Pulse Jet Engine
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300px, Diagram of a pulsejet A pulsejet engine (or pulse jet) is a type of
jet engine A jet engine is a type of reaction engine discharging a fast-moving jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include rocket, Pump-jet, water jet, and hybrid propulsion, the term ...
in which combustion occurs in
pulse In medicine, a pulse represents the tactile arterial palpation of the cardiac cycle (heartbeat) by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the nec ...
s. A pulsejet engine can be made with few or no
moving parts Machines include both fixed and moving parts. The moving parts have controlled and constrained motions. Moving parts are machine components excluding any moving fluids, such as fuel, coolant or hydraulic fluid. Moving parts also do not include ...
, and is capable of running statically (i.e. it does not need to have air forced into its inlet, typically by forward motion). The best known example may be the
Argus As 109-014 The Argus As 014 (designated 109-014 by the Ministry of Aviation (Germany), RLM) was a pulsejet engine used on the German V-1 flying bomb of World War II, and the first model of pulsejet engine placed in mass production. License manufacture of t ...
used to propel
Nazi Germany Nazi Germany (lit. "National Socialist State"), ' (lit. "Nazi State") for short; also ' (lit. "National Socialist Germany") (officially known as the German Reich from 1933 until 1943, and the Greater German Reich from 1943 to 1945) was ...
's
V-1 flying bomb The V-1 flying bomb (german: Vergeltungswaffe 1 "Vengeance Weapon 1") was an early cruise missile. Its official Ministry of Aviation (Nazi Germany), Reich Aviation Ministry () designation was Fi 103. It was also known to the Allies as the buz ...
. Pulsejet engines are a lightweight form of jet propulsion, but usually have a poor
compression ratio The compression ratio is the ratio between the volume of the cylinder and combustion chamber in an internal combustion engine at their maximum and minimum values. A fundamental specification for such engines, it is measured two ways: the stati ...
, and hence give a low
specific impulse Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine (a rocket using propellant or a jet engine using fuel) creates thrust. For engines whose reaction mass is only the fuel they carry, specific impulse i ...
. There are two main types of pulsejet engines, both of which use resonant combustion and harness the expanding combustion products to form a pulsating exhaust jet that produces thrust intermittently. The first is known as a valved or traditional pulsejet and it has a set of one-way valves through which the incoming air passes. When the air-fuel is ignited, these valves slam shut, which means that the hot gases can only leave through the engine's tailpipe, thus creating forward thrust. The second type of pulsejet is known as the valveless pulsejet. Technically the term for this engine is the acoustic-type pulsejet, or aerodynamically valved pulsejet. One notable line of research of pulsejet engines includes the pulse detonation engine, which involves repeated detonations in the engine, and which can potentially give high compression and reasonably good efficiency.


