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Scramjet EnginesByIshan K PatelBTech-Aerospace Eng.(Vth Sem)A50105513008

What is A Scramjet Engine?

• A scramjet (supersonic combustion ramjet) engine is variant of a ramjet air

breathing combustion jet engine in which the combustion process takes place in

supersonic airflow.

• As in ramjet, a scramjet relies on high vehicle speed to forcefully compress and

decelerate the incoming air before combustion (hence called ramjet), but

whereas a ramjet decelerates the air to subsonic velocities before combustion,

airflow in a scramjet is supersonic throughout the entire engine.

• The fastest air-breathing plane is a SCRAM jet design, the NASA X-43A which reach Mach 9.8.

COMPONENTS OF SCRAMJET ENGINE

The scramjet is composed of three basic components :

1) A Converging Inlet, where incoming air is compressed and decelerated.

2) A Combustor, where gaseous fuel is burned with atmospheric oxygen to produce heat.

3) A Diverging Nozzle, where the heated air is accelerated to produce thrust.

• In scramjets, the engine inlet is designed so it doesn’t create as much compression as in ramjet, allowing the air to zip through the engine at supersonic speeds.

• The simplest type of air breathing engine is the scramjet engine and simplified sketch of engine is given in figure.

PRINCIPLE OF WORKING

• Scramjets works on the same principle of ramjet.

• All the operations done by the varying cross section of passages.

• There are inlet passage, diffuser passage, combustion passage and exhaust passage.

• Basically in order to achieve the initial speed, a second engine is integrated in the Scramjet model, it may be rocket or turbojet engine.

PRINCIPLE OF WORKING (Cont.)

• As these are air breathing engines, air from the atmosphere enters at very high speed in the inlet passage.

• In case of a scramjet the diffuser is merged with inlet.

• Hence the air from the atmosphere enters in the inlet section having very high velocity reduced in diffuser section; thereby its static pressure increases.

• Temperature of air also increases when passing through the narrow cross section towards the combustion chamber.

PRINCIPLE OF WORKING

• Hot air flows in the combustion chamber and at this moment the propellant i.e. hydrogen (having a very low ignition temperature) are injected by the injector in the combustor, where it gets self ignited within a millisecond and the combustion process is carried out at supersonic speed.• The fresh air supply to the diffuser builds up a pressure at the diffuser

so that these burned gases cannot expand towards the diffuser. Instead the gases are made expand in combustor towards tail engine hence providing the required thrust.

ADVANTAGES

• Does not have to carry oxygen.• No rotating parts, makes it easier to manufacture.• Less weight and simple design.• As the hydrogen is used as a propellant combustion is carried out at

supersonic velocity with the help of oxygen from the atmosphere. As a result of that, steam is being exhaust gas which is eco-friendly in nature.

DISADVANTAGES

• A scramjet cannot produce efficient thrust unless boosted to high speed, around Mach 5.

• As a result an additional propulsion systems are required.

• Lack of stealth.

• Testing difficulties.

RECENT DEVELOPMENTS

• Hyper-X “Scramjet” A new program, called Hyper-X, was launched by NASA in 1997. The goal is to build working jet airplanes that use a clever combination of ramjet, scramjet, and rocket engines to reach sufficient speeds to achieve orbit around the earth. These planes would be conventional rocket engines to get started and then switch over to ramjet power at Mach 2 or 3, and then scramjet power at about Mach 5.

Hyshot “Scramjet”

The university of Queensland in Australia launched a hypersonic “scramjet” on 30th July 2002, claiming a world’s first revolutionary engine that could bone day propel airliner at 8000 km/hr or more.

Avatar “Scramjet”

AVTAR stands for “Aerobic Vehicle for Advanced Trans Atmospheric Research”. In July 2002, it had been announced that AVTAR is the hyperplane concept that had been developed by India, through support from the DRDO .