VISVESVARAYA TECHNOLOGICAL UNIVERSITY

BELGAUM- 590 018

PAPER PRESENTATION ON

Cryogenic Rocket Engines

Submitted By :

KIRAN S SANKANAGOUDAR & SANDEEP P GAONKAR

kskskiran@gmail.com pgsandeep3@gmail.com

Bachelor of Mechanical Engineering

DEPARTMENT OF MECHANICAL ENGINEERING

SRI TARALABALU JAGADGURU INSTITUTE OF TECHNOLOGY

RANEBENNUR- 581 115

Abstract Cryogenics is a branch of Thermal Engineering that deals with production and maintenance of very low temperatures for

specific purposes. We discuss about the Definition, Application of Cryogenics, Cryogenic Propellants, Production of Cryogenic Propellants, Storage, Utilization, Safety and Cryo Engine specifications used in Rockets. In brief, we are introducing the concept of cryogenics and its technology considering Propellants as the basic application. Cryogenics is a new branch of engineering under Refrigeration, which has a vast area of application as we come to know about each under the discussion. It is basically about the liquifaction of the gases (permanent gases such as Hydrogen, Oxygen, Nitrogen etc.), which have boiling points well below the logical

dividing line of –1800C (93.15K). Hence, all substances that deal with maintenance of very low temperatures, below the dividing line are termed as cryogenics

Definition:

Cryogenics by definition is that branch of Physics or Engineering that deal with the substances that need to be maintained at temperatures below that of

the logical dividing line of –1800C (93.15K). It is the recent technological advancement in the field of Medicine, Aerospace, Metallurgy and Preservation of biological objects.

INTRODUCTIONCryogenics originated from two Greek words “kyros” which means cold orfreezing and “genes” which means born or produced. Cryogenics is the study of verylow temperatures or the production of the same. Liquefied gases like liquid nitrogen andliquid oxygen are used in many cryogenic applications. Liquid nitrogen is the mostcommonly used element in cryogenics and is legally purchasable around the world.

Liquid helium is also commonly used and allows for the lowest temperatures to bereached. These gases can be stored on large tanks called Dewar tanks, named after

James Dewar, who first liquefied hydrogen, or in giant tanks used for commercialapplications.The field of cryogenics advanced when during world war two, when metals werefrozen to low temperatures showed more wear resistance. In 1966, a company wasformed, called Cyro-Tech, which experimented with the possibility of using cryogenic tempering instead of Heat Treating, for increasing the life of metal tools.The engine components are also cooled so the fuel doesn't boil to a gas in thelines that feed the engine. The thrust comes from the rapid expansion from liquid to gaswith the gas emerging from the motor at very high speed. The energy needed to heatthe fuels comes from burning them, once they are gasses. Cryogenic engines are thehighest performing rocket motors. One disadvantage is that the fuel tanks tend to bebulky and require heavy insulation to store the propellant. Their high fuel efficiency,however, outweighs this disadvantage.The Space Shuttle's main engines used for liftoff are cryogenic engines. TheShuttle's smaller thrusters for orbital maneuvering use non-cryogenic hypergolic fuels, which are compact and are stored at warm temperatures. Currently, only the UnitedStates, Russia, China, France, Japan and India have mastered cryogenic rockettechnology. All the current Rockets run on Liquid-propellant rockets. The first operationalcryogenic rocket engine was the 1961 NASA design the RL-10 LOX LH2 rocket engine, which was used in the Saturn 1 rocket employed in the early stages of the Apollo moon landing program.The major components of a cryogenic rocket engine are:

the thrust chamber or combustion chamber

pyrotechnic igniter fuel injector fuel turbo-pumps gas turbine cryo valves Regulators The fuel tanks rocket engine nozzle

Among them, the combustion chamber & the nozzle are the main components of

the rocket engine.

