Electrohydrodynamic thruster
Encyclopedia
An electrohydrodynamic thruster is a high voltage device that propels air or fluids to achieve relative motion. EHD thrusters, unlike ion thruster
Ion thruster
An ion thruster is a form of electric propulsion used for spacecraft propulsion that creates thrust by accelerating ions. Ion thrusters are categorized by how they accelerate the ions, using either electrostatic or electromagnetic force. Electrostatic ion thrusters use the Coulomb force and...
s, do not carry their own propellant and thus cannot operate in space or vacuum.
What is an EHD thruster
An EHD thruster is a propulsion device based on ionic fluid propulsion which works without moving parts, using only electrical energy. The principle of ionic (air) propulsion with corona-generated charged particles has been known since the earliest days of the discovery of electricity, with references dating back to year 1709 in a book titled Physico-Mechanical Experiments on Various Subjects by Francis HauksbeeFrancis Hauksbee
Francis Hauksbee the elder , also known as Francis Hawksbee, was an 18th-century English scientist, and a Fellow of the Royal Society...
. The first publicly demonstrated tethered model was developed by Major De Seversky in the form of an Ionocraft
Ionocraft
An ionocraft or ion-propelled aircraft, commonly known as a lifter or hexalifter, is an electrohydrodynamic device to produce thrust in the air, without requiring any combustion or moving parts. The term "Ionocraft" dates back to the 1960s, an era in which EHD experiments were at their peak...
, a single stage EHD thruster, in which the thruster lifts itself by propelling air downwards (see Newton's Third Law of Motion
Newton's laws of motion
Newton's laws of motion are three physical laws that form the basis for classical mechanics. They describe the relationship between the forces acting on a body and its motion due to those forces...
). De Seversky contributed much to its basic physics and its construction variations during the year 1960 and has in fact patented his device . Only electric fields are used in this propulsion method.
The basic components of an EHD thruster are two: an ioniser
Air ioniser
An air ioniser is a device that uses high voltage to ionise air molecules. Negative ions, or anions, are particles with one or more extra electrons, conferring a net negative charge to the particle. Cations are positive ions missing one or more electrons, resulting in a net positive charge...
and an ion accelerator. Ionocraft
Ionocraft
An ionocraft or ion-propelled aircraft, commonly known as a lifter or hexalifter, is an electrohydrodynamic device to produce thrust in the air, without requiring any combustion or moving parts. The term "Ionocraft" dates back to the 1960s, an era in which EHD experiments were at their peak...
s form part of this category, but their energy conversion efficiency is severely limited to less than 1% by the fact that the ioniser and accelerating mechanisms are not independent. Unlike the ionocraft
Ionocraft
An ionocraft or ion-propelled aircraft, commonly known as a lifter or hexalifter, is an electrohydrodynamic device to produce thrust in the air, without requiring any combustion or moving parts. The term "Ionocraft" dates back to the 1960s, an era in which EHD experiments were at their peak...
, within an EHD thruster, the air gap in its second stage is not restricted or related to the Corona discharge
Corona discharge
In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor that is electrically energized...
voltage of its ionising stage. Also, EHD thrusters are not restricted to air as their main propulsion fluid, and work perfectly in other fluids, such as oil.
EHD thruster operation
The first stage consists of a powerful air ioniserAir ioniser
An air ioniser is a device that uses high voltage to ionise air molecules. Negative ions, or anions, are particles with one or more extra electrons, conferring a net negative charge to the particle. Cations are positive ions missing one or more electrons, resulting in a net positive charge...
which, when supplied by high voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
in the kilovolt to megavolt range, ionises the intake air into ion clouds which flow into the second stage of the device.
The second stage consists of one or multiple stages of ion accelerators, powered by voltages in the kilovolt or megavolt range, in which the ionised fluid is moved on a straight path along the length of the accelerating unit. Movement of the ion clouds can be electronically controlled to increase the effective efficiency. Within this path, the ions travel at a constant drift velocity
Drift velocity
The drift velocity is the average velocity that a particle, such as an electron, attains due to an electric field. It can also be referred to as Axial Drift Velocity since particles defined are assumed to be moving along a plane. In general, an electron will 'rattle around' in a conductor at the...
and multiple impacts occur with the neutral fluid molecules present in the accelerating unit, which is open to the surrounding fluid. In accordance with Newton's Third Law of motion, the thruster will be acted upon by an equal and opposite force to the total force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...
exerted by the ions over the neutral fluid within the second stage.
Optionally, the temperature, pressure and fluid constituents may be synthesised within the accelerating stage to increase the efficiency of momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
transfer between the charged ions and the neutral fluid molecules. The charged ions are then neutralised on their exit from the second stage. The electrical to mechanical conversion efficiency is equal to the ratio of the velocity of the neutral fluid to that of the moving ions. In a single stage ionocraft
Ionocraft
An ionocraft or ion-propelled aircraft, commonly known as a lifter or hexalifter, is an electrohydrodynamic device to produce thrust in the air, without requiring any combustion or moving parts. The term "Ionocraft" dates back to the 1960s, an era in which EHD experiments were at their peak...
type EHD thruster, this ratio is typically equal to 1 m/s:100 m/s or 1%. A well engineered EHD thruster can achieve a much higher degree of electrical to mechanical conversion efficiency with the correct design parameters.. The remaining losses would be mainly due to the mechanical drag of the thruster physical structure.
See also
- Field Emission Electric PropulsionField Emission Electric PropulsionField-emission electric propulsion is an advanced electrostatic propulsion concept, a form of ion thruster, that uses liquid metal as a propellant. A FEEP device consists of an emitter and an accelerator electrode...
- Hall effect thrusterHall effect thrusterIn spacecraft propulsion, a Hall thruster is a type of ion thruster in which the propellant is accelerated by an electric field. Hall thrusters trap electrons in a magnetic field and then use the electrons to ionize propellant, efficiently accelerate the ions to produce thrust, and neutralize the...
- Ion windIon windIon wind, ionic wind, or coronal wind is a stream of ionized fluid generated by a strong electric field. Francis Hauksbee, curator of instruments for the Royal Society of London, made the earliest report of electric wind in 1709...
- Ion thrusterIon thrusterAn ion thruster is a form of electric propulsion used for spacecraft propulsion that creates thrust by accelerating ions. Ion thrusters are categorized by how they accelerate the ions, using either electrostatic or electromagnetic force. Electrostatic ion thrusters use the Coulomb force and...
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- Pulsed inductive thrusterPulsed inductive thrusterPulsed inductive thrusters are a form of ion thruster, used in spacecraft propulsion. A PIT uses perpendicular electric and magnetic fields to accelerate a propellant. A nozzle releases a puff of gas which spreads across a flat induction coil of wire about 1 meter across...
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