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Jet propulsion

From Wikipedia, in a visual modern way
The jet engine of a Boeing 787 Dreamliner.
The jet engine of a Boeing 787 Dreamliner.
A pump-jet on a ferry.
A pump-jet on a ferry.

Jet propulsion is the propulsion of an object in one direction, produced by ejecting a jet of fluid in the opposite direction. By Newton's third law, the moving body is propelled in the opposite direction to the jet. Reaction engines operating on the principle of jet propulsion include the jet engine used for aircraft propulsion, the pump-jet used for marine propulsion, and the rocket engine and plasma thruster used for spacecraft propulsion.

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Propulsion

Propulsion

Propulsion is the generation of force by any combination of pushing or pulling to modify the translational motion of an object, which is typically a rigid body but may also concern a fluid. The term is derived from two Latin words: pro, meaning before or forward; and pellere, meaning to drive. A propulsion system consists of a source of mechanical power, and a propulsor.

Jet (fluid)

Jet (fluid)

A jet is a stream of fluid that is projected into a surrounding medium, usually from some kind of a nozzle, aperture or orifice. Jets can travel long distances without dissipating.

Fluid

Fluid

In physics, a fluid is a liquid, gas, or other material that continuously deforms (flows) under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear force applied to them.

Reaction engine

Reaction engine

A reaction engine is an engine or motor that produces thrust by expelling reaction mass, in accordance with Newton's third law of motion. This law of motion is commonly paraphrased as: "For every action force there is an equal, but opposite, reaction force."

Jet engine

Jet engine

A jet engine is a type of reaction engine, discharging a fast-moving jet of heated gas that generates thrust by jet propulsion. While this broad definition may include rocket, water jet, and hybrid propulsion, the term jet engine typically refers to an internal combustion air-breathing jet engine such as a turbojet, turbofan, ramjet, or pulse jet. In general, jet engines are internal combustion engines.

Pump-jet

Pump-jet

A pump-jet, hydrojet, or water jet is a marine system that produces a jet of water for propulsion. The mechanical arrangement may be a ducted propeller, a centrifugal pump, or a mixed flow pump which is a combination of both centrifugal and axial designs. The design also incorporates an intake to provide water to the pump and a nozzle to direct the flow of water out of the pump.

Marine propulsion

Marine propulsion

Marine propulsion is the mechanism or system used to generate thrust to move a watercraft through water. While paddles and sails are still used on some smaller boats, most modern ships are propelled by mechanical systems consisting of an electric motor or internal combustion engine driving a propeller, or less frequently, in pump-jets, an impeller. Marine engineering is the discipline concerned with the engineering design process of marine propulsion systems.

Rocket engine

Rocket engine

A rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propulsive jet of fluid, usually high-temperature gas. Rocket engines are reaction engines, producing thrust by ejecting mass rearward, in accordance with Newton's third law. Most rocket engines use the combustion of reactive chemicals to supply the necessary energy, but non-combusting forms such as cold gas thrusters and nuclear thermal rockets also exist. Vehicles propelled by rocket engines are commonly called rockets. Rocket vehicles carry their own oxidiser, unlike most combustion engines, so rocket engines can be used in a vacuum to propel spacecraft and ballistic missiles.

Spacecraft propulsion

Spacecraft propulsion

Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. In-space propulsion exclusively deals with propulsion systems used in the vacuum of space and should not be confused with space launch or atmospheric entry.

Physics

Jet propulsion is produced by some reaction engines or animals when thrust is generated by a fast moving jet of fluid in accordance with Newton's laws of motion. It is most effective when the Reynolds number is high—that is, the object being propelled is relatively large and passing through a low-viscosity medium.[1]

In animals, the most efficient jets are pulsed, rather than continuous,[2] at least when the Reynolds number is greater than 6.[3]

Specific impulse

Main article: Specific impulse

Specific impulse (usually abbreviated Isp) is a measure of how effectively a rocket uses propellant or jet engine uses fuel. By definition, it is the total impulse (or change in momentum) delivered per unit of propellant consumed[4] and is dimensionally equivalent to the generated thrust divided by the propellant mass flow rate or weight flow rate.[5] If mass (kilogram, pound-mass, or slug) is used as the unit of propellant, then specific impulse has units of velocity. If weight (newton or pound-force) is used instead, then specific impulse has units of time (seconds). Multiplying flow rate by the standard gravity (g0) converts specific impulse from the mass basis to the weight basis.[5]

A propulsion system with a higher specific impulse uses the mass of the propellant more effectively in creating forward thrust and, in the case of a rocket, less propellant needed for a given delta-v, per the Tsiolkovsky rocket equation.[4][6] In rockets, this means the engine is more effective at gaining altitude, distance, and velocity. This effectiveness is less important in jet engines that employ wings and use outside air for combustion and carry payloads that are much heavier than the propellant.

