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Jet Propulsion

Lecture - 28

Ujjwal K Saha, Ph. D.Department of Mechanical Engineering

Indian Institute of Technology Guwahati

Prepared underQIP-CD Cell Project

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Liquid Propellant Rockets-Space

Jet velocity: 2000 - 3500m/s.

Highest thrust, can be throttled.

Long sustained flight (5mins+). Ariane 5

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Liquid Propellant Rocket for GW

• Jet velocity: 2000-3500 m/s.

• Highest thrust/weight, can be throttled.

• Short and medium range (< 50 km).

• Low signature plume. Lance

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Basic Operating Features

• Fuel and oxidant tanked separately and delivered to combustion chamber at specific rates and pressures.

• Propellant flowrates (and hence thrust) variable upon demand.

• Disadvantages compared with solid propellant rockets:– increased complication;– Storage problems (usually LOX & LH2 which must be

maintained at very low temperatures);– more costly;– reduced reliability.

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Impart high velocity to propel a vehicle along its flight path.

Booster and Upper stages of launch vehicles and large missiles - (Boost Propulsion)(Boost Propulsion).

F=4500 N to 8 x 106 N; High Specific Impulse.

No. of Thrust Chambers/engine = 1 to 4. Firing Duration = 5-40 secs.

Chamber Pressure = 2.4 to 21 Mpa.

Cryogenic and Storable Liquids.

Attitude control, trajectory corrections, space maneuvers.

Spacecrafts, Satellites,Space rendevous – (Reaction (Reaction Control Systems)Control Systems).

F=0.001 N to 4500 N. Low specific Impulse.

No. of Thrust Chambers/engine = 4 to 24. Firing Duration = 0.02 secs.

Chamber Pressure = 0.14 to 2.1 Mpa.

Stored Cold Gas /Liquids.

Primary Propulsion Auxiliary Propulsion

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Service:Service:Single FlightReusable type (SSME)Restartable type (RCS)

Stage:Stage:Upper StageBooster Stage

Feed System:Feed System:Gas Pressure Feed System (RCS)Turbo-pump Feed System (BP)

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Solid/Liquid Rockets

Solid Fuel

Liquid Fuel (turbo pump fed)

Liquid Fuel (pressure fed)

oxidizer

fuel

pressurant

Turbo pump

Thrustchamber

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Propellant: A propellant consists of a fuel and an oxidizer. A fuel is a substance which burns when combined with oxygen producing gas for propulsion. An oxidizer is an agent that releases oxygen for combination with a fuel. Most rocket engines use chemical propellants, which can be classified as solid propellantsliquid propellants, ,

hybrid propellantsgelled propellants, , or gaseous propellants depending on their physical state.

Liquid propellants can be further subdivided into monopropellantsbipropellants and . In an ion

propulsion system the propellant particles are first ionized and then accelerated to yield a high-speed exhaust. The gauge for rating the efficiency of rocket propellants is specific impulse.

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Three main categories of liquid propellants may be distinguished:

•petroleum-based•hypergolic•cryogenic

Additionally, liquid propellants may be classed as bipropellants (in which a liquid fuel and a liquid oxidizer are stored separately) or monopropellants.

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1. Monopropellant: Oxidizers and fuel both are in a single substance. A monopropellant decomposes into a hot gas when an appropriate catalyst is introduced. It may be a mixture of several compounds (HAN), or it may be a homogeneous material like H2O2, N2H4.

HAN (hydroxyl ammonium nitrate): A relatively new, synthetic, rocket fuel; chemical formula NH2OH+NO3. It has the potential to be used both as a liquid monopropellant and an ingredient in solid propellants.

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Examples

Oxidizers: LOX, H2O2(Conc.), HNO3 (RFNA, WFNA), N2O4.

Fuels: RP-1, LH2,N2H4 (MMH, UDMH), Alcohol.

2. Bipropellant: Bipropellants are commonly used in liquid-propellant rocket engines, where the fuel and the oxidizer are held separate prior to combustion.

There are many examples, including RP-1 (akerosine-containing mixture) and liquid oxygen(used by the Atlas family), and liquid hydrogenand liquid oxygen (used by the Space Shuttle).

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Liquid Hydrogen: in its liquid state, used as a cryogenic rocket fuel; hydrogen gas turns to liquid under standard atmospheric pressure at -262.9°C. When oxidized by liquid oxygen, liquid hydrogen delivers about 40% more thrust per unit mass than other liquid fuels, such as kerosene. Molecular weight: 2.016; density: 0.071 g/ml. Commonly referred to in rocketry as LH2.

Petroleum-based Propellant: A type of liquid propellantin which the fuel is refined from crude oil and consists of a mixture of complex hydrocarbons, i.e. organic compounds containing only carbon and hydrogen. The petroleum used as rocket fuel is kerosene, or a type of highly refined kerosene known as RP-1. RP-1 is a kerosene fraction, obtained from crude oil with a high napthene content which is subjected to further treatment, including acid washing and sulfur dioxide extraction.

