ISRO successfully starts testing its semi-cryogenic engine

Context

The Indian Space Research Organisation (ISRO) has successfully begun testing of its semi-cryogenic engine that will power future launch vehicles.

Key-highlights

ISRO has initiated the series of tests required for qualifying and validating its most-powerful liquid-fuelled engine yet, one that is powered by especially refined kerosene (dubbed as 'ISROsene') and super-cooled liquid oxygen.
Once ready, this 2000kN Semicryogenic Engine and its stage (associated components, fuel tanks etc.) will be replacing the current L110 (core stage) of India's largest rocket - Launch Vehicle Mark 3(LVM3).
This is meant to significantly add to the lifting power of the LVM3 rocket.

Why ISRO is focusing on Semi-Cryogenic Engine?

The semi-cryogenic engine is an advancement in rocket technology over the cryogenic engine, which ISRO currently uses for the Geosynchronous Satellite Launch Vehicle (GSLV) which can carry up to 4 tonnes of payload into higher earth orbit.
For increased payload, a cryogenic engine would not be enough and hence the development of semi-cryogenic engines is a key stage in India’s space programme.
Disadvantages posed by cryogenic engines:
- The use of liquid hydrogen at extremely low temperatures is very difficult to store being the smallest gas
- The cost of using liquid hydrogen is a prohibitive
Benefits of Semi-Cryogenic Engine:
- Better fuel: A semi-cryogenic engine uses refined kerosene instead of liquid hydrogen. It uses liquid oxygen as an oxidiser.
  - Kerosene is much lighter than liquid fuel and can be stored at a normal temperature. The Kerosene combined with liquid oxygen provides more thrust to the rocket. Compressed Natural Gas (CNG) can also be used as fuel.
- Less space: It also occupies less space which makes it possible to have more propellant in the fuel compartment or tank.
- It is more environment-friendly, cost-effective and more powerful compared to a cryogenic engine. It can carry a huge weight to a higher altitude. Moreover, the payload can be increased since the weight of the fuel will come down by 500kg.