Specific impulse includes the contribution to impulse provided by external air that has been used for combustion and is exhausted with the spent propellant. Jet engines use outside air, and therefore have a much higher specific impulse than rocket engines. The specific impulse in terms of propellant mass spent has units of distance per time, which is an artificial velocity called the "effective exhaust velocity". This is higher than the actual exhaust velocity because the mass of the combustion air is not being accounted for. Actual and effective exhaust velocity are the same in rocket engines not utilizing air.

Specific impulse is inversely proportional to specific fuel consumption (SFC) by the relationship Isp = 1/(go·SFC) for SFC in kg/(N·s) and Isp = 3600/SFC for SFC in lb/(lbf·hr).

Thrust

From the definition of specific impulse thrust in SI units is:

where Ve is the effective exhaust velocity and is the propellant flow rate.

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Jet (fluid)

Jet (fluid)

A jet is a stream of fluid that is projected into a surrounding medium, usually from some kind of a nozzle, aperture or orifice. Jets can travel long distances without dissipating.

Fluid

Fluid

In physics, a fluid is a liquid, gas, or other material that continuously deforms (flows) under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear force applied to them.

Newton's laws of motion

Newton's laws of motion

Newton's laws of motion are three basic laws of classical mechanics that describe the relationship between the motion of an object and the forces acting on it. These laws can be paraphrased as follows:A body remains at rest, or in motion at a constant speed in a straight line, unless acted upon by a force. When a body is acted upon by a force, the time rate of change of its momentum equals the force. If two bodies exert forces on each other, these forces have the same magnitude but opposite directions.

Jet engine

Jet engine

A jet engine is a type of reaction engine, discharging a fast-moving jet of heated gas that generates thrust by jet propulsion. While this broad definition may include rocket, water jet, and hybrid propulsion, the term jet engine typically refers to an internal combustion air-breathing jet engine such as a turbojet, turbofan, ramjet, or pulse jet. In general, jet engines are internal combustion engines.

Impulse (physics)

Impulse (physics)

In classical mechanics, impulse is the integral of a force, F, over the time interval, t, for which it acts. Since force is a vector quantity, impulse is also a vector quantity. Impulse applied to an object produces an equivalent vector change in its linear momentum, also in the resultant direction. The SI unit of impulse is the newton second (N⋅s), and the dimensionally equivalent unit of momentum is the kilogram meter per second (kg⋅m/s). The corresponding English engineering unit is the pound-second (lbf⋅s), and in the British Gravitational System, the unit is the slug-foot per second (slug⋅ft/s).

Momentum

Momentum

In Newtonian mechanics, momentum is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If m is an object's mass and v is its velocity, then the object's momentum p is :

Propellant

Propellant

A propellant is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the engine that expels the propellant is called a reaction engine. Although technically a propellant is the reaction mass used to create thrust, the term "propellant" is often used to describe a substance which is contains both the reaction mass and the fuel that holds the energy used to accelerate the reaction mass. For example, the term "propellant" is often used in chemical rocket design to describe a combined fuel/propellant, although the propellants should not be confused with the fuel that is used by an engine to produce the energy that expels the propellant. Even though the byproducts of substances used as fuel are also often used as a reaction mass to create the thrust, such as with a chemical rocket engine, propellant and fuel are two distinct concepts.

Dimensional analysis

Dimensional analysis

In engineering and science, dimensional analysis is the analysis of the relationships between different physical quantities by identifying their base quantities and units of measure and tracking these dimensions as calculations or comparisons are performed. The conversion of units from one dimensional unit to another is often easier within the metric or the SI than in others, due to the regular 10-base in all units.

Mass flow rate

Mass flow rate

In physics and engineering, mass flow rate is the mass of a substance which passes per unit of time. Its unit is kilogram per second in SI units, and slug per second or pound per second in US customary units. The common symbol is , although sometimes μ is used.

Mass

Mass

Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementary particles, theoretically with the same amount of matter, have nonetheless different masses. Mass in modern physics has multiple definitions which are conceptually distinct, but physically equivalent. Mass can be experimentally defined as a measure of the body's inertia, meaning the resistance to acceleration when a net force is applied. The object's mass also determines the strength of its gravitational attraction to other bodies.

Kilogram

Kilogram

The kilogram is the base unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially. It means 'one thousand grams'.