History

left, Ramón Casanova and the pulsejet engine he constructed and patented in 1917 Russian inventor and retired artillery officer Nikolaj Afanasievich Teleshov patented a steam pulsejet engine in 1867 while Swedish inventor
Martin Wiberg Martin Wiberg (September 4, 1826 – December 29, 1905) was a Swedish inventor. He enrolled at Lund University in 1845 and became a Doctor of Philosophy in 1850. He is known as a computer pioneer for his c. 1859 (1857-1860) invention of a machi ...
also has a claim to having invented the first pulsejet, in Sweden, but details are unclear. The first working pulsejet was patented in 1906 by Russian engineer V.V. Karavodin, who completed a working model in 1907. The French inventor Georges Marconnet patented his valveless pulsejet engine in 1908, and Ramón Casanova, in
Ripoll Ripoll () is the capital of the ''comarca'' of Ripollès, in the province of Girona, Catalonia, Spain. It is located on confluence of the Ter River and its tributary Freser, next to the Pyrenees near the French border. The population was 11, ...
,
Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , i ...
patented a pulsejet in
Barcelona Barcelona ( , , ) is a city on the coast of northeastern Spain. It is the capital and largest city of the autonomous community of Catalonia, as well as the second most populous municipality of Spain. With a population of 1.6 million within ci ...
in 1917, having constructed one beginning in 1913.
Robert Goddard Robert Hutchings Goddard (October 5, 1882 – August 10, 1945) was an American engineer, professor, physicist, and inventor who is credited with creating and building the world's first liquid-fueled rocket. Goddard successfully laun ...
invented a pulsejet engine in 1931, and demonstrated it on a jet-propelled bicycle. Engineer Paul Schmidt pioneered a more efficient design based on modification of the intake valves (or flaps), earning him government support from the German Air Ministry in 1933.George Mindling, Robert Bolton: ''US Airforce Tactical Missiles:1949–1969: The Pioneers'', Lulu.com, 200: . pp6-31 In 1909, Georges Marconnet developed the first pulsating combustor without valves. It was the grandfather of all valveless pulsejets. The valveless pulsejet was experimented with by the French propulsion research group
SNECMA Safran Aircraft Engines, previously Snecma (''Société nationale d'études et de construction de moteurs d'aviation'') or Snecma Moteurs, is a French aerospace engine manufacturer headquartered in Courcouronnes and a subsidiary of Safran. It ...
(Société Nationale d'Étude et de Construction de Moteurs d'Aviation ), in the late 1940s. The valveless pulsejet's first widespread use was the Dutch drone
Aviolanda AT-21 The Aviolanda AT-21 was a target drone developed in the Netherlands by Aviolanda. Powered by a pulsejet engine, it was the Netherlands' first drone to be successfully developed, and saw limited use in the late 1950s and early 1960s. Design and ...