SPACE PROPULSIION SYSTEM Spacecraft propulsion is any method used to accelerate spacecraft and artificialsatellites. There are many different methods. Each method has drawbacks andadvantages, and spacecraft propulsion is an active area of research. However, mostspacecraft today are propelled by forcing a gas from the back/rear of the vehicle at veryhigh speed through a supersonic de Laval nozzle. This sort of engine is called a rocketengine. All current spacecraft use chemical rockets (bipropellant or solid-fuel) for launch,though some have used air-breathing engines on their first stage. Most satellites havesimple reliable chemical thrusters. Soviet bloc satellites have used electric propulsionfor decades, and newer Western geo-orbiting spacecraft are starting to use them fornorth-south station keeping. Interplanetary vehicles mostly use chemical rockets aswell, although a few have used ion thrusters to great success.

Classification of Space Propulsion System

Storage: For small storage of cryogenic substances Dewar Flasks are used. (1.8m x 91.5cm). They are named after James Dewar who was the pioneer in liquefaction of Hydrogen. For larger quantities special insulators need to be employed. One of which is explained below.

Many workers achieve this by the use of liquid nitrogen (at –196ºC), which is a dangerous medium to work in as the 700X expansion on heating of the material in an enclosed space can lead to explosions. We therefore recommend that samples be stored in the gas phase above the nitrogen (-178 to –150ºC) to be absolutely safe. In this state the temperature is well below the level required to keep the material in good condition.

There are many types of Dewars used for the same purpose of storage. From Horizontal to vertical, from open hoopers to closed, we have all types of Dewars as per the industrial requirements.

Cooling Requirement of

Cryogenics:

It can be achieved by mainly three methods, By Transfer of HeatBy External WorkBy Isenthalpic Expansion

By transfer of heat:

Substances can be cooled to cryogenic temperatures by transferring heat from a cold gas stream by using flat plate heat exchangers. A matrix of flat plate and

corrugated fins can be used for the construction of the Heat exchanger.

By External Work:

Adiabatic expansion of a gas in a turbine or reverse engineering as in case of a reciprocating engine can be applied to produce the required low temperature. Thus as it explains itself, we need a refrigerant which has a boiling point lesser than the required temperature as a working fluid to accomplish the same.

Isenthalpic Expansion:

We are familiar with the Joule-Thompson effect. The working temperature and pressure must be well within the Inversion curve of the specified gas. However, this process is highly ideal, and its practicably too far from reality.

Expansion system can be applied by the use of a Brayton cycle engine working under the reverse. A Turbo-Expander can also be used to accomplish the above same. A Linde's valve can be used for higher efficiency in cooling. It employs a Heat Exchanger, a Joule-Thompson valve and a compressor to achieve the cooling effect. Also a Claude cycle can be applied for the above same.

ROCKET ENGINE POWER CYCLESGas pressure feed system A simple pressurized feed system is shown schematically below. It consists of ahigh-pressure gas tank, a gas starting valve, a pressure regulator, propellant tanks,propellant valves, and feed lines. Additional components, such as filling and drainingprovisions, check valves, filters, flexible elastic bladders for separating the liquid fromthe pressurizing gas, and pressure sensors or gauges, are also often incorporated. Afterall tanks are filled, the high-pressure gas valve is remotely actuated and admits gasthrough the pressure regulator at a constant pressure to the propellant tanks. The checkvalves prevent mixing of the oxidizer with the fuel when the unit is not in an rightposition. The propellants are fed to the thrust chamber by opening valves. When the

propellants are completely consumed, the pressurizing gas can also scavenge andclean lines and valves of much of the liquid propellant residue. The variations in thissystem, such as the combination of several valves into one or the elimination andaddition of certain components, depend to a large extent on the application. If a unit isto be used over and over, such as space-maneuver rocket, it will include severaladditional features such as, possibly, a thrust-regulating device and a tank level gauge.

Gas-Generator CycleThe gas-generator cycle taps off a small amount of fuel and oxidizer from themain flow to feed a burner called a gas generator. The hot gas from this generatorpasses through a turbine to generate power for the pumps that send propellants to thecombustion chamber. The hot gas is then either dumped overboard or sent into themain nozzle downstream. Increasing the flow of propellants into the gas generatorincreases the speed of the turbine, which increases the flow of propellants into the main combustion chamber (and hence, the amount of thrust produced). The gas generator must burn propellants at a less-than-optimal mixture ratio to keep the temperature low for the turbine blades. Thus, the cycle is appropriate for moderate power requirements but not high-power systems, which would have to divert a large portion of the main flow to the less efficient gas-generator flow.