Newton (unit)

Newton (unit)

The newton is the unit of force in the International System of Units (SI). It is defined as 1 kg⋅m/s2, the force which gives a mass of 1 kilogram an acceleration of 1 metre per second per second. It is named after Isaac Newton in recognition of his work on classical mechanics, specifically Newton's second law of motion.

Types of reaction engine

Main article: Reaction engine

Reaction engines produce thrust by expelling solid or fluid reaction mass; jet propulsion applies only to engines which use fluid reaction mass.

Jet engine

Main article: Jet engine

A jet engine is a reaction engine which uses ambient air as the working fluid, and converts it to a hot, high-pressure gas which is expanded through one or more nozzles. Two types of jet engine, the turbojet and turbofan, employ axial-flow or centrifugal compressors to raise the pressure before combustion, and turbines to drive the compression. Ramjets operate only at high flight speeds because they omit the compressors and turbines, depending instead on the dynamic pressure generated by the high speed (known as ram compression). Pulse jets also omit the compressors and turbines, but can generate static thrust and have limited maximum speed.

Rocket engine

Main article: Rocket engine

The rocket is capable of operating in the vacuum of space, because it is dependent on the vehicle carrying its own oxidizer instead of using the oxygen in the air, or in the case of a nuclear rocket, heats an inert propellant (such as liquid hydrogen) by forcing it through a nuclear reactor.

Plasma engine

Main article: Plasma propulsion engine

Plasma thrusters accelerate a plasma by electromagnetic means.

Pump-jet

Main article: Pump-jet

The pump-jet, used for marine propulsion, uses water as the working fluid, pressurized by a ducted propeller, centrifugal pump, or a combination of the two.

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Reaction engine

Reaction engine

A reaction engine is an engine or motor that produces thrust by expelling reaction mass, in accordance with Newton's third law of motion. This law of motion is commonly paraphrased as: "For every action force there is an equal, but opposite, reaction force."

Jet engine

Jet engine

A jet engine is a type of reaction engine, discharging a fast-moving jet of heated gas that generates thrust by jet propulsion. While this broad definition may include rocket, water jet, and hybrid propulsion, the term jet engine typically refers to an internal combustion air-breathing jet engine such as a turbojet, turbofan, ramjet, or pulse jet. In general, jet engines are internal combustion engines.

Nozzle

Nozzle

A nozzle is a device designed to control the direction or characteristics of a fluid flow as it exits an enclosed chamber or pipe.

Turbofan

Turbofan

The turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft propulsion. The word "turbofan" is a portmanteau of "turbine" and "fan": the turbo portion refers to a gas turbine engine which achieves mechanical energy from combustion, and the fan, a ducted fan that uses the mechanical energy from the gas turbine to force air rearwards. Thus, whereas all the air taken in by a turbojet passes through the combustion chamber and turbines, in a turbofan some of that air bypasses these components. A turbofan thus can be thought of as a turbojet being used to drive a ducted fan, with both of these contributing to the thrust.

Centrifugal compressor

Centrifugal compressor

Centrifugal compressors, sometimes called impeller compressors or radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery.

Combustor

Combustor

A combustor is a component or area of a gas turbine, ramjet, or scramjet engine where combustion takes place. It is also known as a burner, combustion chamber or flame holder. In a gas turbine engine, the combustor or combustion chamber is fed high-pressure air by the compression system. The combustor then heats this air at constant pressure as the fuel/air mix burns. As it burns the fuel/air mix heats and rapidly expands. The burned mix is exhausted from the combustor through the nozzle guide vanes to the turbine. In the case of a ramjet or scramjet engines, the exhaust is directly fed out through the nozzle.

Ramjet

Ramjet

A ramjet, or athodyd, is a form of airbreathing jet engine that uses the forward motion of the engine to produce thrust. Since it produces no thrust when stationary ramjet-powered vehicles require an assisted take-off like a rocket assist to accelerate it to a speed where it begins to produce thrust. Ramjets work most efficiently at supersonic speeds around Mach 3 and can operate up to speeds of Mach 6.

Dynamic pressure

Dynamic pressure

In fluid dynamics, dynamic pressure is the quantity defined by:

Rocket engine

Rocket engine

A rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propulsive jet of fluid, usually high-temperature gas. Rocket engines are reaction engines, producing thrust by ejecting mass rearward, in accordance with Newton's third law. Most rocket engines use the combustion of reactive chemicals to supply the necessary energy, but non-combusting forms such as cold gas thrusters and nuclear thermal rockets also exist. Vehicles propelled by rocket engines are commonly called rockets. Rocket vehicles carry their own oxidiser, unlike most combustion engines, so rocket engines can be used in a vacuum to propel spacecraft and ballistic missiles.