Argus As 109-014

In 1934,
Georg Hans Madelung Georg Hans Madelung (31 July 1889 in Rostock – 17 August 1972 in Uffing) was a Germans, German academic and aeronautical engineer. Madelung studied at several German Technical University, Technical Universities before his service as a pilot ...
and Munich-based Paul Schmidt proposed to the German
Air Ministry The Air Ministry was a department of the Government of the United Kingdom with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964. It was under the political authority of the Secretary of State ...
a "flying bomb" powered by Schmidt's pulsejet. Madelung co-invented the
ribbon parachute A parachute is a device used to slow the motion of an object through an atmosphere by creating drag or, in a ram-air parachute, aerodynamic lift. A major application is to support people, for recreation or as a safety device for aviators, who ...
, a device used to stabilise the
V-1 V1, V01 or V-1 can refer to version one (for anything) (e.g., see version control) V1, V01 or V-1 may also refer to: In aircraft * V-1 flying bomb, a World War II German weapon * V1 speed, the maximum speed at which an aircraft pilot may abort ...
in its terminal dive. Schmidt's prototype bomb failed to meet German Air Ministry specifications, especially owing to poor accuracy, range and high cost. The original Schmidt design had the pulsejet placed in a fuselage like a modern jet fighter, unlike the eventual V-1, which had the engine placed above the warhead and fuselage. The Argus Company began work based on Schmidt's work. Other German manufacturers working on similar pulsejets and flying bombs were
The Askania Company ''The'' () is a grammatical article in English, denoting persons or things already mentioned, under discussion, implied or otherwise presumed familiar to listeners, readers, or speakers. It is the definite article in English. ''The'' is the ...
,
Robert Lusser Robert Lusser (19 April 1899 – 19 January 1969) was a German engineer, aircraft designer and aviator. He is remembered both for several well-known Messerschmitt and Heinkel designs during World War II, and after the war for his theoretical study o ...
of
Fieseler The Gerhard Fieseler Werke (GFW) in Kassel was a German aircraft manufacturer of the 1930s and 1940s. The company is remembered mostly for its military aircraft built for the Luftwaffe during the Second World War. History The firm was founded o ...
, Dr. Fritz Gosslau of Argus and the
Siemens Siemens AG ( ) is a German multinational conglomerate corporation and the largest industrial manufacturing company in Europe headquartered in Munich with branch offices abroad. The principal divisions of the corporation are ''Industry'', '' ...
company, which were all combined to work on the V-1. With Schmidt now working for Argus, the pulsejet was perfected and was officially known by its RLM designation as the Argus As 109-014. The first unpowered drop occurred at
Peenemünde Peenemünde (, en, "Peene iverMouth") is a municipality on the Baltic Sea island of Usedom in the Vorpommern-Greifswald district in Mecklenburg-Vorpommern, Germany. It is part of the ''Amt'' (collective municipality) of Usedom-Nord. The communi ...
on 28 October 1942 and the first powered flight on 10 December 1942. The pulsejet was evaluated to be an excellent balance of cost and function: a simple design that performed well for minimal cost. It would run on any grade of petroleum and the ignition shutter system was not intended to last beyond the V-1's normal operational flight life of one hour. Although it generated insufficient thrust for takeoff, the V-1's resonant jet could operate while stationary on the launch ramp. The simple resonant design based on the ratio (8.7:1) of the diameter to the length of the exhaust pipe functioned to perpetuate the combustion cycle, and attained stable resonance frequency at 43
cycles per second The cycle per second is a once-common English name for the unit of frequency now known as the hertz (Hz). The plural form was typically used, often written cycles per second, cycles/second, c.p.s., c/s, or, ambiguously, just cycles (Cy./Cyc.). T ...
. The engine produced of static thrust and approximately in flight. Ignition in the As 014 was provided by a single automotive spark plug, mounted approximately behind the front-mounted valve array. The spark only operated for the start sequence for the engine; the Argus As 014, like all pulsejets, did not require
ignition coil An ignition coil (also called a spark coil) is an induction coil in an automobile's ignition system that transforms the battery's voltage to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel. So ...
s or
magnetos A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current. It is categorized as a form of alternator, ...
for ignition â€” the ignition source being the tail of the preceding fireball during the run. The engine casing did not provide sufficient heat to cause diesel-type ignition of the fuel, as there is insignificant compression within a pulsejet engine. The Argus As 014 valve array was based on a shutter system that operated at the 43 to 45 cycles-per-second frequency of the engine. Three air nozzles in the front of the Argus As 014 were connected to an external high pressure source to start the engine. The fuel used for ignition was
acetylene Acetylene (systematic name: ethyne) is the chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure ...
