Swing-piston engine
Encyclopedia
A swing-piston engine is a type of internal combustion engine
in which the pistons move in a circular motion inside a ring-shaped "cylinder", moving closer and further from each other to provide compression and expansion. Generally two sets of pistons are used, geared to move in a fixed relationship as they rotate around the cylinder. In some versions the pistons oscillate around a fixed center, as opposed to rotating around the entire engine. The design has also been referred to as a oscillating piston engine, vibratory engine when the pistons oscillate instead of rotate, or toroidal engine based on the shape of the "cylinder".
The basic concept is very similar to the Wankel engine
, the "traditional" rotary, but predates it by some time. It also shares a strong lineage with the free-piston engine
. Like those designs, the swing-piston cylinder has to be open on one side to connect to the crankshaft, and is thus subject to the same sorts of sealing problems as other rotary designs. In addition, the swing-piston design retains a reciprocating motion and all the disadvantages that entails, namely the need for vibration damping and balancing. If the design oscillates around a fixed point, it also requires some sort of crank system to convert the motion into a rotary one. For these reasons, it has been said that the swing-piston design combines all the disadvantages of the rotary with all the disadvantages of the reciprocating.
designs, prior to the widespread introduction of the steam turbine
. In these examples the "piston" is typically not cylindrical as in a modern internal combustion design, and is generally rectangular in cross-section as seen from the top, rotating in a flat disk "cylinder". From the side they are either flat plates or pie-wedge shaped. The term "swing-piston" is not entirely accurate in these cases, but the operating cycle is identical and is properly considered here.
The first known example was introduced by Elijah Galloway in 1829 for ship propulsion. It featured a single vane rotating through 270 degrees. It appears this version was never built, although a model still exists in the Science Museum
. Galloway also designed a wide variety of pure rotary engines using vanes as well.
A more serious attempt was the "Cambrian System" of John Jones in 1941. This design used two or three flat plates that were geared to move closer or further apart as the cycled continued. When the plates were at their closest point, steam was admitted between them using a valve, pushing them apart as the cycle continued. When the plates reached their maximum distance, an internal passage was uncovered that allowed the partially-expanded steam to flow across the center of the device into the area on the other side of the vanes, which were now at their minimum distance. In this fashion the design was effectively a compound engine.
Many variations followed, and a number of these would see limited use in the field. Notable among them was John Ericsson
's design of 1843, which powered the USS Princeton
, the United States
' first screw-powered steamship. Charles Parsons
also examined the concept and appears to have produced two swing-piston engine designs before moving on to the steam turbine
. The Roots brothers also designed a swing-piston engine of a unique type, although they are better known for their supercharger design.
World War II
-era design by Otto Lutz. His design had six pistons in total, three each attached to two disks. The disks were geared to each other to form six chambers between the pistons, such that at any one time one set of three chambers were "close together" while the other set of three was "wide apart", varying between those two extremes as the disks rotated. The timing was arranged such that the chambers reached their "close together" point over the spark plug, and their "wide apart" point over the intake and exhaust ports. This action is similar to the Wankel, the primary difference being that Wankel creates compression and expansion via the shaping of the engine and rotor, as opposed to the relative motion of the pistons.
Lutz's engine was being designed as an experimental gas generator
for a new type of aircraft engine
, one that replaced a traditional centrifugal
or axial compressor
with his swing-piston design. Ultimately the exhaust would be used to drive a turbine, that power being used to drive a propeller
to produce a turboprop
. For this role the exhaust gas was too hot to be used directly in a turbine, given the available materials, so the engine featured a second "exhaust port" that vented cold pressurized air, which was then mixed into the hot exhaust. For direct power use, as opposed to driving a turbine, this "third area" of the engine can simply be left open to the air to avoid losing power to compression that will not be used.
The initial test engines had some minor problems, notably with sealing, but these were worked through and the engines were under test during 1944. One particularly nice feature of swing-piston engines is that they can be bolted back to back along a common crank shaft to make a larger engine, and with each additional stage the running becomes smoother and the only part that needs to be made larger is the crankshaft. A similar arrangement with a radial engine
is generally more difficult to arrange, especially cooling, and ones with inline engine
arrangements soon become so long that keeping the crankshaft from vibrating becomes a serious problem (see Chrysler IV-2220 for example).
Each "cylinder" from Lutz's design was 0.70 m in diameter and only about 30 cm in depth, providing 445 hp from 140 kg, an excellent power-to-weight ratio
compared even to jet engines of the era. A five-block version was proposed for his turboprop concept, providing 3,450 hp from an engine about 2 m long. While the power-to-weight was good, the density of the engine was simply superb.
