Cryogenic engines find applications in

Cryogenic engines are specifically rocket propulsion systems that use liquefied gases (cryogenic propellants such as liquid hydrogen and liquid oxygen) stored at very low temperatures to achieve high specific impulse and efficiency. Textbook material on space programmes lists production of cryogenic propellants as a core element of launch vehicle capabilities [1]. Technical reviews and papers explicitly describe cryogenic technology as pivotal for rocket propulsion, noting LOX/LH2 engines and their performance advantages in launch vehicles and deep-space missions. Independent educational summaries likewise state that cryogenic engines are a type of rocket engine; submarine propulsion and frost-free refrigerators do not employ cryogenic engines, while superconductivity research uses cryogenic cooling systems but not “engines” in the propulsion sense.

Sources

1. [1] Indian Economy, Nitin Singhania .(ed 2nd 2021-22) > Chapter 14: Service Sector > 14.12 Indian Economy > p. 434