, with the technicians having to place a baffle of wood or cardboard in the exhaust pipe to stop the acetylene diffusing before complete ignition. Once the engine ignited and minimum
operating temperature An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
was attained, external hoses and connectors were removed. The V-1, being a cruise missile, lacked landing gear, instead the Argus As 014 was launched on an inclined ramp powered by a
piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tig ...
-driven steam catapult. Steam power to fire the piston was generated by the violent
exothermic In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e ...
chemical reaction created when
hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%†...
and
potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, that dissolves in water as K+ and , an intensely pink to purple solution. Potassium permanganate is widely used in the c ...
(termed
T-Stoff T-Stoff (; 'substance T') was a stabilised high test peroxide used in Germany during World War II. T-Stoff was specified to contain 80% (occasionally 85%) hydrogen peroxide (H2O2), remainder water, with traces (<0.1%) of stabilisers. Stabilisers ...
and
Z-Stoff Z-Stoff (, "substance Z") was a name for calcium permanganate or sodium permanganate mixed in water. It was normally used as a catalyst for T-Stoff ( high-test peroxide) in military rocket programs by Nazi Germany during World War II. Z-Stoff was ...
) are combined. The principal military use of the pulsejet engine, with the volume production of the Argus As 014 unit (the first pulsejet engine ever in volume production), was for use with the
V-1 flying bomb The V-1 flying bomb (german: Vergeltungswaffe 1 "Vengeance Weapon 1") was an early cruise missile. Its official Ministry of Aviation (Nazi Germany), Reich Aviation Ministry () designation was Fi 103. It was also known to the Allies as the buz ...
. The engine's characteristic droning noise earned it the nicknames "buzz bomb" or "doodlebug". The V-1 was a German
cruise missile A cruise missile is a guided missile used against terrestrial or naval targets that remains in the atmosphere and flies the major portion of its flight path at approximately constant speed. Cruise missiles are designed to deliver a large warhe ...
used in
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, most famously in the bombing of London in 1944. Pulsejet engines, being cheap and easy to construct, were the obvious choice for the V-1's designers, given the Germans' materials shortages and overstretched industry at that stage of the war. Designers of modern cruise missiles do not choose pulsejet engines for propulsion, preferring
turbojet The turbojet is an airbreathing jet engine which is typically used in aircraft. It consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet which includes inlet guide vanes, a compressor, a combustion chamber, and ...
s or
rocket A rocket (from it, rocchetto, , bobbin/spool) is a vehicle that uses jet propulsion to accelerate without using the surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Rocket engines work entirely fr ...
engines. The only other uses of the pulsejet that reached the hardware stage in Nazi Germany were the
Messerschmitt Me 328 The Messerschmitt Me 328 was originally designed as a parasite aircraft to protect '' Luftwaffe'' bomber formations during World War II. During its protracted development, a wide variety of other roles were suggested for it. Late in the war, th ...
and an experimental Einpersonenfluggerät project for the German Heer.
Wright Field Wilbur Wright Field was a military installation and an airfield used as a World War I pilot, mechanic, and armorer training facility and, under different designations, conducted United States Army Air Corps and Air Forces flight testing. Loca ...
technical personnel
reverse-engineered Reverse engineering (also known as backwards engineering or back engineering) is a process or method through which one attempts to understand through deductive reasoning how a previously made device, process, system, or piece of software accompli ...
the V-1 from the remains of one that had failed to detonate in Britain. The result was the creation of the JB-2 Loon, with the airframe built by
Republic Aviation The Republic Aviation Corporation was an American aircraft manufacturer based in Farmingdale, New York, on Long Island, New York, Long Island. Originally known as the Seversky Aircraft Company, the company was responsible for the design and produc ...
, and the Argus As 014 reproduction pulsejet powerplant, known by its PJ31 American designation, being made by the
Ford Motor Company Ford Motor Company (commonly known as Ford) is an American multinational automobile manufacturer headquartered in Dearborn, Michigan, United States. It was founded by Henry Ford and incorporated on June 16, 1903. The company sells automobi ...
. General
Hap Arnold Henry Harley Arnold (June 25, 1886 â€“ January 15, 1950) was an American general officer holding the ranks of General of the Army and later, General of the Air Force. Arnold was an aviation pioneer, Chief of the Air Corps (1938–1941), ...
of the United States Army Air Forces was concerned that this weapon could be built of steel and wood, in 2000 man hours and approximate cost of US$600 (in 1943).


