14012013121404-scramjet-engine

Seminar Report SCRAMJET

CONTENTS:1. INTRODUCTION

2. HISTORY OF THE SCRAMJET

3. THEORY

4. ABOUT THE ENGINE

5. OPERATIONS

6. ABOUT THE FUEL USED

7. APPLICATIONS

8. HYPERSONIC SCRAMJET VEHICLES

9. RECENT PROGRESS 10. CONCLUSION

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Seminar Report SCRAMJET

THE SCRAMJET ENGINEINTRODUCTION

One thing has always been true about rockets: The farther and

faster you want to go, the bigger you rocket needs to be.

Why? Rockets combine a liquid fuel with liquid oxygen to create

thrust. Take away the need for liquid oxygen and your spacecraft

can be smaller or carry more pay load.

That's the idea behind a different propulsion system called

"scramjet," or Supersonic Combustion Ramjet

The oxygen needed by the engine to combust is taken from the

atmospheric air passing through the vehicle, instead of from a

tank onboard

Its mechanically simple as it has no moving parts.

All this makes the craft smaller, lighter, faster and have more room

to carry payload.


Seminar Report SCRAMJETHISTORY OF SCRAMJET

During and after World War II, tremendous amounts of time and effort

were put into researching high-speed jet- and rocket-powered aircraft.

The Bell X-l attained supersonic flight in 1947, and by the early

1960s, rapid progress towards faster aircraft suggested that

operational aircraft would be flying at "hypersonic" speeds within a

few years. Except for specialized rocket research vehicles like the

American X-15 and other rocket-powered spacecraft, aircraft top

speeds have remained level, generally in the range of Mach 1 to Mach

2.

In the realm of civilian air transport, the primary goal has been

reducing operating cost, rather than increasing flight speeds. Because

supersonic flight requires significant amounts of fuel, airlines have

favored subsonic jumbo jets rather than supersonic transports. The

production supersonic airliners, the Concorde and Tupolev Tu-144

operated at a financial loss (with the possible exception of British

Airways that never opened the accounts). Military aircraft design

focused on maneuverability and stealth, features thought to be

incompatible with hypersonic aerodynamics.

Hypersonic flight concepts haven't gone away, however, and low-level

investigations have continued over the past few decades. Presently,

the US military and NASA have formulated a "National Hypersonics

Strategy" to investigate a range of options for hypersonic flight. Other

nations such as Australia, France, and Russia have also progressed in

hypersonic propulsion research.


Seminar Report SCRAMJETDifferent U.S. organizations have accepted hypersonic flight as a

common goal. The U.S. Army desires hypersonic missiles that can

attack mobile missile launchers quickly. NASA believes hypersonics

could help develop economical, reusable launch vehicles.


Seminar Report SCRAMJETThe Air Force is interested in a wide range of hypersonic systems,

from air-launched cruise missiles to orbital spaceplanes, that the

service believes could bring about a true "aerospace force."

The University of Queensland, Australia reported in 1995 the first

development of a scramjet that achieved more thrust than drag[l] and

in 2002 successfully tested the HyShot Scramjet system.

And the most recent successful tests were achieved by NASA's

Hyper-X project in 2004 (around Mach 10). Currently research and

development is going on for a craft that can break the Mach 10 barrier.

THEORY

What is a scramjet?

In a conventional ramjet, the incoming supersonic airflow is slowed to

subsonic speeds by multiple shock waves, created by back-pressuring

the engine. Fuel is added to the subsonic airflow, the mixture

combusts, and exhaust gases accelerate through a narrow throat, or

mechanical choke, to supersonic speeds. By contrast, the airflow in a

pure scramjet remains supersonic throughout the combustion process

and does not require a choking mechanism, which provides optimal

performance over a wider operating range of Mach numbers. Modern

scramjet engines can function as both a ramjet and scramjet and

seamlessly make the transition between the two.


Seminar Report SCRAMJETAbout MACH Number and Speed of Sound

As an aircraft moves through the air, the air molecules near the

aircraft are disturbed and move around the aircraft. Exactly how the

air re-acts to the aircraft depends upon the ratio of the speed of the

aircraft to the speed of sound through the air. Because of the

importance of this speed ratio, aerodynamicists have designated it

with a special parameter called the Mach number in honor of Ernst

Mach, a late 19th century physicist who studied gas dynamics.