Spaceflight

Spaceflight

Spaceflight is an application of astronautics to fly spacecraft into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such as satellites in orbit around Earth, but also includes space probes for flights beyond Earth orbit. Such spaceflight operates either by telerobotic or autonomous control. The more complex human spaceflight has been pursued soon after the first orbital satellites and has reached the Moon and permanent human presence in space around Earth, particularly with the use of space stations. Human spaceflight programs include the Soyuz, Shenzhou, the past Apollo Moon landing and the Space Shuttle programs, with currently the International Space Station as the main destination of human spaceflight missions while China's Tiangong Space Station is under construction.

Hydrogen

Hydrogen

Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula H2. It is colorless, odorless, tasteless, non-toxic, and highly combustible. Hydrogen is the most abundant chemical substance in the universe, constituting roughly 75% of all normal matter. Stars such as the Sun are mainly composed of hydrogen in the plasma state. Most of the hydrogen on Earth exists in molecular forms such as water and organic compounds. For the most common isotope of hydrogen each atom has one proton, one electron, and no neutrons.

Nuclear reactor

Nuclear reactor

A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nuclear fission is passed to a working fluid, which in turn runs through steam turbines. These either drive a ship's propellers or turn electrical generators' shafts. Nuclear generated steam in principle can be used for industrial process heat or for district heating. Some reactors are used to produce isotopes for medical and industrial use, or for production of weapons-grade plutonium. As of 2022, the International Atomic Energy Agency reports there are 422 nuclear power reactors and 223 nuclear research reactors in operation around the world.

Jet-propelled animals

Main article: Aquatic locomotion § Jet propulsion

Cephalopods such as squid use jet propulsion for rapid escape from predators; they use other mechanisms for slow swimming. The jet is produced by ejecting water through a siphon, which typically narrows to a small opening to produce the maximum exhalent velocity. The water passes through the gills prior to exhalation, fulfilling the dual purpose of respiration and locomotion.[1] Sea hares (gastropod molluscs) employ a similar method, but without the sophisticated neurological machinery of cephalopods they navigate somewhat more clumsily.[1]

Some teleost fish have also developed jet propulsion, passing water through the gills to supplement fin-driven motion.[7]: 201 

In some dragonfly larvae, jet propulsion is achieved by the expulsion of water from a specialised cavity through the anus. Given the small size of the organism, a great speed is achieved.[8]

Scallops and cardiids,[9] siphonophores,[10] tunicates (such as salps),[11][12] and some jellyfish[13][14][15] also employ jet propulsion. The most efficient jet-propelled organisms are the salps,[11] which use an order of magnitude less energy (per kilogram per metre) than squid.[16]

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Cephalopod

Cephalopod

A cephalopod is any member of the molluscan class Cephalopoda such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot. Fishers sometimes call cephalopods "inkfish", referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology.

Siphon (mollusc)

Siphon (mollusc)

A siphon is an anatomical structure which is part of the body of aquatic molluscs in three classes: Gastropoda, Bivalvia and Cephalopoda.

Dragonfly

Dragonfly

A dragonfly is a flying insect belonging to the infraorder Anisoptera below the order Odonata. About 3,000 extant species of true dragonflies are known. Most are tropical, with fewer species in temperate regions. Loss of wetland habitat threatens dragonfly populations around the world. Adult dragonflies are characterized by a pair of large, multifaceted, compound eyes, two pairs of strong, transparent wings, sometimes with coloured patches, and an elongated body. Many dragonflies have brilliant iridescent or metallic colours produced by structural colouration, making them conspicuous in flight. An adult dragonfly's compound eyes have nearly 24,000 ommatidia each.

Polyorchis

Polyorchis

Polyorchis, or bell jellies, is a genus of hydrozoans in the family Corynidae. They are transparent with red coloration in their internal organs and eye spots around the rim of their bell. The red pigmentation helps them camouflage. They are often found in harbors, marinas, and other calm waters close to shore. They feed on plankton and benthic crustaceans and are found near the sea floor. The bells can reach about 2.25 inches (5 cm).

Source: "Jet propulsion", Wikipedia, Wikimedia Foundation, (2023, February 26th), https://en.wikipedia.org/wiki/Jet_propulsion.