Design

Pulsejet engines are characterized by simplicity, low cost of construction, and high noise levels. While the
thrust-to-weight ratio Thrust-to-weight ratio is a dimensionless ratio of thrust to weight of a rocket, jet engine, propeller engine, or a vehicle propelled by such an engine that is an indicator of the performance of the engine or vehicle. The instantaneous thrust-to-w ...
is excellent,
thrust specific fuel consumption Thrust-specific fuel consumption (TSFC) is the fuel efficiency of an engine design with respect to thrust output. TSFC may also be thought of as fuel consumption (grams/second) per unit of thrust (newtons, or N), hence ''thrust-specific''. This fig ...
is very poor. The pulsejet uses the
Lenoir cycle The Lenoir cycle is an idealized thermodynamic cycle often used to model a pulse jet engine. It is based on the operation of an engine patented by Jean Joseph Etienne Lenoir in 1860. This engine is often thought of as the first commercially pr ...
, which, lacking an external compressive driver such as the
Otto cycle An Otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical spark ignition piston engine. It is the thermodynamic cycle most commonly found in automobile engines. The Otto cycle is a description of what happ ...
's piston, or the
Brayton cycle The Brayton cycle is a thermodynamic cycle that describes the operation of certain heat engines that have air or some other gas as their working fluid. The original Brayton engines used a piston compressor and piston expander, but modern gas tur ...
's compression turbine, drives compression with
acoustic resonance Acoustic resonance is a phenomenon in which an acoustic system amplifies sound waves whose frequency matches one of its own natural frequencies of vibration (its ''resonance frequencies''). The term "acoustic resonance" is sometimes used to nar ...
in a tube. This limits the maximum pre-combustion pressure ratio, to around 1.2 to 1. The high noise levels usually make them impractical for other than military and other similarly restricted applications.Jan Roskam, Chuan-Tau Edward Lan; ''Airplane aerodynamics and performance'', DARcorporation: 1997, , 711 pages However, pulsejets are used on a large scale as industrial drying systems, and there has been a resurgence in studying these engines for applications such as high-output heating, biomass conversion, and alternative energy systems, as pulsejets can run on almost anything that burns, including particulate fuels such as sawdust or coal powder. Pulsejets have been used to power experimental helicopters, the engines being attached to the ends of the rotor blades. In providing power to helicopter rotors, pulsejets have the advantage over turbine or piston engines of not producing
torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
upon the
fuselage The fuselage (; from the French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds crew, passengers, or cargo. In single-engine aircraft, it will usually contain an engine as well, although in some amphibious aircraft t ...
since they don't apply force to the shaft, but push the tips. A helicopter may then be built without a tail rotor and its associated transmission and drive shaft, simplifying the aircraft (
cyclic Cycle, cycles, or cyclic may refer to: Anthropology and social sciences * Cyclic history, a theory of history * Cyclical theory, a theory of American political history associated with Arthur Schlesinger, Sr. * Social cycle, various cycles in s ...
and
collective A collective is a group of entities that share or are motivated by at least one common issue or interest, or work together to achieve a common objective. Collectives can differ from cooperatives in that they are not necessarily focused upon an ...
control of the main rotor is still necessary). This concept was being considered as early as 1947 when the American Helicopter Company started work on its XA-5 Top Sergeant helicopter prototype powered by pulsejet engines at the rotor tips. The XA-5 first flew in January 1949 and was followed by the XA-6 Buck Private with the same pulsejet design. Also in 1949
Hiller Helicopters Hiller Aircraft Company was founded in 1942 as Hiller Industries by Stanley Hiller to develop helicopters. History Stanley Hiller, then seventeen, established the first helicopter factory on the West Coast of the United States, located in Berkele ...
built and tested the Hiller Powerblade, the world's first hot-cycle pressure-jet rotor. Hiller switched to tip mounted ramjets but American Helicopter went on to develop the XA-8 under a U.S. Army contract. It first flew in 1952 and was known as the
XH-26 Jet Jeep The American Helicopter XH-26 Jet Jeep (known as the XA-8 by its manufacturer) was an experimental tip jet helicopter developed in 1951 by the American Helicopter Company to meet a United States Army and Air Force (USAF) request for a collapsibl ...
. It used XPJ49 pulsejets mounted at the rotor tips. The XH-26 met all its main design objectives but the Army cancelled the project because of the unacceptable level of noise of the pulsejets and the fact that the drag of the pulsejets at the rotor tips made
autorotation Autorotation is a state of flight in which the main rotor system of a helicopter or other rotary-wing aircraft turns by the action of air moving up through the rotor, as with an autogyro, rather than engine power driving the rotor. Bensen, Igor ...
landings very problematic. Rotor-tip propulsion has been claimed to reduce the cost of production of rotary-wing craft to 1/10 of that for conventional powered rotary-wing aircraft. Pulsejets have also been used in both control-line and radio-controlled model aircraft. The speed record for control-line pulsejet-powered model aircraft is greater than 200 miles per hour (323 km/h). The speed of a free-flying radio-controlled pulsejet is limited by the engine's intake design. At around 450 km/h (280 mph) most valved engines' valve systems stop fully closing owing to ram air pressure, which results in performance loss. Variable intake geometry lets the engine produce full power at most speeds by optimizing for whatever speed at which the air enters the pulsejet. Valveless designs are not as negatively affected by ram air pressure as other designs, as they were never intended to stop the flow out of the intake, and can significantly increase in power at speed. Another feature of pulsejet engines is that their thrust can be increased by a specially shaped duct placed behind the engine. The duct acts as an
annular wing A closed wing is a wing that effectively has two main planes which merge at their ends so that there are no conventional wing tips. Closed wing designs include the annular wing (commonly known as the cylindrical or ring wing), the joined wing, ...
, which evens out the pulsating thrust, by harnessing aerodynamic forces in the pulsejet exhaust. The duct, typically called an augmentor, can significantly increase the thrust of a pulsejet with no additional fuel consumption. Gains of 100% increases in thrust are possible, resulting in a much higher fuel efficiency. However, the larger the augmenter duct, the more drag it produces, and it is only effective within specific speed ranges.