The overall turboprop looked much more like a jet engine than a piston one. The swing-piston gas generator was located in the middle of a long nacelle, with a five-stage axial compressor in front and a three-stage turbine behind. The compressor was used both to act as a supercharger
for the piston engine, as well as provide cold air to cool the turbine. The actual power to the propeller, combining both the pistons and the turbines, was 4,930 hp at 10,000 m altitude, far greater than any German wartime project.
Why all this complexity to produce a new version of an engine, the turboprop, whose primary advantage was simplicity? The main problem with conventional jet engines is that the combustion takes place in an open chamber, which is considerably less efficient than the closed chamber of a piston engine, where it has constant volume (or close to it). The Otto cycle
or Diesel cycle
used in piston engines has a much lower specific fuel consumption than the Brayton cycle
of a traditional gas turbine engines at low speed. Lutz's design was intended to power very long-range bomber
s and patrol aircraft, where fuel economy was more important than simplicity and outright performance.
Lutz later patented the design under "Rotary compressor and other engines", United States Patent 2,301,667.
experimented with a traditional engine with poppet valve
s on the combustion chambers, which had been used a number of times previously in experiments. Another approach entirely is to recover some of the heat of the exhaust in a heat exchanger
and use that instead of fuel to heat the compressed air, a concept used by General Motors
in a series of automobile turbines. Generally, however, improvements in the basic piston engine in "low power" roles have kept any of these advanced designs out of the marketplace.
More recently, starting in the 1990s, a number of inventors have re-introduced the concept as if it were new. Examples include Angel Labs' "Massive Yet Tiny" engine, the Rotoblock, the Roundengine, the Trochilic Engine and designs by Tschudi and Hoose.
In 2009 Russian billionaire industrialist Mikhail Prokhorov
announced his plans to enter an automotive business with a series of a lightweight hybrid vehicle
s utilizing this design as their prime mover
. Another recent introduction aimed at the hybrid market is the "Hüttlin Kugelmotor", which combines the swing-piston concept with a modified swashplate
to produce a spherical design that directly powers an internal electrical generator
.
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
in which the pistons move in a circular motion inside a ring-shaped "cylinder", moving closer and further from each other to provide compression and expansion. Generally two sets of pistons are used, geared to move in a fixed relationship as they rotate around the cylinder. In some versions the pistons oscillate around a fixed center, as opposed to rotating around the entire engine. The design has also been referred to as a oscillating piston engine, vibratory engine when the pistons oscillate instead of rotate, or toroidal engine based on the shape of the "cylinder".
The basic concept is very similar to the Wankel engine
Wankel engine
The Wankel engine is a type of internal combustion engine using an eccentric rotary design to convert pressure into a rotating motion instead of using reciprocating pistons. Its four-stroke cycle takes place in a space between the inside of an oval-like epitrochoid-shaped housing and a rotor that...
, the "traditional" rotary, but predates it by some time. It also shares a strong lineage with the free-piston engine
Free-piston engine
A free-piston engine is a linear, 'crankless' internal combustion engine, in which the piston motion is not controlled by a crankshaft but determined by the interaction of forces from the combustion chamber gases, a rebound device and a load device A free-piston engine is a linear, 'crankless'...
. Like those designs, the swing-piston cylinder has to be open on one side to connect to the crankshaft, and is thus subject to the same sorts of sealing problems as other rotary designs. In addition, the swing-piston design retains a reciprocating motion and all the disadvantages that entails, namely the need for vibration damping and balancing. If the design oscillates around a fixed point, it also requires some sort of crank system to convert the motion into a rotary one. For these reasons, it has been said that the swing-piston design combines all the disadvantages of the rotary with all the disadvantages of the reciprocating.
Steam engines
Swing-piston engines were initially introduced during the 1820s as alternate steam engineSteam engine
A steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be...
designs, prior to the widespread introduction of the steam turbine
Steam turbine
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....
. In these examples the "piston" is typically not cylindrical as in a modern internal combustion design, and is generally rectangular in cross-section as seen from the top, rotating in a flat disk "cylinder". From the side they are either flat plates or pie-wedge shaped. The term "swing-piston" is not entirely accurate in these cases, but the operating cycle is identical and is properly considered here.
The first known example was introduced by Elijah Galloway in 1829 for ship propulsion. It featured a single vane rotating through 270 degrees. It appears this version was never built, although a model still exists in the Science Museum
Science Museum (London)
The Science Museum is one of the three major museums on Exhibition Road, South Kensington, London in the Royal Borough of Kensington and Chelsea. It is part of the National Museum of Science and Industry. The museum is a major London tourist attraction....
. Galloway also designed a wide variety of pure rotary engines using vanes as well.
