RAS question
A scramjet engine differs from a ramjet in that it:
Correct answer: (B) Compresses air supersonically without slowing it to subsonic speed.
A scramjet differs from a ramjet because the incoming air remains supersonic through the engine instead of being slowed to subsonic speed before combustion.
Explanation
A scramjet is a supersonic-combusting ramjet: the key difference is what happens to the airflow inside the engine. In a scramjet the airflow remains supersonic throughout, while in a ramjet it is slowed to subsonic speed before combustion. The Press Information Bureau, Government of India supports this distinction by stating that both scramjet and ramjet engines use the spacecraft's forward motion to compress incoming air, but the exit flow from the inlet of a ramjet is subsonic, whereas that from a scramjet is supersonic. PIB also notes that both use atmospheric oxygen as the oxidiser, which is why the distinction is not about carrying oxygen or working without air; it is about the speed regime of the compressed airflow.
Why the other options are wrong
- (A) A scramjet is associated with supersonic and hypersonic operation, not low-speed operation; it operates at Mach 5+.
- (C) The issue is not rocket fuel: PIB states that both ramjet and scramjet engines use atmospheric oxygen as the oxidiser, and both use atmospheric air.
- (D) A scramjet cannot be described as air-independent because PIB says both scramjet and ramjet engines use atmospheric oxygen, and they are air-breathing engines.
Concept
This tests propulsion technology under Science and Technology, especially the difference between air-breathing engine types. It recurs in RAS because ISRO demonstrations and basic space-technology concepts are frequent current-science themes.