Staged Combustion Cycle

In a staged combustion cycle, the propellants are burned in stages. Like the gasgeneratorcycle, this cycle also has a burner, called a preburner, to generate gas for aturbine. The pre-burner taps off and burn a small amount of one propellant and a large amount of the other, producing an oxidizer-rich or fuel-rich hot gas mixture that is mostly unburned vaporized propellant. This hot gas is then passed through the turbine, injectedinto the main chamber, and burned again with the remaining propellants. The advantage over the gas-generator cycle is that all of the propellants are burned at the optimal mixture ratio in the main chamber and no flow is dumped overboard. The staged combustion cycle is often used for high-power applications. The higher the chamber pressure, the smaller and lighter the engine can be to produce the same thrust.Development cost for this cycle is higher because the high pressures complicate thedevelopment process.

COMBUSTION IN THRUST CHAMBERThe thrust chamber is the key subassembly of a rocket engine. Here the liquidpropellants are metered, injected, atomized, vaporized, mixed, and burned to form hotreaction gas products, which in turn are accelerated and ejected at high velocity. Arocket thrust chamber assembly has an injector, a combustion chamber, a supersonicnozzle, and mounting provisions. All have to withstand the extreme heat of combustionand the various forces, including the transmission of the thrust force to the vehicle.There also is an ignition system if non-spontaneously ignitable propellants are used.

FUEL INJECTIONThe functions of the injector are similar to those of a carburetor of an internalcombustion engine. The injector has to introduce and meter the flow of liquid propellantsto the combustion chamber, cause the liquids to be broken up into small droplets (aprocess called atomization), and distribute and mix the propellants in such a mannerthat a correctly proportioned mixture of fuel and oxidizer will result, with uniformpropellant mass flow and composition over the chamber cross section. This has beenaccomplished with different types of injector designs and elements.The injection hole pattern on the face of the injector is closely related to theinternal manifolds or feed passages within the injector. These provide for the distributionof the propellant from the injector inlet to all the injection holes.Dribbling results in afterburning, which is an inefficient irregular combustion thatgives a little "cutoff" thrust after valve closing. For applications with very accurateterminal vehicle velocity requirements, the cutoff impulse has to be very small andreproducible and often valves are built into the injector to minimize passage volume.Impinging-stream-type, multiple-hole injectors are commonly used with oxygenhydrocarbonand storable propellants. For unlike doublet patterns the propellants are injected through a number of separate small holes in such a manner that the fuel andoxidizer streams impinge upon each other. Impingement forms thin liquid fans and aidsatomization of the liquids into droplets, also aiding distribution. The two liquid streamsthen form a fan which breaks up into droplets.

pressure drop. This type of variable area concentric tube injector was used on thedescent engine of the Lunar Excursion Module and throttled over a 10:1 range of flowwith only a very small change in mixture ratio.The coaxial hollow post injector has been used for liquid oxygen and gaseous hydrogen injectors by most domestic and foreign rocket designers. It works well whenthe liquid hydrogen has absorbed heat from cooling jackets and has been gasified. Thisgasified hydrogen flows at high speed (typically 330 m/sec or 1000 ft/sec); the liquidoxygen flows far more slowly (usually at less than 33 m/sec or 100 ft/sec) and thedifferential velocity causes a shear action, which helps to break up the oxygen streaminto small droplets. The injector has a multiplicity of these coaxial posts on its face.

Primary Ignition begins at the time of deposition of the

energy into the shear layer and ends when

the flame front has reached the outer limit of the shear layer.

starts interaction with the recirculation zone.

phase typically lasts about half a millisecond.

it is characterised by a slight but distinct downstream movement of the flame .

The flame velocity more or less depends on the pre-mixedness of the shear layer only.

