Ramjet vs Scramjet


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1 min read

Prelims: General Science

Mains: Achievements of Indians in science & technology; indigenization of technology and developing new technology. 

Ramjet and Scramjet are types of experimental engines designed for speeds greater than those of sound, i.e., for the supersonic and hypersonic realms, respectively. They are jet engines with no moving parts, relying on the enormous pressures created by supersonic airflow into the engine to ignite fuel without needing the compressors and turbines used in the turbofan engines found on conventional jet planes.

Jet engines are a class of internal-combustion engines that propel aircraft by utilising the rear-ward discharge of a jet of fluid, usually hot exhaust gases generated by burning fuel with air drawn in from the atmosphere.

What are Jet Engines?

A jet engine is an internal combustion engine that propels aircraft using the rearward discharge of a jet of fluid, usually hot exhaust gases generated by burning fuel with air drawn in from the atmosphere.

Types of Jet Engines


- Oldest and basic types of jet engines

- It compresses air through a turbine and then burns fuel in the combustion chamber. 

- The thrust generated by this process propels the aircraft forward.


- Uses a gas turbine to power the propeller. 

- Used in smaller aircraft which require low speeds and low altitudes

- Unlike turbojets, it generates thrusts via their propeller.


- Commonly found in commercial aircrafts

- It is a fusion of turbojet and turboprop engines. 

- A portion of the air in this engine bypasses the combustion chamber and is directed towards the engine core, producing additional thrust.


- It is an air breathing propulsion engine operating on the principle of supersonic combustion.

- It has the absence of any rotator and relies solely on the forward motion of the engine to compress incoming air.


- It is an upgraded version of the Ramjet and generates thrust through supersonic air flow and combustion.

- It moves at hypersonic speed and performs best at high speeds, greater than Mach 5.


- This basic jet engine is the most inefficient of all. 

- It has no moving parts.

- It generates a pulsating thrust through the combustion bursts. 

- It is frequently used in rockets and model aircrafts.

  • Processes involved in Jet Engines: The following are the three processes involved in Jet Engines:
    • Combustion: This is the process in which fuel is mixed with compressed air and gets ignited which then produces a high-velocity exhaust.
    • Compression: In this process, the incoming air is compressed to increase its pressure before entering the combustion chamber.
    • Exhaust: In this process, the high-velocity exhaust gases exit the engine, creating the thrust required to propel the engine.

turbojet, ramjet and scramjet engines

Ramjet Engine

A ramjet engine is a jet propulsion system that utilises the exhaust velocity of a combustion process to achieve thrust.

  • Unlike turbojets, ramjet engines do not require an external compressor and turbine, instead relying solely on the speed of incoming air to ignite fuel in the combustion chamber and create thrust.
    • This makes them an efficient option for high-speed applications, as they can be smaller and lighter than traditional turbojets while delivering comparable performance.
  • The Ramjet engine has no moving parts and relies on high-speed motion for operation.
  • It operates efficiently at supersonic speeds (around Mach 3 to 6).

ramjet engine

Advantages of Ramjet

The Ramjet engines offer several advantages over traditional turbojets, such as,

  • They have a compact size and lightweight construction.
  • They do not require external compressors or turbines, as ramjets use the speed of incoming air to ignite fuel.
  • They are more efficient for high-speed applications than turbojets.

Disadvantages of Ramjet

The Ramjet engines have some drawbacks, such as,

  • They are likely to be inefficient at low airspeeds and may require large intakes to ensure efficient operation.
  • They require a considerable amount of fuel compared to traditional turbojets, which are often more expensive to operate and maintain.

Scramjet Engine

A scramjet engine is an upgraded variant of a ramjet where combustion occurs due to supersonic airflow.

  • This supersonic flow allows the jets to achieve even faster speeds than the standard ramjets.
    • This engine does not need to slow the incoming air for combustion like a typical turbojet or even ramjet.
  • It carries liquid Hydrogen as fuel and liquid Oxygen for combustion (oxidiser) to generate thrust.
  • The fuel efficiency of the scramjets tends to be significantly better than that of traditional turbojets and ramjets.
    • It makes them ideal for various high-speed applications.
  • Due to the complexities of maintaining the supersonic airflow, scramjets are often more expensive and difficult to manage than other engines.
  • They operate more efficiently at very high speeds (Mach 12 to 24).
  • Just like the Ramjet engines, they also have no moving parts.

scramjet engine

Advantages of Scramjet

The Scramjet engines offer some distinct advantages over other types of jet engines, such as,

  • The primary benefit is the potential for increased speed, as combustion takes place in supersonic airflow and does not need to be slowed down for combustion.
  • They are also more fuel-efficient.
  • They could potentially improve the performance during acceleration.

