Ramjet engine is a very simple air breathing engine (requires atmospheric air to work). It has no moving parts, So less weight easy to built even though it can produce super sonic velocity.Working of the ramjet engine based on Ram Effect.
RAM EFFECT AND RAM PRESSURE
The kinetic energy of air converted into pressure ,this effect is known as ram effect, and the pressure created by this effect is known as ram pressure.
WORKING PRINCIPLE OF RAMJET ENGINE
In a turbo jet engine we need compressor to increase the pressure of the incoming air and the turbine to activate the compressor. But the ramjet engine don’t need compressor to compress the air therefore no need for turbine and any other moving parts.
The ramjet engine compress the air by ram effect. The high speed air enters the diffuser of the ramjet engine, this high speed (supersonic) induces shock waves in the diffuser so the velocity of the incoming air get decreased and the pressure increase.
The diffuser of the ramjet engine can give pressure ratio up to 8 to 10 (pressure after the diffuser/pressure before the diffuser) by using the shock waves. If the incoming velocity increases the effect of diffuser also increases so we can get pressure ratio up to 30.This pressure ratio is more than enough for stable combustion.
So when the air reaches the combustion chamber of the ramjet engine it’s velocity decreased to 0.2 M and have lot of pressure for efficient combustion. The combustion chamber have flame holder and fuel sprayer, The air is mixed with the fuel and combusted. In the ramjet engine have no turbine so we can combust the air upto 1500 to 2000 K (if there is a turbine like turbo jet the high temperature will affect the turbine material so the combustion temperature of the turbojet engine limited to 600 K ).
After the combustion chamber the gas reaches the convergent divergent nozzle section of the ramjet engine, it is the last part of the ramjet engine. Here the gas expanded to reach high jet velocity because of the CD nozzle. The high temperature (1500-2000 K) gives lot of kinetic energy to the gas. This exit velocity is directly proportional to inlet velocity and exit temperature , indirectly proportional to inlet temperature. So the high thrust is scheived at high speed. This is how the ramjet engine produces more thrust and high velocity without any moving parts.
- Easy to built, Maintain
- High combustion efficiency because of high pressure ratio
- Better specific fuel consumption compared to turbo jet engine.
- Zero static thrust
We can not start the ramjet engine in the ground. To start it require high speed inlet velocity to produce shock waves in the diffuser. To achieve that we need a external rocket motor or an aircraft to give initial motion.
- The main part of the Ramjet engine is it’s diffuser so we have to extra careful when design and manufacture the diffuser.
- Due to high airspeed the combustion chamber requires flame holder for continuous combustion.
Mainly used in Super sonic Missiles and fighter aircraft for high speed.
World’s Fastest cruise missile BRAHMOS uses ramjet engine.
SCRAM JET ENGINE – Super sonic Combustion Ramjet
As it’s name in the scramjet engine the combustion takes place at supersonic speed but in the ramjet engine the combustion takes place at subsonic speed.
Scramjet engines are under development and initial testings. They can reach upto Hypersonic Speed.
India uses Scramjet engine in it’s Reusable Launch Vehicle – Technology Demonstrator (RLV-TD)