Fuels

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Hydrazine (N2H4): A clear, highly toxic, nitrogen/hydrogen compound with a fishy smell. It is used as a liquid rocket fuel,both as a monopropellant, especially in attitude control thrusters, and as a bipropellant. As a monopropellant in catalytic decomposition engines, it is ignited by passing it over a heated catalyst (alumina pellets impregnated with iridium) that decomposes the fuel and produces ammonia, nitrogen, and hydrogen exhaust gases. The decomposition of hydrazine produces temperatures of about 1700°F and a specific impulse of 230-240 seconds. As a bipropellant it is also a hypergolic propellant used, for example, in the second stage of the Titan family of launch vehicles in a 50% hydrazine / 50% UDMH mixture known as Aerozine 50.

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UDMH: A hypergolic liquid rocket fuel derived from hydrazine. It has the chemical formula (CH3)2NHH2. UDMH is often used instead of, or in mixtures with, hydrazine because it improves stability, especially at higher temperatures. UDMH is employed by many Russian, European, and Chinese rockets. The Titan family of launch vehicles and the second stage of the Delta use a fuel called Aerozine 50, which is a mixture of 50% UDMH and 50% hydrazine.

MMH: A clear, colorless, hygroscopic liquid, with the chemical formula CH3NHNH2, that is derived from hydrazine. MMH is used as a liquid rocket fuel, with nitrogenhypergolictetroxide as an oxidizer, in the orbital maneuvering system (OMS) and reaction control system (RCS) of the Space Shuttle Orbiter. The specific impulse of the MMH/N2O4combination in the Space Shuttle orbiter ranges from 260-280 seconds in the RCS, to 313 seconds in the OMS. The higher efficiency of the OMS system is attributed to higher expansion ratios in the nozzles and higher pressures in the combustion chambers.

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Liquid Oxygen: in its liquid state, used as the oxidizer in many liquid-propellant rocket engines. Oxygen gas turns to liquid under standard atmospheric pressure at -183°C. Molecular weight: 32; density: 1.141 g/ml. Commonly referred to in rocketry as LOX.

Nitric acid (HNO3): A commonly used oxidizer in liquid-propellant rocket engines between 1940 and 1965. It most often took the form of RFNA (red fuming nitric acid), containing 5-20% dissolved nitrogen dioxide. Compared to concentrated nitric acid (also known as white fuming nitric acid), RFNA is more energetic and more stable to store, but produces poisonous red-brown fumes. Because nitric acid is normally highly corrosive it can only be stored and piped by a few materials such as stainless steel. However, the addition of a small concentration of fluoride ions inhibits the corrosiveaction and gives a form known as IRFNA (inhibited red fuming nitric acid). Like nitrogen tetroxide, it is hypergolic (reacts upon contact with) hydrazine, MMH UDMHand .

Oxidizers

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Nitrogen tetroxide (N2O4): A yellow-brown liquid that is among the most common storable oxidizers used by liquid-propellant rocket engines today. Like nitric acid, it is hypergolic (reacts upon contact with) hydrazine MMH, (monomethyl hydrazine), and UDMH (unsymmetricaldimethyl hydrazine). It is used, for example, with MMH in the Space Shuttle orbital maneuvering system. Although it can be stored indefinitely in sealed containers, its liquid temperature range is narrow and it is easily frozen or vaporized.

Hydrogen Peroxide (H2O2): A highly oxidizing compound of hydrogen oxygenand . H2O2 is colorless and caustic to the skin. Pure hydrogen peroxide is stable, but the slightest impurity will enhance decomposition, often violently, liberating oxygen. Concentrated solutions of hydrogen peroxide are highly corrosive and toxic. H2O2 is used as a bleach and a a deodorizer. Molecular weight: 34.02 g/mol. Hydrogen peroxide is dangerous to handle and easily decomposes, making it difficult to store.

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3. Hypergolic Propellant: A form of liquid propellant in which the fuel ignites spontaneously upon contact with an oxidizer, thereby eliminating the need for an ignition system. The easy start and restart capability of hypergolicsmake them ideal for spacecraft maneuvering systems.

Also, since hypergolics remain liquid at normal temperatures, they don't pose the storage problems of cryogenic propellants. On the debit side, hypergolics are highly toxic and must be handled with extreme care. Hypergolic fuels commonly include hydrazine, monomethylhydrazine (MMH), and unsymmetrical dimethyl hydrazine(UDMH). The oxidizer is typically nitrogen tetroxide (N2O4) or nitric acid (HNO3).

4. Anergolic/Non-hypergolic Propellant A propellant in which the liquid fuel and liquid oxidizer do not burn spontaneously when they come into contact. Familiar examples are: Liquid oxygen and Ethanol, WFNA and jet engine fuel, and LOX-LH2 combination.

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5. Cryogenic Propellant: A form of liquid propellantfor rocket engines that must be kept at very low temperatures to remain liquid. The common examples are LH2 and LOX. Cryogenic propellants require special insulated containers and vents to allow gas from the evaporating liquids to escape. The liquid fuel and oxidizer are pumped from the storage tanks to an expansion chamber and injected into the combustion chamber where they are mixed and ignited by a flame or spark.