Disadvantages of Scramjet

The scramjets come with their drawbacks, such as,

  • It does not have a compressor to compress the air; hence, it uses its high-speed forward motion to compress the air. Therefore, efficient thrust is difficult to produce unless boosted to high speed.
  • The tolerances required to maintain supersonic airflow often make them harder to manage.
  • They are more expensive than other types of jet engines.
  • These engines can also sacrifice some thrust compared to traditional turbojet and ramjet designs.

Application of Scramjet in Defence

  • The Scramjet engine is the central piece of many high-end applications in Defence such as Hypersonic Cruise Missiles and Hypersonic Glide Vehicles (a warhead for Ballistic Missiles).
  • Many countries have successfully developed hypersonic cruise missiles. 
    • For example, Russia’s Zircon missile and China’s DF-27.
  • HGVs use scramjet engines after achieving supersonic speed to attain the hypersonic speed of the missile. For example, China’s HGV DF-ZF.
  • Russia’s Hypersonic Glide Vehicle (HGV) Avangard has a speed of up to 20 Mach.

Ramjet vs Scramjet

The Ramjet and Scramjet engines have the following differences:

Airflow/ CombustionUses subsonic combustionUses supersonic combustion.
Speed Range1 to 6 Mach (in theory)12 to 24 Mach (in theory), due to a higher specific impulse than a ramjet engine.
EfficiencyIt works best at Supersonic SpeedsIt works best at Hypersonic Speeds

The Ramjet and Scramjet engines both have their unique advantages and disadvantages, as Ramjets excel in applications where efficiency and simplicity are crucial, while Scramjets offer unmatched speed and fuel efficiency but come with increased complexity and cost. The choice between these two technologies depends on the specific requirements of the project and the trade-offs a designer is willing to make.

Ramjet and Scramjet Engines in India

Due to several advantages of the Air Breathing Propulsion System (Ramjet and Scramjet), India has been working on such technologies to be used in the Space as well as Defence sectors.

  • Air Breathing Propulsion Project (ABPP) for Space:
  • In 2016, ISRO successfully tested two indigenously developed scramjet engines through the Scramjet Propulsion Experiment (SPEX).
  • ISRO wants to use rockets fitted with scramjets because their launching cost will be much less than that of conventional rockets.
    • It will be able to carry heavier satellites.
  • In 2023, India became the fourth country to successfully demonstrate the flight testing of a Scramjet Engine.
    • This engine was carried by an Advanced Technology Vehicle (ATV) and demonstrated hypersonicflight at Mach 6.
  • ISRO would likely use this in its future projects for Reusable Launch Vehicles.
  • ISRO is working on the three concepts of ABBP, i.e., Ramjet, Scramjet and Dual Mode Ramjet (DMRJ).
    • A dual-mode ramjet (DMRJ) is a jet engine where a ramjet transforms into a scramjet over Mach 4-8 range and it can efficiently operate both in subsonic and supersonic combustor modes.
  • In Defence Sector:
    • In 2020, DRDO achieved the hypersonic speed of Mach 6 (for 20 sec) through its cruise vehicle, the Hypersonic Technology Demonstrated Vehicle (HSTDV), propelled by an air-breathing scramjet engine.
    • India’s progress in ramjet engine development is impressive. In 2021, India successfully tested a solid fuel ducted ramjet (SFDR) engine at a defence facility located near the Odisha coast.
      • It is designed to be used in missiles and can reach speeds of up to Mach 3.5, demonstrating India’s commitment to developing cutting-edge aerospace technology.

The development of the engines is still in its early stages but has the potential to revolutionise the aerospace industry. India will need to continue investing in research and development to make this technology a reality.

FAQs on Ramjet vs Scramjet

What is the difference between Scramjet and Ramjet?

A scramjet is a ramjet with supersonic combustion. In ordinary ramjets, the air is decelerated to subsonic velocities before combustion, but this is not the case in a scramjet.

What is the speed of Ramjets and Scramjet engines?

Ramjets have a velocity range of 1 to 6 Mach in theory, but Scramjets have a range of 12 to 24 Mach in theory.

What is the difference between a Jet engine and a Ramjet engine?

Jet engines operate by compressing incoming air using a turbine and then combining it with fuel for ignition. But a ramjet engine doesn't have mechanical compressors; it relies on the forward motion of the vehicle itself to compress incoming air.

Is Scramjet faster than Ramjet?

Scramjet is distinguished from the ramjet by the fact that combustion occurs at supersonic air velocity inside the engine. This enables the scramjet to attain higher speeds than a traditional ramjet.

Does India have a Scramjet?

India is the fourth country to demonstrate the flight testing of a Scramjet Engine.

What speed is hypersonic?

The term 'hypersonic speed' is widely defined as any speed beyond Mach 5, meaning five times faster than the speed of sound.