Scramjet VS Ramjet

Ramjet engine

A ramjet is a form of air-breathing jet engine that uses the vehicle’s forward motion to compress incoming air for combustion without a rotating compressor. Fuel is injected in the combustion chamber where it mixes with the hot compressed air and ignites.
A ramjet-powered vehicle requires assisted take-off like a rocket assist to accelerate it to a speed where it begins to produce thrust.
Ramjets work most efficiently at supersonic speeds around Mach 3 (three times the speed of sound) and can operate up to speeds of Mach 6.However, the ramjet efficiency starts to drop when the vehicle reaches hypersonic speeds.

Ramjet Is very simple in construction and does not have any moving part such as compressor and turbine.
It is very cheap and requires almost no maintenance.
Greater thrust per unit engine weight than any other propulsion engine at supersonic speed except rocket.
At very high speed and high altitudes the specific fuel consumption is less than turbojet engine
It can be operated with any type of liquid fuels and even with solid nuclear fuels

A scramjet engine is an improvement over the ramjet engine.
Uniqueness about the scramjet technology is that it draws oxygen from the air when the rocket travels through the atmosphere.
Ordinary rockets do the same. They also draw the oxygen from air but they use compressor to draw in air, compress and ignite to burn the fuel. the scramjet’s heating and compression is done by movement of rocket itself as it is moving at supersonic speed. Thus, it is known as Supersonic Combustion Ramjet, or Scramjet.

Does not have to carry oxygen tank.
No rotating parts makes it easier to manufacture.
Less weight and simple design.
As the hydrogen is used as a propellant and combustion is carried out at supersonic velocity with the help of oxygen from the atmosphere.
As a result of that, steam (H2O) is being exhaust gas which is eco-friendly in nature.