Because of the low temperatures of cryogenic propellants, they are difficult to store over long periods of time. For this reason, they are less desirable for use in military rockets which must be kept launch ready for months at a time. Also, liquid hydrogen has a very low density (0.59 pounds per gallon) and, therefore, requires a storage volume many times greater than other fuels. Despite these drawbacks, the high efficiency of liquid hydrogen/liquid oxygen makes these problems worth coping with when reaction time and storability are not too critical. Liquid hydrogen delivers a specific impulse about 40% higher than other rocket fuels.

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PROPERTIES OF LIQUID ROCKET PROPELLANTS

compound chemicalformula

molecularweight density melting

pointboilingpoint

liquid oxygen O2 32.00 1.141 g/ml -218.8oC -183.0oC

nitrogen tetroxide N2O4 92.01 1.45 g/ml -9.3oC 21.15oC

nitric acid HNO3 63.01 1.55 g/ml -41.6oC 83oC

liquid hydrogen H2 2.016 0.071 g/ml -259.3oC -252.9oC

hydrazine N2H4 32.05 1.004 g/ml 1.4oC 113.5oC

methyl hydrazine CH3NHNH2 46.07 0.866 g/ml -52.4oC 87.5oC

dimethyl hydrazine (CH3)2NNH2 60.10 0.791 g/ml -58oC 63.9oC

dodecane (kerosene) C12H26 170.34 0.749 g/ml -9.6oC 216.3oC

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Mono and Bipropellants

• Bipropellant Liquid - Energy from chemical reaction of fuel and oxidizer

Examples: – LOX/kerosene (Ispv ≈ 330 seconds)– LOX/hydrogen (Ispv ≈ 450 seconds)– Nitrogen tetroxide/hydrazine (Ispv ≈ 320 seconds)

• Monopropellant Liquid - Energy from chemical decomposition of a single fluid

Examples: – Hydrazine (Ispv ≈ 230 seconds)– Hydrogen peroxide (Ispv ≈ 150 seconds)

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6. Gelled Propellant: A rocket propellant that has additives to make it thixotropic (dynamic viscosity decreases with time for which shearing forces are applied). This means it has the consistency of jelly when at rest but can be made to move as a liquid through pipes, valves, and injectors when adequate shear stress is applied. It has got no spillage/leakage, no sloshing problems, and can be stored for about 10 years. Experimental rocket engines have shown gelled propellants to be generally safer than liquid propellants, yet be capable of performing well.

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7. Gaseous Propellant: A working substance used in a reaction control system. Nitrogen, argon, krypton, dry air, and Freon-14 have all been employed in spacecraft.

7a. Cold Gas Jets: Methane, Helium, Nitrogen, Argon, Krypton, dry air, and Freon-14 are stored under high pressure. Specific impulse ranges from 50 – 120 secs, with low thrust upto 10 N. Used in small Satellites/Roll Control.

7b. Warm Gas Jets: System uses an inert gas with an electric heater/or a monopropellant (N2H4) which is catalytically or thermally decomposed. Gives high specific impulse of 100-250 secs.

7c. Bipropellant System: Sometimes, a combination of N2O4 and MMH is used. Gives specific impulse of 220-325 secs.

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Cold Gas Systems

• Cold Gas Systems: Involves the expulsion of high pressure gas

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A good liquid propellant is one with a high specific impulse. This implies a high combustion temperature and exhaust gases with small molecular weights.

Density of the propellant also plays an important role as a lower density propellant requires a larger storage tank, therebyincreasing the mass of the launch vehicle.

A propellant with a low storage temperature, i.e. a cryogenic,requires thermal insulation, thus further increasing the mass ofthe launcher.

The toxicity of the propellant yet another consideration. There are safety hazards in handling, transporting, and storing highly toxic compounds.

Also, some propellants are very corrosive, however, materials that are resistant to certain propellants have been identified for use in rocket construction.

Some Points

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Liquid Propellant Rocket Enginescan burn many fuels

fuel tank AND oxidizer tank25% more thrust than solidreadily available fuellow combustion temperaturecontrolled rate of fuel flowliquids unaffected by temp/humiditylimitations

Limitations- intricate- corrosive- fueling time too long for defense- bulky - low density

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References1. Hill, P.G., and Peterson, C.R., (1992), Mechanics

and Thermodynamics of Propulsion, Addison Wesley.

2. Oates, G.C., (1988), Aerothermodynamics of Gas Turbine and Rocket Propulsion, AIAA, New York.

3. M.J.L.Turner, (2000), Rocket and Spacecraft Propulsion, Springer.

4. Sutton, G.P. and Biblarz, O., (2001), Rocket Propulsion Elements, John Wiley & Sons.

5. Zucrow, M.J., (1958), Aircraft and Missile Propulsion, Vol. II, John Wiley.

6. Barrere, M., Jaumotte, A., Veubeke, B., and Vandenkerckhove, J., (1960), Rocket Propulsion, Elsevier.

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