A more serious attempt was the "Cambrian System" of John Jones in 1941. This design used two or three flat plates that were geared to move closer or further apart as the cycled continued. When the plates were at their closest point, steam was admitted between them using a valve, pushing them apart as the cycle continued. When the plates reached their maximum distance, an internal passage was uncovered that allowed the partially-expanded steam to flow across the center of the device into the area on the other side of the vanes, which were now at their minimum distance. In this fashion the design was effectively a compound engine.
Many variations followed, and a number of these would see limited use in the field. Notable among them was John Ericsson
John Ericsson
John Ericsson was a Swedish-American inventor and mechanical engineer, as was his brother Nils Ericson. He was born at Långbanshyttan in Värmland, Sweden, but primarily came to be active in England and the United States...
's design of 1843, which powered the USS Princeton
USS Princeton (1843)
The first Princeton was the first screw steam warship in the United States Navy. She was launched in 1843, decommissioned in 1847, and broken up in 1849....
, the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
' first screw-powered steamship. Charles Parsons
Charles Parsons
Charles Parsons may refer to:* Charles Algernon Parsons , British engineer known for his invention of the steam turbine* Charles Parsons , professor in the philosophy of mathematics at Harvard University...
also examined the concept and appears to have produced two swing-piston engine designs before moving on to the steam turbine
Steam turbine
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....
. The Roots brothers also designed a swing-piston engine of a unique type, although they are better known for their supercharger design.
Internal combustion
It is unclear whether or not any internal combustion swing-piston engine has ever reached production, but the closest attempt appears to be the GermanGermany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
-era design by Otto Lutz. His design had six pistons in total, three each attached to two disks. The disks were geared to each other to form six chambers between the pistons, such that at any one time one set of three chambers were "close together" while the other set of three was "wide apart", varying between those two extremes as the disks rotated. The timing was arranged such that the chambers reached their "close together" point over the spark plug, and their "wide apart" point over the intake and exhaust ports. This action is similar to the Wankel, the primary difference being that Wankel creates compression and expansion via the shaping of the engine and rotor, as opposed to the relative motion of the pistons.
Lutz's engine was being designed as an experimental gas generator
Gas generator
A gas generator usually refers to a device, often similar to a solid rocket or a liquid rocket that burns to produce large volumes of relatively cool gas, instead of maximizing the temperature and specific impulse. The low temperature allows the gas to be put to use more easily in many...
for a new type of aircraft engine
Aircraft engine
An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines...
, one that replaced a traditional centrifugal
Centrifugal compressor
Centrifugal compressors, sometimes termed radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery.The idealized compressive dynamic turbo-machine achieves a pressure rise by adding kinetic energy/velocity to a continuous flow of fluid through the rotor or impeller...
or axial compressor
Axial compressor
Axial compressors are rotating, airfoil-based compressors in which the working fluid principally flows parallel to the axis of rotation. This is in contrast with other rotating compressors such as centrifugal, axi-centrifugal and mixed-flow compressors where the air may enter axially but will have...
with his swing-piston design. Ultimately the exhaust would be used to drive a turbine, that power being used to drive a propeller
Propeller
A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's...
to produce a turboprop
Turboprop
A turboprop engine is a type of turbine engine which drives an aircraft propeller using a reduction gear.The gas turbine is designed specifically for this application, with almost all of its output being used to drive the propeller...
. For this role the exhaust gas was too hot to be used directly in a turbine, given the available materials, so the engine featured a second "exhaust port" that vented cold pressurized air, which was then mixed into the hot exhaust. For direct power use, as opposed to driving a turbine, this "third area" of the engine can simply be left open to the air to avoid losing power to compression that will not be used.
The initial test engines had some minor problems, notably with sealing, but these were worked through and the engines were under test during 1944. One particularly nice feature of swing-piston engines is that they can be bolted back to back along a common crank shaft to make a larger engine, and with each additional stage the running becomes smoother and the only part that needs to be made larger is the crankshaft. A similar arrangement with a radial engine
Radial engine
The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders point outward from a central crankshaft like the spokes on a wheel...
is generally more difficult to arrange, especially cooling, and ones with inline engine
Straight engine
Usually found in four- and six-cylinder configurations, the straight engine, or inline engine is an internal-combustion engine with all cylinders aligned in one row, with no offset...
arrangements soon become so long that keeping the crankshaft from vibrating becomes a serious problem (see Chrysler IV-2220 for example).
Each "cylinder" from Lutz's design was 0.70 m in diameter and only about 30 cm in depth, providing 445 hp from 140 kg, an excellent power-to-weight ratio
Power-to-weight ratio
Power-to-weight ratio is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement of actual performance of any engine or power sources...
compared even to jet engines of the era. A five-block version was proposed for his turboprop concept, providing 3,450 hp from an engine about 2 m long. While the power-to-weight was good, the density of the engine was simply superb.
