The Task

Groups working on this task are reminded that they must first offer an abstract or summary to introduce / induct the reader to the event before offering their answers to the questions.


1. What benefits can this discovery bring?

2. What possible negative consequences could arise?

3. How will this discovery change the world?

The scramjet changing the world!?

Since time immemoriable, inventions that are introduced had always brought about changes to the world irregardless of its magnitude of effects. Therefore, the scramjet will definetely change the world.

Yet, how will the world change still needs time for us to find out.......

Short Clip Of The ScramJet

Possible negative consequences

It would be too naive to ignore what negatives effects a scramjet can bring. Personally, I feel that anything will be affected. For example, a country that is not happy with another country will just send a destructive missle flying to the capital of the other country at a very high speed. In a matter of one or two MINUTES, a country may just dissapear like that.....

Scary is not it?

However fret not, this will not be very possible as this just a thought up worst possible scenario by me.

All in all, there are as much as negative effects as positives effects in a scramjet. However, it just depends on its wielder and his purpose. Therefore, the possible negative consequences is subjective to every individual.

Benefits of a scramjet

Owing to its potential, organizations around the world are researching scramjet technology. Scramjets will likely propel missiles first, since that application requires only cruise operation instead of net thrust production. Much of the money for the current research comes from governmental defense research contracts.

One issue is that scramjet engines are predicted to have exceptionally poor thrust to weight ratio- around 2 4. This compares very unfavorably with the 50-100 of a typical rocket engine. This is compensated for in scramjets partly because the weight of the vehicle would be carried by aerodynamic lift rather than pure rocket power (giving reduced 'gravity losses'), but scramjets would take much longer to get to orbit due to lower thrust which significantly offsets the advantage. The takeoff weight of a scramjet vehicle is greatly reduced over that of a rocket, due to the lack of onboard oxidiser, but increased by the structural requirements of the larger and heavier engines.

An aircraft using this type of jet engine could dramatically reduce the time taken to travel from one place to another, thus putting any place on Earth within a 90 minute flight. However, there are controversies about whether such a vehicle could carry enough fuel to make useful long trips.


Theory of a scramjet

All scramjet engines have fuel injectors, a combustion chamber, a thrust nozzle and an inlet, which compresses the incoming air. Sometimes engines also include a region which acts as a flame holder(a component of a jet engine designed to help maintain continual combustion), although the high stagnation temperatures mean that an area of focused waves may be used, rather than a discrete engine part as seen in turbine engines. Other engines use pyrophoric(a substance that ignites spontaneously) fuel additives, such as silane, to avoid such concerns.

An isolator between the inlet and combustion chamber is often included to improve the homogeneity of the flow in the combustor and to extend the operating range of the engine.A scramjet is reminiscent of a ramjet. In a typical ramjet, the supersonic inflow of the engine is decelerated at the inlet to subsonic speeds and then reaccelerated through a nozzle to supersonic speeds to produce thrust. This deceleration, which is produced by a normal shock(a type of propagating disturbance), creates a total pressure loss which limits the upper operating point of a ramjet engine.

For a scramjet, the kinetic energy of the freestream air entering the scramjet engine is large compared to the energy released by the reaction of the oxygen content of the air with a fuel (say hydrogen). Thus the heat released from combustion at Mach 25 is around 10% of the total enthalpy of the working fluid. Depending on the fuel, the kinetic energy of the air and the potential combustion heat release will be equal at around Mach 8. Thus the design of a scramjet engine is as much about minimizing drag as maximizing thrust.The high speed makes the control of the flow within the combustion chamber difficult.

Since the flow is supersonic, no upstream influence propagates within the freestream of the combustion chamber. Therefore, throttling of the entrance to the thrust nozzle is not a usable control technique. In effect, a block of gas entering the combustion chamber must mix with fuel and have sufficient time for initiation and reaction, all the while travelling supersonically through the combustion chamber, before the burned gas is expanded through the thrust nozzle. This places stringent requirements on the pressure and temperature of the flow, and requires that the fuel injection and mixing to be extremely efficient. Usable dynamic pressures lie in the range 20 to 200 kPa (0.2-2 bar),

q=1/2 ρv^2

where q is the dynamic pressure of the gas, ρ (rho) is the density of the gas, v is the velocity of the gas.

Fuel injection and management is also potentially complex. One possibility would be that the fuel is pressurized to 100 bar by a turbo pump, heated by the fuselage, sent through the turbine and accelerated to higher speeds than the air by a nozzle. The air and fuel stream are crossed in a comb like structure, which generates a large interface. Turbulence due to the higher speed of the fuel lead to additional mixing. Complex fuels like kerosene need a long engine to complete combustion.The minimum Mach number at which a scramjet can operate is limited by the fact that the compressed flow must be hot enough to burn the fuel, and of high enough pressure that the reaction is finished before the air moves out the back of the engine. Additionally, in order to be called a scramjet, the compressed flow must still be supersonic after combustion. Here two limits must be observed: Firstly, since when a supersonic flow is compressed it slows down, the level of compression must be low enough (or the initial speed high enough) not to slow down the gas below Mach 1. If the gas within a scramjet goes below Mach 1 the engine will "choke", transitioning to subsonic flow in the combustion chamber. This effect is well known amongst experimenters on scramjets since the waves caused by choking are easily observable.