Flame Propagation This phase corresponds to the time

span for the flame reaching the edge of theshear layer, expands into in the recirculation zone and propagates until it has consumed all the premixed propellants.

This period lasts between 0.1 and 2 ms.

It is characterised by an upstream movement of the upstream flame front until it reaches a minimum distance from the injector face plate.

It is accompanied by a strong rise of the flame intensity and by a peak in the combustion chamber pressure.

The duration of this phase as well as the pressure and emission behaviour during this phase depend strongly on the global characteristics of the stationary cold flow before ignition.

Flame Lift Off phase starts when the upstream

flame front begins to move downstream awayfrom the injector because all premixed propellants in the recirculation zone have been consumed until it reaches a maximum distance.

This period lasts between 1 and 5 ms.

The emission of the flame is less intense showing that the chemical activity has decreased.

The position where the movement of the upstream flame front comes to an end, the characteristic times of convection and flame propagation are balanced.

Flame Anchoring. This period lasts from 20 ms to more

than 50 ms, depending on the injection condition.

It begins when the flame starts to move a second time upstream to injector face plate and ends when the flame has reached stationary conditions.

During this phase the flame propagates upstream only in the shear layer .

Same as flame lift-off phase the vaporisation is enhanced by the hot products which are entrained into the shear layer through the recirculation zone.

This local flame velocity is depending on the upstream LOX-evaporation rates, i.e., the available gaseous O2, mixing of O2 and H2, hot products and radicals in the shear layer.

At the end of this phase, combustion chamber pressure and emission intensity are constant.

DIFFERENT TYPES OF CRYOGENIC ENGINES

HM-7B Rocket EngineHM-7 cryogenic propellant rocket engine has been used as an upper stageengine on all versions of the Ariane launcher. The more powerful HM-7B version wasused on Ariane's 2, 3 and 4 and is also used on the ESC-A cryogenic upper stage ofAriane 5. Important principles used in the HM-7 combustion chamber were adopted byNASA under license and it is this technology that formed the basis of today's US spacethe first launch of Ariane 1 in December 1979.

300 N Cryogenic Engine:

Used as a main engine for oorbital insertion, orbital transfer, orbital, and interplanetary applications includingupper stagekick stagevernier stagetransfer stage The thrust chamber and throat region of the engine are regenerativecooled using hydrogen propellant.

being pressure fed, the engine does not requires any turbo pump, with its associated complexity.

Vulcain Rocket Engine

The Vulcain engines are gas-generator cycle cryogenic rocket engines fed with liquid oxygen and liquid hydrogen.They feature regenerative cooling through a tube wall design, and the Vulcain 2introduced a particular film cooling for the lower part of the nozzle, where exhaust gasfrom the turbine is re-injected in the engine The engine operating time is 600 s in both configurations.The coaxial injector elements cause the LOX and LH2 propellants to be mixedtogether. LOX is injected at the centre of the injector, around which the LH2 is injected.These propellants are mainly atomized and mixed by shear forces generated by thevelocity differences between LOX and LH2. The final acceleration of hot gases, up tosupersonic velocities, is achieved by gas expansion in the nozzle extension, therebyincreasing the thrust.

Applications: main engine of the Ariane 5

cryogenic first stage (EPC).

VINCI Rocket Engine: Vinci is a European Space Agency cryogenic rocket engine currently under development. It is designed to power the new upper stage of Ariane 5, ESC-B, and will be the first European re-ignitable cryogenic upper stage engine, raising the launcher's GTO performances to 12 t. Vinci is an expander cycle rocket engine fed with liquid hydrogen and liquid oxygen. Its biggest improvement from its predecessor, the HM-7 is the capability of restarting up to five times. It is also the first European expander cycle engine, removing the need for a gas generator to drive the fuel and oxydizer pumps. It features a carbon ceramic extendable nozzle in order to have a large, 2.15 m diameter nozzle extension with minimum length: the retracted nozzle part is deployed only after the upper stage separates from the rest of the rocket; after extension, the engine's overall length increases from 2.3 m to 4.2 m.