Basic Definitions:

speed of sound: The speed of sound is a basic property of the

atmosphere that changes with temperature. For a given set of

conditions, the speed of sound defines the velocity

t which sound waves travel through a substance, such as air.

Scientists have devised a standard atmosphere model that

defines typical values for the speed of sound that change with

altitude.

Mach number: Mach number is a quantity that defines how

quickly a vehicle travels with respect to the speed of sound. The

Mach number (M) is simply the ratio of the vehicle's velocity

(V) divided by the speed of sound at that altitude (a).

For example, an aircraft flying at Mach 0.8 is traveling at 80%

of the speed of sound while a missile cruising at Mach 3 is

traveling at three times the speed of sound.

Different speed regions:

subsonic: A vehicle that is traveling slower than the speed

of sound (M

Seminar Report SCRAMJETand the flow is said to be transonic.

supersonic: A vehicle that is traveling faster than the

speed of sound (M>1) is said to be flying at supersonic

speeds.

sound barrier: The term sound barrier is often associated

with supersonic flight. In particular, "breaking the sound

barrier" is the process of accelerating through Mach 1 and

going from subsonic to supersonic speeds.

hypersonic: For speeds greater than five times the speed

of sound, M > 5, the flow is said to be hypersonic.


About the Engine

The scramjet provides the most integrated engine-vehicle design for aircraft

and missiles. The engine occupies the entire lower surface of the vehicle

body. The propulsion system consists of five major engine and two vehicle

components: the internal inlet, isolator, combustor, internal nozzle, and fuel

supply subsystem, and the craft's forebody, essential for air induction, and

aftbody, which is a critical part of the nozzle component.

The high-speed air-induction system consists of the vehicle forebody and

internal inlet, which capture and compress air for processing by the engine's

other components. Unlike jet engines, vehicles flying at high supersonic or

hypersonic speeds can achieve adequate compression without a mechanical

compressor. The forebody provides the initial compression, and the internal

inlet provides the final compression. The air undergoes a reduction in Mach

number and an increase in pressure and temperature as it passes through

shock waves at the forebody and internal inlet.

The isolator in a scramjet is a critical component. It allows a supersonic flow

to adjust to a static back-pressure higher than the inlet static pressure. When

the combustion process begins to separate the boundary layer, a

precombustion shock forms in the isolator. The isolator also enables the

combustor to achieve the required heat release and handle the induced rise in

combustor pressure without creating a condition called inlet unstart, in which

shock waves prevent airflow from entering the isolator.

The combustor accepts the airflow and provides efficient fuel-air mixing

at several points along its length, which optimizes engine thrust.

The expansion system, consisting of the internal nozzle and vehicle aftbody,

controls the expansion of the highpressure, high-temperature gas mixture to

produce net thrust. The expansion process converts the potential energy

generated by the combustor to kinetic energy.

The important physical phenomena in the scramjet nozzle include flow

chemistry, boundarylayer effects, nonuniform flow conditions, shear-layer

interaction, and three-dimensional effects. The design of the nozzle has a

major effect on the efficiency of the engine and the vehicle, because it

influences the craft's pitch and lift.

Changing from subsonic to supersonic combustion, 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 minimising drag as maximising thrust.

Operations

An air-breathing hypersonic vehicle requires several types of engine

operations to reach scramjet speeds. The vehicle may utilize one of several

propulsion systems to accelerate from takeoff to Mach 3. Two examples are a

bank of gas-turbine engines in the vehicle, or the use of rockets, either

internal or external to the engine. At Mach 3-4, a scramjet transitions from

low-speed propulsion to a situation in which the shock system has sufficient

strength to create a region(s) of subsonic flow at the entrance to the

combustor. In a conventional ramjet, the inlet and diffuser decelerate the air to

low subsonic speeds by increasing the diffuser area, which ensures complete

combustion at subsonic speeds. A converging- diverging nozzle behind the

combustor creates a physical throat and generates the desired engine thrust.

The required choking in a scramjet, however, is provided within the

combustor by means of a thermal throat, which needs no physical narrowing

of the nozzle. This choke is created by the right combination of area

distribution, fuel-air mixing, and heat release.

During the time a scramjet-powered vehicle accelerates from Mach 3 to 8, the

airbreathing propulsion system undergoes a transition between Mach 5 and 7.

Here, a mixture of ramjet and scramjet combustion occurs. The total rise in

temperature and pressure across the combustor begins to decrease.

