of producing an enhanced thrust of 22 tonnes for the C32 stage in the future.
  • C32 is new and heavier cryogenic upper stage called C32, a variant of the C20 engine that will replace lesser capacity C25 stage.
• Successful Mission: It has demonstrated its capability by successfully operating in six successive LVM3 missions, including the Chandrayaan-2, Chandrayaan-3, and two commercial OneWeb missions.
  • LVM3 (Geosynchronous Satellite Launch Vehicle Mk III) is three-staged vehicle, capable of lifting 4000kg payload.

Cryogenic Engine comparison with other engines

Conclusion

The CE20 Cryogenic engine marks a significant milestone in ISRO's progress with cryogenic technology. Advancing further, ISRO could explore start fuel ampules like Tri-ethyl-aluminum and Tri-ethyl-boron to enhance ignition reliability and efficiency.