Operation


Valved designs

Valved pulsejet engines use a mechanical valve to control the flow of expanding exhaust, forcing the hot gas to go out of the back of the engine through the tailpipe only, and allow fresh air and more fuel to enter through the
intake An intake (also inlet) is an opening, structure or system through which a fluid is admitted to a space or machine as a consequence of a pressure differential between the outside and the inside. The pressure difference may be generated on the ins ...
as the inertia of the escaping exhaust creates a partial vacuum for a fraction of a second after each detonation. This draws in additional air and fuel between pulses. The valved pulsejet comprises an intake with a one-way valve arrangement. The valves prevent the explosive gas of the ignited fuel mixture in the
combustion chamber A combustion chamber is part of an internal combustion engine in which the fuel/air mix is burned. For steam engines, the term has also been used for an extension of the firebox which is used to allow a more complete combustion process. Interna ...
from exiting and disrupting the intake airflow, although with all practical valved pulsejets there is some 'blowback' while running statically or at low speed, as the valves cannot close fast enough to prevent some gas from exiting through the intake. The superheated exhaust gases exit through an acoustically
resonant Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscilla ...
exhaust pipe. The intake valve is typically a
reed valve Reed valves are a type of check valve which restrict the flow of fluids to a single direction, opening and closing under changing pressure on each face. Modern versions often consist of flexible metal or composite materials (fiberglass or carbon f ...
. The two most common configurations are the daisy valve, and the rectangular valve grid. A daisy valve consists of a thin sheet of material to act as the reed, cut into the shape of a stylized daisy with "petals" that widen towards their ends. Each "petal" covers a circular intake hole at its tip. The daisy valve is bolted to the manifold through its centre. Although easier to construct on a small scale, it is less effective than a valve grid. The cycle frequency is primarily dependent on the length of the engine. For a small model-type engine the frequency may be around 250 pulses per second, whereas for a larger engine such as the one used on the German
V-1 flying bomb The V-1 flying bomb (german: Vergeltungswaffe 1 "Vengeance Weapon 1") was an early cruise missile. Its official Ministry of Aviation (Nazi Germany), Reich Aviation Ministry () designation was Fi 103. It was also known to the Allies as the buz ...
, the frequency was closer to 45 pulses per second. The low-frequency sound produced resulted in the missiles being nicknamed "buzz bombs."