Consequently, a weaker precombustion system is required, and the

precombustion shock is pulled back from the inlet throat toward the entrance

to the combustor. As speeds increase beyond Mach 5, the use of supersonic

combustion can provide higher performance .

Engine efficiency dictates using the ramjet until Mach 5-6. At arou

nd Mach 6, decelerating airflow to subsonic speeds for combustion

results in parts of the airflow almost halting, which creates high

pressures and heat-transfer rates. Somewhere between Mach 5 and

6, the combination of these factors indicates a switch to scramjet

operation. When the vehicle accelerates beyond Mach 7, the

combustion process can no longer separate the airflow, and the

engine operates in scramjet mode without a precombustion shock.

The inlet shocks propagate through the entire engine. Beyond Mach

8, physics dictates supersonic combustion because the engine cannot

survive the pressure and heat buildup caused by slowing the airflow

to subsonic speeds.

Scramjet operation at Mach 5-15 presents several technical

problems to achieving efficiency. These challenges include fuel-air

mixing, management of engine heat loads, increased heating on

leading edges, and developing structures and materials that can

withstand hypersonic flight. When the velocity of the injected fuel

equals that of the airstream entering the scramjet combustor, which

occurs at about Mach 12, mixing the air and fuel becomes difficult.

And at higher Mach numbers, the high temperatures in the

combustor cause dissociation and ionization. These factors

coupled with already-complex flow phenomena such as supersonic

mixing, isolator- combustor interactions, and flame propagation

pose obstacles to flow-path design, fuel injection, and thermal

management of the combustor.

Several sources contribute to engine heating during hypersonic

flight, including heating of the vehicle skin from subsystems such as

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the engine in hypersonic vehicles because of its potential for

extremely high heat loads.

The engine represents a particularly challenging problem because the flow

path is characterized by very high thermal, mechanical, and acoustic loading,

as well as a corrosive mix of hot oxygen and combustion products. If the

engine is left uncooled, temperatures in the combustor would exceed 5,000 F,

which is higher than the melting point of most metals. Fortunately, a

combination of structural design, material selection, and active cooling can

manage the high temperatures.

Hypersonic vehicles also pose an extraordinary challenge for structures and

materials. The airframe and engine require lightweight, high-temperature

materials and structural configurations that can withstand the extreme

environment of hypersonic flight.

The challenges include:

Very high temperatures

Heating of the whole vehicle

Steady-state and transient localized heating from shock waves

High aerodynamic loads

High fluctuating pressure loads

The potential for severe flutter, vibration, fluctuating and thermally-induced

pressures

Erosion from airflow over the vehicle and through the engine

About the Fuel used

The scramjet is an airbreather, meaning that it gets its oxygen from the

surrounding air. However, the scramjet is significantly different from other

kinds of jet engines, like turbojets and ramjets, in one key way. In most jets,

the air pulled into the engines is slowed below Mach 1 and is combusted at

subsonic speeds. The air within the scramjet combustion chamber, however,

remains supersonic. The challenge of making a scramjet work is properly

mixing the high-speed air with fuel while combusting and expanding that

mixture before it exits the tail of the vehicle. This process typically occurs in

less than 1 millisecond (0.001 seconds). Furthermore, the scramjet must burn

enough fuel to generate an enormous amount of energy needed to overcome

the tremendous drag forces experienced when flying at hypersonic speeds.

In order to make a scramjet work, researchers must choose a fuel that can burn

rapidly and generate a large amount of thrust. Hydrogen meets these criteria.

One way to illustrate the differences between various fuels and their energy

content is a measurement called the Lower Heating Value (LHV). The LHV

describes the amount of energy released when a fuel is combusted and all of

the remaining combustion products remain in gaseous form. The LHV for

hydrogen is 119,600 kJ/kg. JP-8, another fuel commonly used in military

aircraft, has a LHV of only 43,190 kJ/kg, less than half that of hydrogen.

Simply put, hydrogen provides more "bang" per kilogram than JP-8, or any

other hydrocarbon fuel for that matter.

There are also other advantages to using hydrogen as a fuel. First of all,

hydrogen is extremely flammable; it only takes a small amount of energy to

ignite it and make it burn. Hydrogen also has a wide flammability range,

meaning that it can burn when it occupies anywhere from 4% to 74% of the

air by volume. Since hydrogen is a gas, it mixes very easily with air allowing

for very efficient combustion. Another advantage over hydrocarbon-based

fuels like JP-8 or gasoline is that hydrogen does not produce any harmful

pollutants like carbon monoxide (CO), carbon dioxide (C02), or particulate

matter during the combustion process. It is for this reason alone that many

researchers have promoted hydrogen as a fuel in the public transportation

industry.

