A vacuum engine refers to any kind of engine which derives its force from air pressure against one side of the piston, while also having a partial vacuum on the other side of it. This pressure differential can be the result of heat transfer, or mechanically produced by an external source.
Some early gas engines worked on the "vacuum" or "atmospheric" principle in a similar way to the Newcomen steam engine. A mixture of gas and air was eaten by the cylinder and ignited; the mixture expanded and part of it escaped through the exhaust valve; the valve then closed, the mixture cooled and contracted, and atmospheric pressure pushed the piston in. Such engines were very inefficient and were superseded by engines working on the Otto cycle.
(also called flame-licker engine, flame-engine, or flame-dancer)
At the beginning of an intake stroke, a valve in the head of the cylinder opens and admits a charge of burning gas and air, which is trapped by the closing of the valve and expands. Towards the end of the stroke the charge comes into contact with a water- or air-cooled part of the cylinder and is chilled, causing a sudden drop in pressure sufficient to suck the piston – which is open towards the crank – back on the return stroke. The valve opens again in time for the piston to expel the burnt gases before the next stroke begins.
In a vacuum motor, the partial vacuum is created by an external pump. These motors were commonly used to power railway turntables in the UK, using vacuum created by a steam locomotive's vacuum brake ejector. The operating principle is similar to a steam engine – in both cases power is extracted from a difference in pressure. [lower-roman 1]
Small vacuum motors were also used to operate windscreen wipers in automobiles. In this case, the motors were powered by manifold vacuum. This arrangement was not very satisfactory because, if the throttle were wide open, the wipers would slow down, or even stop. Modern automobiles use electrically powered wipers. Modern automobiles still use a vacuum motor of a kind, however, the vacuum servo. Brakes are operated by a hydraulic system, but they use a ‘vacuum motor’ to amplify the force provided by the driver. Small vacuum motors were also used from the late 1960s to control servomechanisms such as door locks, [lower-roman 2] heater controls [lower-roman 3] or movable bonnet ventilation flaps. [lower-roman 4]
Some Player piano use vacuum engines.
You could say that the global Industrial Revolution arose because of a 'vacuum motor', because all the early steam engines, especially the pioneering Boulton and Watt engines, operated with almost atmospheric pressure steam. You can easily make a demonstration vacuum engine using a flywheel, simple plumbing parts and a few other simple components, as Neil A Downie shows in the reference.
A vacuum system can be used for power transmission, although the maximum power that can be transmitted to a vacuum motor is less than conventional pneumatics. There is an optimum pressure for the operation of a vacuum power transmission system, of around 0.4 bar (8 psig), as Downie also shows. Although less efficient than pneumatics, it can be perfectly workable. For example, a 22 mm (7/8") pipe on vacuum can transmit as much power on 0.4 bar (8 psig) as a 6 mm (1/4") pipe on 8 bar (100 psig). The system is efficient enough that Boulton and Watt used vacuum power transmission in their factory. They called the vacuum main in the factory the ‘spirit pipe’. [1] [2]
Unlike the ideal Otto cycle engine, the vacuum engine relies on a constant heat source provided by burning fuel. As mentioned above, a valve allows an intake of heat into the piston chamber. Estimating the heat in or Qin is constant in the controlled volume space, the ideal gas equation PV = nRT implies an increase in the pressure of the piston chamber. After the valve closes, the piston undergoes an adiabatic process during the downward stroke. Once the piston reaches the bottom of its stroke, the chamber is cooled either by the surrounding air or water, and the resulting Qout forces the pressure in the piston to decrease. The system then undergoes another adiabatic compression of the gas in the chamber, which is subsequently released by the valve at the top of the cylinder's stroke, while simultaneously allowing new heated gas to enter the chamber.
One of the major issues that this engine encountered while being developed was that the efficiency of this model was extremely poor in real applications. Because the heat source is not contained to a specific area, only a small portion of the potential fuel is being consumed to power the engine. Because Engine efficiency is defined by the relationship between the amount of work done and the potential energy in the fuel consumed, it can be seen that in the vacuum engine only a small amount of the burning fuel is being used to power the engine. The rest of the fuel energy is lost to the surrounding atmosphere.
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.
An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.