Valveless designs

Valveless pulsejet engines have no moving parts and use only their geometry to control the flow of exhaust out of the engine. Valveless pulsejets expel exhaust out of both the
intake An intake (also inlet) is an opening, structure or system through which a fluid is admitted to a space or machine as a consequence of a pressure differential between the outside and the inside. The pressure difference may be generated on the ins ...
s and the exhaust, but the majority of the force produced leaves through the wider cross section of the exhaust. The larger amount of mass leaving the wider exhaust has more inertia than the backwards flow out of the intake, allowing it to produce a partial vacuum for a fraction of a second after each detonation, reversing the flow of the intake to its proper direction, and therefore ingesting more air and fuel. This happens dozens of times per second. The valveless pulsejet operates on the same principle as the valved pulsejet, but the 'valve' is the engine's geometry. Fuel, as a gas or atomized liquid spray, is either mixed with the air in the intake or directly injected into the
combustion chamber A combustion chamber is part of an internal combustion engine in which the fuel/air mix is burned. For steam engines, the term has also been used for an extension of the firebox which is used to allow a more complete combustion process. Interna ...
. Starting the engine usually requires forced air and an ignition source, such as a spark plug, for the fuel-air mix. With modern manufactured engine designs, almost any design can be made to be self-starting by providing the engine with fuel and an ignition spark, starting the engine with no compressed air. Once running, the engine only requires input of fuel to maintain a self-sustaining combustion cycle. The combustion cycle comprises five or six phases depending on the engine: Induction, Compression, (optional) Fuel Injection, Ignition, Combustion, and Exhaust. Starting with ignition within the combustion chamber, a high pressure is raised by the combustion of the fuel-air mixture. The pressurized gas from combustion cannot exit forward through the one-way intake valve and so exits only to the rear through the exhaust tube. The inertial reaction of this gas flow causes the engine to provide thrust, this force being used to propel an airframe or a rotor blade. The inertia of the traveling exhaust gas causes a low pressure in the combustion chamber. This pressure is less than the inlet pressure (upstream of the one-way valve), and so the induction phase of the cycle begins. In the simplest of pulsejet engines this intake is through a venturi, which causes fuel to be drawn from a fuel supply. In more complex engines the fuel may be injected directly into the combustion chamber. When the induction phase is under way, fuel in atomized form is injected into the combustion chamber to fill the vacuum formed by the departing of the previous fireball; the atomized fuel tries to fill up the entire tube including the tailpipe. This causes atomized fuel at the rear of the combustion chamber to "flash" as it comes in contact with the hot gases of the preceding column of gas—this resulting flash "slams" the reed-valves shut or in the case of valveless designs, stops the flow of fuel until a vacuum is formed and the cycle repeats. Valveless pulsejets come in a number of shapes and sizes, with different designs being suited for different functions. A typical valveless engine will have one or more intake tubes, a combustion chamber section, and one or more exhaust tube sections. The intake tube takes in air and mixes it with fuel to combust, and also controls the expulsion of exhaust gas, like a valve, limiting the flow but not stopping it altogether. While the fuel-air mixture burns, most of the expanding gas is forced out of the exhaust pipe of the engine. Because the intake tube(s) also expel gas during the exhaust cycle of the engine, most valveless engines have the intakes facing backwards so that the thrust created adds to the overall thrust, rather than reducing it. The combustion creates two pressure wave fronts, one traveling down the longer exhaust tube and one down the short intake tube. By properly 'tuning' the system (by designing the engine dimensions properly), a resonating combustion process can be achieved. While some valveless engines are known for being extremely fuel-hungry, other designs use significantly less fuel than a valved pulsejet, and a properly designed system with advanced components and techniques can rival or exceed the fuel efficiency of small turbojet engines. A properly designed valveless engine will excel in flight as it does not have valves, and ram air pressure from traveling at high speed does not cause the engine to stop running like a valved engine. They can achieve higher top speeds, with some advanced designs being capable of operating at Mach .7 or possibly higher. The advantage of the acoustic-type pulsejet is simplicity. Since there are no
moving parts Machines include both fixed and moving parts. The moving parts have controlled and constrained motions. Moving parts are machine components excluding any moving fluids, such as fuel, coolant or hydraulic fluid. Moving parts also do not include ...
to wear out, they are easier to maintain and simpler to construct.