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Further Reading

Jet engine

Rocket

Spacecraft propulsion

Nuclear thermal rocket

Antimatter rocket

Rocket engine

Laser propulsion

Plasma propulsion engine

Rocket engine nozzle

Spacecraft electric propulsion

Rocket propellant
See also
References
  1. ^ a b c Packard, A. (1972). "Cephalopods and Fish: the Limits of Convergence". Biological Reviews. 47 (2): 241–307. doi:10.1111/j.1469-185X.1972.tb00975.x. S2CID 85088231.
  2. ^ Sutherland, K. R.; Madin, L. P. (2010). "Comparative jet wake structure and swimming performance of salps" (PDF). Journal of Experimental Biology. 213 (Pt 17): 2967–75. doi:10.1242/jeb.041962. PMID 20709925.
  3. ^ Dabiri, J. O.; Gharib, M. (2005). "The role of optimal vortex formation in biological fluid transport". Proceedings of the Royal Society B: Biological Sciences. 272 (1572): 1557–1560. doi:10.1098/rspb.2005.3109. PMC 1559837. PMID 16048770.
  4. ^ a b "What is specific impulse?". Qualitative Reasoning Group. Retrieved 22 December 2009.
  5. ^ a b Benson, Tom (11 July 2008). "Specific impulse". NASA. Archived from the original on 24 January 2010. Retrieved 22 December 2009.
  6. ^ Hutchinson, Lee (14 April 2013). "New F-1B rocket engine upgrades Apollo-era design with 1.8M lbs of thrust". Ars Technica. Retrieved 15 April 2013. The measure of a rocket's fuel effectiveness is called its specific impulse (abbreviated as 'ISP'—or more properly Isp).... 'Mass specific impulse...describes the thrust-producing effectiveness of a chemical reaction and it is most easily thought of as the amount of thrust force produced by each pound (mass) of fuel and oxidizer propellant burned in a unit of time. It is kind of like a measure of miles per gallon (mpg) for rockets.'
  7. ^ Wake, M.H. (1993). "The Skull as a Locomotor Organ". In Hanken, James (ed.). The Skull. University of Chicago Press. p. 460. ISBN 978-0-226-31573-7.
  8. ^ Mill, P. J.; Pickard, R. S. (1975). "Jet-propulsion in anisopteran dragonfly larvae". Journal of Comparative Physiology. 97 (4): 329–338. doi:10.1007/BF00631969. S2CID 45066664.
  9. ^ Chamberlain Jr, John A. (1987). "32. Locomotion of Nautilus". In Saunders, W. B.; Landman, N. H. (eds.). Nautilus: The Biology and Paleobiology of a Living Fossil. ISBN 9789048132980.
  10. ^ Bone, Q.; Trueman, E. R. (2009). "Jet propulsion of the calycophoran siphonophores Chelophyes and Abylopsis". Journal of the Marine Biological Association of the United Kingdom. 62 (2): 263–276. doi:10.1017/S0025315400057271. S2CID 84754313.
  11. ^ a b Bone, Q.; Trueman, E. R. (2009). "Jet propulsion in salps (Tunicata: Thaliacea)". Journal of Zoology. 201 (4): 481–506. doi:10.1111/j.1469-7998.1983.tb05071.x.
  12. ^ Bone, Q.; Trueman, E. (1984). "Jet propulsion in Doliolum (Tunicata: Thaliacea)". Journal of Experimental Marine Biology and Ecology. 76 (2): 105–118. doi:10.1016/0022-0981(84)90059-5.
  13. ^ Demont, M. Edwin; Gosline, John M. (January 1, 1988). "Mechanics of Jet Propulsion in the Hydromedusan Jellyfish, Polyorchis Pexicillatus: I. Mechanical Properties of the Locomotor Structure". J. Exp. Biol. 134 (134): 313–332. doi:10.1242/jeb.134.1.313.
  14. ^ Demont, M. Edwin; Gosline, John M. (January 1, 1988). "Mechanics of Jet Propulsion in the Hydromedusan Jellyfish, Polyorchis Pexicillatus: II. Energetics of the Jet Cycle". J. Exp. Biol. 134 (134): 333–345. doi:10.1242/jeb.134.1.333.
  15. ^ Demont, M. Edwin; Gosline, John M. (January 1, 1988). "Mechanics of Jet Propulsion in the Hydromedusan Jellyfish, Polyorchis Pexicillatus: III. A Natural Resonating Bell; The Presence and Importance of a Resonant Phenomenon in the Locomotor Structure". J. Exp. Biol. 134 (134): 347–361. doi:10.1242/jeb.134.1.347.
  16. ^ Madin, L. P. (1990). "Aspects of jet propulsion in salps". Canadian Journal of Zoology. 68 (4): 765–777. doi:10.1139/z90-111.
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