A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common features of all types. The main types are: the internal combustion engine, used extensively in motor vehicles; the steam engine, the mainstay of the Industrial Revolution; and the Stirling engine for niche applications. Internal combustion engines are further classified in two ways: either a spark-ignition (SI) engine, where the spark plug initiates the combustion; or a compression-ignition (CI) engine, where the air within the cylinder is compressed, thus heating it, so that the heated air ignites fuel that is injected then or earlier.
A steam engine is a heat engine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a cylinder. This pushing force can be transformed, by a connecting rod and crank, into rotational force for work. The term "steam engine" is most commonly applied to reciprocating engines as just described, although some authorities have also referred to the steam turbine and devices such as Hero's aeolipile as "steam engines". The essential feature of steam engines is that they are external combustion engines, where the working fluid is separated from the combustion products. The ideal thermodynamic cycle used to analyze this process is called the Rankine cycle. In general usage, the term steam engine can refer to either complete steam plants, such as railway steam locomotives and portable engines, or may refer to the piston or turbine machinery alone, as in the beam engine and stationary steam engine.
A carburetor is a device used by a gasoline internal combustion engine to control and mix air and fuel entering the engine. The primary method of adding fuel to the intake air is through the Venturi tube in the main metering circuit, though various other components are also used to provide extra fuel or air in specific circumstances.
A two-strokeengine is a type of internal combustion engine that completes a power cycle with two strokes of the piston in one revolution of the crankshaft. A four-stroke engine requires four strokes of the piston to complete a power cycle in two crankshaft revolutions. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust functions occurring at the same time.
In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in petrol/gasoline, diesel engines and some hydrogen engines. EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. The exhaust gas displaces atmospheric air and reduces O2 in the combustion chamber. Reducing the amount of oxygen reduces the amount of fuel that can burn in the cylinder thereby reducing peak in-cylinder temperatures. The actual amount of recirculated exhaust gas varies with the engine operating parameters.
The atmospheric engine was invented by Thomas Newcomen in 1712, and is often referred to as the Newcomen fire engine or simply as a Newcomen engine. The engine was operated by condensing steam drawn into the cylinder, thereby creating a partial vacuum which allowed the atmospheric pressure to push the piston into the cylinder. It was historically significant as the first practical device to harness steam to produce mechanical work. Newcomen engines were used throughout Britain and Europe, principally to pump water out of mines. Hundreds were constructed throughout the 18th century.
The Watt steam engine design became synonymous with steam engines, and it was many years before significantly new designs began to replace the basic Watt design.
A four-strokeengine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:
The Brayton cycle, also known as the Joule cycle, is a thermodynamic cycle that describes the operation of certain heat engines that have air or some other gas as their working fluid. It is characterized by isentropic compression and expansion, and isobaric heat addition and rejection, though practical engines have adiabatic rather than isentropic steps.
Main components found on a typical steam locomotive include:
An inlet manifold or intake manifold is the part of an internal combustion engine that supplies the fuel/air mixture to the cylinders. The word manifold comes from the Old English word manigfeald and refers to the multiplying of one (pipe) into many.
Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere.
A Cornish engine is a type of steam engine developed in Cornwall, England, mainly for pumping water from a mine. It is a form of beam engine that uses steam at a higher pressure than the earlier engines designed by James Watt. The engines were also used for powering man engines to assist the underground miners' journeys to and from their working levels, for winching materials into and out of the mine, and for powering on-site ore stamping machinery.
Engine efficiency of thermal engines is the relationship between the total energy contained in the fuel, and the amount of energy used to perform useful work. There are two classifications of thermal engines-
The term six-stroke engine has been applied to a number of alternative internal combustion engine designs that attempt to improve on traditional two-stroke and four-stroke engines. Claimed advantages may include increased fuel efficiency, reduced mechanical complexity, and/or reduced emissions. These engines can be divided into two groups based on the number of pistons that contribute to the six strokes.
A plenum chamber is a pressurised housing containing a fluid at positive pressure. One of its functions is to equalise pressure for more even distribution, compensating for irregular supply or demand. It is typically relatively large in volume and thus has relatively low velocity compared to the system's other components. In wind tunnels, rockets, and many flow applications, it is a chamber upstream on the fluid flow where the fluid initially resides. It can also work as an acoustic silencer.
Internal combustion engines come in a wide variety of types, but have certain family resemblances, and thus share many common types of components.
An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance, transforming chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to.
