Scramjet Engine Technology

By Sudheer Kumar K|Updated : November 19th, 2020

India has been working on efficient Rocket Propulsion and Missile Technology for decades. The DRDO started developing a Scramjet engine in the early 2010s. The Indian Space Research Organisation (ISRO) successfully tested a system in 2016. DRDO also conducted a test of this system in June 2019.

 Scramjet Engine Technology

Scramjet stands for Supersonic combustion Ramjet Technology. It is a variant of Air-breathing jet Engines or Air Breathing Propulsion System. The air-breathing propulsion system uses the oxygen present in the atmosphere up to the height of 50 km from earth surface to ignite or burn the fuel stored in the rocket.

A Ramjet uses the engine's forward motion to compress incoming air without a rotating compressor or a centrifugal compressor. But ramjet decelerates the air to subsonic velocities before combustion. However, with an increase in speed, the efficiency of a ramjet starts to drop as the air temperature in the inlet increases due to compression. Hence it is not efficient at supersonic combustion.

A Scramjet is a modified ramjet engine in which combustion takes place in supersonic airflow. This allows the scramjet to operate efficiently at extremely high speeds. Hence the name, Supersonic Combustion Ramjet Engine. Scramjet powered vehicles are expected to operate at speeds up to at least Mach 15.

Significance of Scramjet Engine

  • Earlier, in conventional vehicles, liquefied oxygen was carried by Rockets along with the fuel. But the air-breathing propulsion system need not carry liquid oxygen and hence would enable the launch vehicles to carry heavy satellites.
  • Mastering the air-breathing scramjet technology will lead to the development of hypersonic missiles, faster civilian air transportation and facilities for putting satellites into orbit at a low cost.
  • Scramjet can be used in Reusable Launching Vehicles, which requires efficient combustion

Advantages over the Convention system

  • Reduction in Weight: Since the Scramjet engine uses the oxygen present in the atmosphere to ignite the hydrogen fuel, the amount of oxygen required to be carried onboard is reduced considerably. In a conventional launch vehicle, the propellant accounts for nearly 85% of the weight of a rocket and oxygen accounts for about 60% of the weight of the propellant.
  • Higher Thrust: Rocket powered by scramjet has several times greater trust compared to rockets powered by liquid fuel or cryogenic fuel.
  • Save Costs: Rocket with a scramjet engine would be considerably smaller and thus cheaper.

Technology Demonstration

DRDO successfully tested Hypersonic Technology Demonstrator Vehicle (HRDV), which is a giant leap in indigenous defence technologies and a major breakthrough towards a Sashakt Bharat and Atmanirbhar Bharat. During the demonstration, the hypersonic combustion sustained and the cruise vehicle continued on its intended flight path at a velocity of Mach 6 for a period of 20 seconds.

In 2016, ISRO successfully tested an indigenously developed Scramjet Technology Demonstrator Vehicle. The test flight achieved a speed of Mach 6 and able to maintain ignition for about 6 seconds.

In both cases, the critical events like fuel injection and auto ignition of scramjet demonstrated technological maturity. 


  • Scramjet does not use compressors, instead uses the engine’s forward motion to compress air. Hence it must be boosted to high speed to produce higher thrust. It means the scramjet engine can function only when the rocket goes beyond Mach 5. This is a major challenge in testing the engine at higher Mach speed.
  • Developing technology is very costly.
  • High-Thrust-to-weight.

Way Forward

  • More number of tests are needed to achieve the level of technology with countries like the US, Russia and China.
  • Need to overcome High-thrust-weight ratio to achieve successful flight of a commercial rocket powered by a scramjet engine.

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