How does a scramjet work? What led to the development of scramjet? Scramjet was developed because there was no means of providing hypersonic speed within the atmosphere, other than the rocket engine. The problem with rocket engine is, although it can range in speed from subsonic speed to hypersonic speed, its use within the atmosphere is not economical and viable. Rocket engine carries it's own oxidizer along with fuel. This not only make it heavy but also limit it's payload carrying capability. Besides, the longer distance the rocket has to travel, the heavier and larger it has to become to carry additional fuel and oxidiser. Although reuseable rocket engine is under development but largely rockets are for one time use only. To fill this gap of hypersonic speed within the atmosphere that too with fuel efficiency, gave birth to scramjet.
Scramjet stands for supersonic combustion ramjet and is the engine where combustion take place in hypersonic speed. Scramjet consists of converging inlet, combustion chamber, fuel injectors and diverging exhaust duct. The scramjet cannot work at low speed, so it require the assistance of rocket, turbojet and similar engines, to take it to the speed from where it can operate on its own. Usually to the speed of Mach 6 to 8 (but there are also scramjet which can operate from speed of Mach 3 to 6). So how does a scramjet work? The air flowing to the inlet of scramjet is slowed down but the airflow still remains supersonic. After combustion the exhaust is released at even greater speed.
So the question arises how the combustion is possible at supersonic speed? Firstly, some engines have a region which behave like a flame holder. Secondly, some other engines use pyrophoric fuel additives like silane to avoid flame out. Thirdly, yet some engines have an isolator between the inlet and compressor for better homogeneous mixing as well as maintaining the supersonic speed at combustion. So how the heat is provided for combustion. The heat is provided by compression of the air. And when the fuel is injected to this compressed air, combustion take place. The exhaust gas is accelerated to a greater speed than the incoming air.
WATCH THE FOLLOWING VIDEO TO KNOW ABOUT HOW DOES A SCRAMJET WORK:
Advantages of scramjet are as follows. Firstly, no need to carry separate oxidising agent. Secondly, no moving parts like compressor, turbine etc. is required. Thirdly, a possible hypersonic speed which will reduce the travel time in the world significantly. Fourthly, a possible cheaper outer space travel. Fifthly, fuel savings when compared to rocket engine. Sixthly, greater payload carrying capability when compared to rocket engine. Seventhly, scramjet is reuseable.
Disadvantages of scramjet are as follows. Firstly, the scramjet require an initial help from another engine to help it reach the speed from which it is operable. Secondly, research, testing and development activities of scramjet is costly. Thirdly, scramjet engine will experience aerodynamic heating. Fourthly, scramjet will cause sonic boom problems as well.
Scramjet engine will change our travel experience in a way that was never seen before. But scramjet has a long way to go before being commercially viable.
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