Nevertheless, there are some disadvantages to using hydrogen as a fuel in

aerospace vehicles. Hydrogen is not a dense fuel. At standard pressure and

temperature, it has a density of only 0.09 kg/m3. Compare that to the density

of gasoline at 750 kg/m3 or JP-8 at 800 kg/m3. While this low density is an

advantage in terms of saving weight, hydrogen requires a large volume in

order to store an adequate amount of chemical energy for practical use.

Hydrogen gas is typically stored under pressure to increase its density, but

even at 10,000 psi (68,950 kPa) it will contain only a quarter of the chemical

energy stored in an equivalent volume of JP-8.

The density of hydrogen can be further increased by cooling and pressurizing

the substance to the point that it becomes a liquid, but even in this form it will

need a tank approximately twice the size of that required by JP-8. In addition,

the cost and safety issues involved in manufacturing and storing

cryogenically-cooled fuel is another major drawback. Despite the clear

advantages of hydrogen described earlier, more energy can often be stored in

smaller volumes using denser fuels. As a result, vehicles burning denser

hydrocarbon fuels can usually fly longer distances than those using hydrogen.

APPLICATIONS

Seeing its clear 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

defence research contracts.

Space launch vehicles may benefit from having a scramjet stage. A scramjet

stage of a launch vehicle theoretically provides a specific impulse with 1000 to

4000 s whereas a rocket provides less than 600 s whilst in the atmosphere [1],

potentially permitting much cheaper access to space.

One issue is that scramjets are predicted to have exceptionally poor thrust to

weight ratio- around 2 . This compares unfavourably with a typical rocket

engine that is usually 50-100. 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 which offsets the advantage.

Whether this vehicle would be reusable or not is still a subject of debate and

research.

An aircraft using this type of jet engine could dramatically reduce the time it

takes to travel from one place to another, potentially putting any place on

Earth within a 90 minute flight. However, there are questions about whether

such a vehicle could carry enough fuel to make useful length trips, and there

are obvious issues with sonic booms and acceptable g-loads on passengers.

Hypersonic SCRAMJET vehicle applications

National Aerospace Plane (NASP) and X-30: During the 1980s, NASA began

considering a hypersonic single-stage-to-orbit (SSTO) vehicle to replace the

Space Shuttle. The proposed National Aerospace Plane (NASP) would take

off from a standard runway using some kind of low speed jet engine. Once the

aircraft had reached sufficient speed, air-breathing ramjet or scramjet engines

would power the aircraft to hypersonic velocities (Mach 20 or more) and to

the edge of the atmosphere. A small rocket system would provide the final

push into orbit, but the attractiveness of the concept was using the atmosphere

to provide most of the fuel needed to get into space. NASP eventually

matured into the X-30 research vehicle, which used an integrated scramjet

propulsion system.

The X-30 was intended to replace the Space Shuttle but was cancelled in

the early 1990s due to escalating costs and lack of military support.

X-43 Hyper-X: NASA's Hyper-X project, now known as the X-43 will be

the first vehicle using an air-breathing engine ever flight tested at hypersonic

speeds.Looking much like a scaled-down X-30, the Hyper-X is a small,

unpiloted vehicle intended to test an integrated scramjet engine from Mach 7

to 10. To become airborne, the X-43 will be mounted on the nose of a

Pegasus rocket carried aloft and released by a B-52. The Pegasus will power

the test craft to about 100,000 ft and the desired test speed before the X-43

separates and its scramjet engine engages. The Hyper-X will only fly for a

few seconds before falling into the ocean, but data collected from these test

flights will be used to develop practical hypersonic scramjet engines for

future vehicles.

The first X-43 test flight, conducted in June 2001, ended in failure after the

Pegasus booster rocket became unstable and went out of control. In addition,

three follow-on models are also being considered. First of these is the X-43C

which will test a hydrocarbon-fueled dual mode scramjet being developed by

Pratt & Whitney under the Air Force's HyTech program. The HyTech engine is

expected to accelerate the enlarged X-43C from Mach 5 to Mach 7.

Two propulsion concepts are currently being considered for an X-43B model.