ADVANTAGES:

High Energy per unit mass: Propellants like oxygen and hydrogen in liquid form give very high amounts of energy per unit mass due to which the amount of fuel to be carried aboard the rockets decreases.

Clean Fuels: Hydrogen and oxygen are extremely clean fuels. When they combine, they give out only water. This water is thrown out of the nozzle in form of very hot vapour. Thus the rocket is nothing but a high burning steam engine Economical: Use of oxygen and hydrogen as fuels is very economical, as liquid oxygen costs less than gasoline.

DISADVANTAGES Boil off Rate Highly reactive gases Leakage Hydrogen Embrittlement Zero Gravity conditions

Merits & Demerits of cryogenic:

Some of the credits to cryogenics is that when safely used, it can be very helpful to mankind, as given in the applications part, from medicine to engineering, cryo liquids are employed totally. It has a wide area of application. The propellant mixture of cryogenic substances is very clean and needs to be de-activated at the right times before it harms anyone. Hence, all the merits can be analyzed from the applications point of view.

The main disadvantage of these propellants is their very low temperature. They must be protected from heat so as to prevent boiling off of gases. When liquid propellants are stored at temperatures above their boiling point they vaporize. If these vapors are contained in a tank, then the pressure increases with temperature. Thus resulting in an explosion. This has to be prevented.

One of the most major concerns is leakage. At cryogenic temperatures, which are roughly below 150 degrees Kelvin or equivalently (-190) degrees Fahrenheit, the seals of the container used for storing the propellants lose the ability to maintain a seal properly. Hydrogen, being the smallest element, has a tendency to leak past seals or materials.

Hydrogen can burst into flames whenever its concentration is approximately 4% to 96%. It is hence necessary to ensure that hydrogen leak rate is minimal and does not present a

hazard. The compartments where hydrogen gas may exist in case of a leak must be made safe, so that the hydrogen buildup does not cause a hazardous condition.

Safety:

Cryogenic substances have their own hazards when compared with their applications. The workers need to be protected from contact with the cryogenic gases as prolonged exposure can cause Frostbite. As in case of burns with regard to flames, even cryogenic substances can cause burns on the skin. At cryogenic temperatures many materials behave in ways unfamiliar under ordinary conditions. Mercury solidifies and rubber becomes as brittle as glass. The specific heats of gases and solids decrease in a way that confirms the predictions of quantum theory. The vapors and gases released from cryogenic liquids also remain very cold. They often condense the moisture in air, creating a highly visible fog. Cryogenic gases can cause Asphyxiation which is analogous with the phenomenon of reduction of oxygen percentage (less than 18%).

Utilization:

It is used as propellants for many space shuttles and rockets. To name a few we have, Airiane, GSLV Mk I/II/III, NASA’s space shuttles, etc., we consider GSLV Mk II and III as the examples. The third stage of the rocket in the GSLV Mk II is the GS3 or the cryogenic stage that employs LH2 & LOX as propellants.

It has a burn out time of 705 seconds and is considered to be most clean among all other propellants. GSLV Mk II has a capability of launching a 2000 kg class satellite into the GTO. While the new advancement the Mk III, has a capability of launching a 4000 kg class

satellite into the GTO or a 10 tones class satellite into the LEO. The Mk III has a cryo stage carrying 25 tones of LH2 & LOX as propellants and is capable of developing 20 tones of thrust (197kN). It employs a TBC engine to develop this huge amount of thrust. The picture shows, the testing of the cryogenic propellant based engine of GSLV Mk II. It is easy to notice that the combustion products produced are hardly visible when compared with other propellants.

CONCLUSION

The area of Cryogenics in Cryogenic Rocket Engines is a vast one and it cannotbe described in a few words. As the world progress new developments are being mademore and more new developments are being made in the field of Rocket Engineering.Now a day cryo propelled rocket engines are having a great demand in the field ofspace exploration. Due to the high specific impulse obtained during the ignition of fuels they are of much demand.

REFERENCES:

Google images and information.

“Rocket propulsion elements” By G. P. Sutton, 7th edition.