Future uses

Pulsejets are used today in
target drone A target drone is an unmanned aerial vehicle, generally remote controlled, usually used in the training of anti-aircraft crews. One of the earliest drones was the British DH.82 Queen Bee, a variant of the Tiger Moth trainer aircraft operationa ...
aircraft, flying
control line Control line (also called U-Control) is a simple and light way of controlling a flying model aircraft. The aircraft is connected to the operator by a pair of lines, attached to a handle, that work the elevator An elevator or lift is ...
model aircraft A model aircraft is a small unmanned aircraft. Many are replicas of real aircraft. Model aircraft are divided into two basic groups: flying and non-flying. Non-flying models are also termed static, display, or shelf models. Aircraft manufactur ...
(as well as radio-controlled aircraft), fog generators, and industrial drying and home heating equipment. Because pulsejets are an efficient and simple way to convert fuel into heat, experimenters are using them for new industrial applications such as biomass fuel conversion, and boiler and heater systems. Some experimenters continue to work on improved designs. The engines are difficult to integrate into commercial manned aircraft designs because of noise and vibration, though they excel on the smaller-scale unmanned vehicles. The pulse detonation engine (PDE) marks a new approach towards non-continuous jet engines and promises higher fuel efficiency compared to
turbofan The turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft engine, aircraft propulsion. The word "turbofan" is a portmanteau of "turbine" and "fan": the ''turbo'' portion refers to a gas turbine engine which ac ...
jet engines, at least at very high speeds.
Pratt & Whitney Pratt & Whitney is an American aerospace manufacturer with global service operations. It is a subsidiary of Raytheon Technologies. Pratt & Whitney's aircraft engines are widely used in both civil aviation (especially airlines) and military aviat ...
and
General Electric General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable energ ...
now have active PDE research programs. Most PDE research programs use pulsejet engines for testing ideas early in the design phase.
Boeing The Boeing Company () is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, telecommunications equipment, and missiles worldwide. The company also provides leasing and product ...
has a proprietary pulsejet engine technology called
Pulse Ejector Thrust Augmentor A Pulse Ejector Thrust Augmentor or PETA is a proprietary pulse jet engine developed by Boeing. The Boeing PETA design embeds the pulse jet inside a thrust augmenting duct which entrains surrounding air into the exhaust stream. This entrained air i ...
(PETA), which proposes to use pulsejet engines for vertical lift in military and commercial
VTOL A vertical take-off and landing (VTOL) aircraft is one that can take off and land vertically without relying on a runway. This classification can include a variety of types of aircraft including helicopters as well as thrust-vectoring fixed-win ...
aircraft.


See also

*
List of aircraft engines This is an alphabetical list of aircraft engines by manufacturer. 0–9 2si *2si 215 *2si 230 * 2si 430 * 2si 460 *2si 500 * 2si 540 * 2si 690 3W ''Source: RMV'' *3W 106iB2 *3W-110 *3W-112 *3W-170 *3W-210 *3W-220 A Abadal (Fr ...
*
Gluhareff Pressure Jet The Gluhareff Pressure Jet (or tip jet) is a type of jet engine that, like a valveless pulse jet, has no moving parts. It was invented by Eugene Michael Gluhareff, a Russian-American engineer who envisioned it as a power plant for personal hel ...


References


Further reading

* ''Aeronautical Engineering Review'', Institute of the Aeronautical Sciences (U.S.): 1948, vol. 7. * George Mindling, Robert Bolton: ''US Airforce Tactical Missiles:1949–1969: The Pioneers'', Lulu.com, 200: . pp6–31


External links


pulse-jets.com: An international site dedicated to pulsejets, including design and experimentation. Includes an extremely active forum composed of knowledgeable enthusiasts

Video of 21st century-built German reproduction Argus As 014 pulsejet testing

Pulsejets in aeromodels

Popular Rotocraft Association
{{Webarchive, url=https://web.archive.org/web/20110207173218/http://pra.org/ , date=7 February 2011
Pulsejet Bike


* ttps://gizmodo.com/5824430 PETA (Pulse-Ejector-Thrust-Augmentors) article * ttps://www.youtube.com/watch?v=0VKL9o2bn28 Ramon Casanova's pulsejet
American Helicopter XA-5 Flight
Pulsejet 300px, Diagram of a pulsejet A pulsejet engine (or pulse jet) is a type of jet engine in which combustion occurs in pulses. A pulsejet engine can be made with few or no moving parts, and is capable of running statically (i.e. it does not need ...