First of these is a rocket-based combined cycle (RBCC) engine under

development by Aerojet, Boeing, Pratt & Whitney, and Rocketdyne. The

RBCC engine is a new technology using a rocket engine fed by oxygen from

the atmosphere rather than carried aboard the vehicle. The effort is being

funded by NASA Marshall under the Integrated Systems Test of an

Airbreathing Rocket (ISTAR) program. Meanwhile, an alternative propulsion

arrangement is being developed at NASA Glenn as part of the Revolutionary

Turbine Accelerator (RTA) program. The RTA engine uses a turbine-based

combined cycle (TBCC) to push turbojet technology to much higher speeds

than is possible with current jet engines. Regardless of the engine eventually

selected, plans call for the vehicle to be air-launched at Mach 0.8 and

accelerate to Mach 7 or 8 over 10 minutes. The RTA engine would accerate to

about Mach 5 where a HyTech engine like that used on the X-43C would take

over. Both the RBCC and TBCC vehicles would be able to glide down for

landing and reuse permitting up to 25 flights.

A final proposal is for an X-43D, an evolved version of the original X-43 A.

While the X-43 A is powered by an uncooled hydrogen-fueled scramjet

engine, the X-43D would use a cooled, liquid-hydrogen-fueled scramjet. The

upgraded engine would provide 10 seconds of power and be capable of

accelerating to Mach 15.

Commercial Transports: Hypersonic vehicles in general and waveriders in

particular have long been touted as potential high-speed commercial

transports to replace the Concorde. Some aerospace companies, airlines, and

government officials have proposed vehicles cruising at Mach 7 to 12 capable

of carrying passengers from New York to Tokyo in under two hours.

Military Applications: Probably the greatest proponent of hypersonic travel

over the years has been the United States military. Trends of the 1950s and

1960s indicated that military aircraft had to fly faster and higher to survive, so

concepts for high-altitude fighters and bombers cruising at Mach 4 or more

were not uncommon. Although the trend soon fizzled and military planners

looked to maneuverability and stealth for survival, the military has recently

shown renewed interest in hypersonic flight. For example, many have

conjectured about the existence of a Mach 5 spy plane, the Aurora, that may

be under development or perhaps already flying. If so, the Aurora may be a

scramjet-powered design similar to the X-30 and X-43 research vehicles.More

recently, Northrop Grumman has unveiled a concept for a hypersonic bomber

designed using waverider principles.

Cruise Missiles: Though developing a man-rated hypersonic vehicle like

those described above will likely require decades of work and enormous cost,

militaries around the world will likely have hypersonic cruise missiles

entering service by 2015. Most current concepts for high-speed missiles are

simple cylinders with no relation to waveriders.

RECENT PROGRESS

In recent years, significant progress has been made in the development of

hypersonic technology, particularly in the field of scramjet engines. While

American efforts are probably the best funded, the first to demonstrate a

scramjet working in an atmospheric test was a shoestring project by an

Australian team at the University of Queensland. The university's HyShot

project demonstrated scramjet combustion in 2002. This demonstration was

somewhat limited, however; while the scramjet engine worked effectively and

demonstrated supersonic combustion in action, the engine was not designed to

provide thrust to propel a craft.

The US Air Force and Pratt and Whitney have cooperated on the Hypersonic

Technology (HyTECH) scramjet engine, which has now been demonstrated in

a wind-tunnel environment. NASA's Marshall Space Propulsion Center has

introduced an Integrated Systems Test of an Air-Breathing Rocket (ISTAR)

program, prompting Pratt & Whitney, Aerojet, and Rocketdyne to join forces

for development.

The most advanced US hypersonics program is the US$250 million NASA

Langley Hyper-X X-43A effort, which flew small test vehicles to demonstrate

hydrogen-fueled scramjet engines. NASA is worked with contractors Boeing,

Microcraft, and the General Applied Science Laboratory (GASL) on the

project.

The NASA Langley, Marshall, and Glenn Centers are now all heavily

engaged in hypersonic propulsion studies. The Glenn Center is taking

leadership on a Mach 4 turbine engine of interest to the USAF. As for the

X-43A Hyper-X, three follow-on projects are now under consideration.

CONCLUSION

Imagine a jet engine that doesn't pollute the atmosphere, flies more than five

times the speed of sound and carry more pay load.

This can be made into reality using Scramjet Engines that is powered by

oxygen it scoops out of the air as it flies.

It will take years of work before scramjets are available for practical uses,

but they could eventually revolutionize space launches and commercial

flights.

Therfore Scramjets are truly the future of flight.

14012013121404-scramjet-engine

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