The overall turboprop looked much more like a jet engine than a piston one. The swing-piston gas generator was located in the middle of a long nacelle, with a five-stage axial compressor in front and a three-stage turbine behind. The compressor was used both to act as a supercharger
Supercharger
A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...
for the piston engine, as well as provide cold air to cool the turbine. The actual power to the propeller, combining both the pistons and the turbines, was 4,930 hp at 10,000 m altitude, far greater than any German wartime project.
Why all this complexity to produce a new version of an engine, the turboprop, whose primary advantage was simplicity? The main problem with conventional jet engines is that the combustion takes place in an open chamber, which is considerably less efficient than the closed chamber of a piston engine, where it has constant volume (or close to it). The Otto cycle
Otto cycle
An Otto cycle is an idealized thermodynamic cycle which describes the functioning of a typical reciprocating piston engine, the thermodynamic cycle most commonly found in automobile engines....
or Diesel cycle
Diesel cycle
The Diesel cycle is the thermodynamic cycle which approximates the pressure and volume of the combustion chamber of the Diesel engine, invented by Rudolph Diesel in 1897. It is assumed to have constant pressure during the first part of the "combustion" phase...
used in piston engines has a much lower specific fuel consumption than the Brayton cycle
Brayton cycle
The Brayton cycle is a thermodynamic cycle that describes the workings of the gas turbine engine, basis of the airbreathing jet engine and others. It is named after George Brayton , the American engineer who developed it, although it was originally proposed and patented by Englishman John Barber...
of a traditional gas turbine engines at low speed. Lutz's design was intended to power very long-range bomber
Bomber
A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...
s and patrol aircraft, where fuel economy was more important than simplicity and outright performance.
Lutz later patented the design under "Rotary compressor and other engines", United States Patent 2,301,667.
Other examples
Lutz's design is not the only way to produce such an engine, BMWBMW
Bayerische Motoren Werke AG is a German automobile, motorcycle and engine manufacturing company founded in 1916. It also owns and produces the Mini marque, and is the parent company of Rolls-Royce Motor Cars. BMW produces motorcycles under BMW Motorrad and Husqvarna brands...
experimented with a traditional engine with poppet valve
Poppet valve
A poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The shaft guides the plug portion by sliding through a valve guide...
s on the combustion chambers, which had been used a number of times previously in experiments. Another approach entirely is to recover some of the heat of the exhaust in a heat exchanger
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...
and use that instead of fuel to heat the compressed air, a concept used by General Motors
General Motors
General Motors Company , commonly known as GM, formerly incorporated as General Motors Corporation, is an American multinational automotive corporation headquartered in Detroit, Michigan and the world's second-largest automaker in 2010...
in a series of automobile turbines. Generally, however, improvements in the basic piston engine in "low power" roles have kept any of these advanced designs out of the marketplace.
More recently, starting in the 1990s, a number of inventors have re-introduced the concept as if it were new. Examples include Angel Labs' "Massive Yet Tiny" engine, the Rotoblock, the Roundengine, the Trochilic Engine and designs by Tschudi and Hoose.
In 2009 Russian billionaire industrialist Mikhail Prokhorov
Mikhail Prokhorov
Mikhail Dmitrievitch Prokhorov is a Russian billionaire entrepreneur and owner of the American basketball team, the New Jersey Nets. After graduating from the Moscow Finance Institute he made his name in the financial sector and went on to become one of Russia's leading industrialists in the...
announced his plans to enter an automotive business with a series of a lightweight hybrid vehicle
Hybrid vehicle
A hybrid vehicle is a vehicle that uses two or more distinct power sources to move the vehicle. The term most commonly refers to hybrid electric vehicles , which combine an internal combustion engine and one or more electric motors.-Power:...
s utilizing this design as their prime mover
Engine
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...
. Another recent introduction aimed at the hybrid market is the "Hüttlin Kugelmotor", which combines the swing-piston concept with a modified swashplate
Swashplate
A swashplate is a device used in mechanical engineering to translate the motion of a rotating shaft into reciprocating motion, or to translate a reciprocating motion into a rotating one to replace the crankshaft in engine designs.- Construction :...
to produce a spherical design that directly powers an internal electrical generator
Generator
Generator may refer to:* Electrical generator* Engine-generator, an electrical generator, but with its own engine.* Generator , any of several closely related usages in mathematics.Computing:...
.
External links
- http://archive.aztrib.com/Repository/getimage.dll?path=EVT/2003/03/24/37/Img/Pc0370800.jpg
- http://www.youtube.com/watch?v=WNh7hBhvDXU
- http://www.youtube.com/watch?v=AM335uWoYBQ (toroidal engine from Franky Devaere)