Additionally, the sudden increase in pressure and temperature in the engine can lead to an acceleration of the combustion, leading to the combustion chamber exploding.Secondly, the heating of the gas by combustion causes the speed of sound in the gas to increase (and the Mach number to decrease) even though the gas is still travelling at the same speed. Forcing the speed of air flow in the combustion chamber under Mach 1 in this way is called "thermal choking". It is clear that a pure scramjet can operate at Mach numbers of 6-8 (e.g 1), but in the lower limit, it depends on the definition of a scramjet. Certainly there are designs where a ramjet transforms into a scramjet over the Mach 3-6 range5 (Dual-mode scramjets). In this range however, the engine is still receiving significant thrust from subsonic combustion of "ramjet" type.

The high cost of flight testing and the unavailability of ground facilities have hindered scramjet development. A large amount of the experimental work on scramjets has been undertaken in cryogenic facilities, direct-connect tests, or burners, each of which simulates one aspect of the engine operation. Further, vitiated facilities, storage heated facilities, arc facilities and the various types of shock tunnels each have limitations which have prevented perfect simulation of scramjet operation. The HyShot flight test showed the relevance of the 1:1 simulation of conditions in the T4 and HEG shock tunnels, despite having cold models and a short test time. The NASA-CIAM tests provided similar verification for CIAM's C-16 V/K facility and the Hyper-X project is expected to provide similar verification for the Langley AHSTF [1], CHSTF [2] and 8 ft HTT.

Computational fluid dynamics has only recently reached a position to make reasonable computations in solving scramjet operation problems. Boundary layer modeling, turbulent mixing, two-phase flow, flow separation, and real-gas aerothermodynamics continue to be problems on the cutting edge of CFD. Additionally, the modeling of kinetic-limited combustion with very fast-reacting species such as hydrogen makes severe demands on computing resources. Reaction schemes are numerically stiff, having typical times as low as 10-19 seconds, requiring reduced reaction schemes.Much of scramjet experimentation remains classified. Several groups including the US Navy with the SCRAM engine between 1968-1974, and the Hyper-X program with the X-43A have claimed successful demonstrations of scramjet technology.

Since these results have not been published openly, they remain unverified and a final design method of scramjet engines still does not exist.The final application of a scramjet engine is likely to be in conjunction with engines which can operate outside the scramjet's operating range. Dual-mode scramjets combine subsonic combustion with supersonic combustion for operation at lower speeds, and rocket-based combined cycle (RBCC) engines supplement a traditional rocket's propulsion with a scramjet, allowing for additional oxidizer to be added to the scramjet flow. RBCCs offer a possibility to extend a scramjet's operating range to higher speeds or lower intake dynamic pressures than would otherwise be possible.


The Scramjet

A scramjet is a type of engine designed to operate at the high speeds usually associated with rocket propulsion. Different from a classic rocket, a scramjet uses air collected from the atmosphere to combust its fuel, as opposed to an oxidizer carried with the vehicle. Normal jet engines and ramjet engines use air collected from the atmosphere in this way. The problem is that collecting air from the atmosphere causes drag, which increases quickly as the speed increases. Also, at high speed, the air collected becomes so hot that the fuel no longer burns efficiently thus producing lesser energy

The scramjet is a proposed solution to both of these problems, by modifying the ramjet design. The main change is that the blockage inside the engine is reduced, so that the air is not slowed down as much. This means that the air is cooler (due to absence of lesser friction), so that the fuel can combust more efficiently. Unfortunately the higher speed of the air means that the fuel has to mix and combust in a very short time, which is difficult to achieve.

To keep up the rate of fuel combustion, the pressure and temperature in the engine need to be kept steady. However, the blockages which were removed were useful to control the air in the engine, and so the scramjet is forced to assume a particular speed for each altitude. This is called a "constant dynamic pressure path" because the wind that the scramjet feels in its face is constant, making the scramjet fly faster at higher altitude and slower at lower altitude.

The inside of a very simple scramjet would look like two kitchen funnels attached by their small ends. The first funnel is the intake, and the air is pushed through, becoming compressed and hot. In the small section, where the two funnels join, fuel is introduced, and the combustion makes the gas become even hotter and more compressed. Finally, the second funnel is a nozzle, like the nozzle of a rocket, and a propulsion is produced.
Note that most artists' impressions of scramjet-powered vehicle designs depict waveriders where the underside of the vehicle forms the intake and nozzle of the engine. This means that the intake and nozzle of the engine are asymmetric and contribute directly to the lift of the aircraft. A waverider is the required form for a hypersonic lifting body.