A steam engine is (in the narrower sense) a piston heat engine . In a steam generator , which is part of the machine, it generates steam through combustion and converts the thermal energy contained in the steam (also pressure energy ) into mechanical work using pistons . Steam engines are heat engines with "external combustion", which distinguishes them from internal combustion engines .
A steam engine (in the broader sense) can also be understood colloquially as any other machine that is directly or indirectly driven by steam. These are both prime movers such as the steam turbine and steam-driven machines . Sometimes steam-powered transport and means of transport, agricultural machinery and even some devices are also referred to as steam engines.
The first functional steam engine from Thomas Newcomen was used from the beginning of the 18th century in hard coal mining for dewatering , where they initially used older mechanical power sources such as B. added water wheels and later replaced them. After gradual improvements in efficiency, it was worthwhile towards the end of the 18th century to use them in the growing textile industry to drive textile machines , and they finally spread to other branches of industry, where they also supplemented water and windmills . A decisive improvement was achieved by James Watt , who received a patent for it in 1769. In the course of the 19th century, they played an important role in transportation, especially for driving steam ships and steam locomotives . Its use as a locomobile was also not insignificant . After initial success, its application in steam automobiles and trucks lost its importance and is practically non-existent today. The same applies to the field of steam tractors and locomobiles, where steam propulsion dominated before 1900. The first airship was also powered by a steam engine in 1852. At the turn of the 20th century, the steam engines were generally replaced by the electric motor and, as vehicle propulsion, by the internal combustion engine . To this day, steam turbines are still used in power plants to generate electrical energy.
The following article only deals with piston engines (steam engines “in the narrower sense”).
How a piston steam engine works
The piston steam engine converts thermodynamic energy (steam pressure) from steam generators into mechanical rotational energy. A piston moves back and forth in the associated cylinder , it performs an oscillating movement. However, a rotational movement is usually required for the useful mechanical energy .
The forward movement of the piston is carried out with the pressure of the steam as a working cycle . When the piston is loaded on one side, the return movement is carried out from stored rotational inertia. In contrast, when the piston is acted upon on both sides, the return movement of the piston is also performed as a working cycle, now on the underside of the piston by means of steam pressure control.
A slide controls the supply of steam into the cylinder . With the pressure, the piston is first shifted downwards or in the direction of the crankshaft . The linear movement of the piston is converted into a rotational movement by means of a crosshead and connecting rod as a coupling link on the crank pin of the crankshaft . The connecting rod then pushes (in one-sided operation) with the rotational energy stored in the flywheel and in the crankshaft, the piston linearly from the lower position back to its upper starting position.
The working process of a steam engine is thus divided into two cycles and is therefore a two-cycle process .
Atmospheric steam engine
In an atmospheric steam engine , the cylinder space under the piston is filled with water vapor . In the next work cycle, water is injected into the cylinder so that the water vapor cools down and condenses . A negative pressure is generated so that the piston is pressed into the cylinder by the external atmospheric pressure. The extending movement of the piston takes place when the steam valve is open and by means of a flywheel attached to a lever arm, the so-called balancer.
The best-known representative of this design was the atmospheric steam engine from Thomas Newcomen from 1712. The steam engine was mainly used for dewatering in coal mines. The energy efficiency of this machine was below 1% until it was further developed by James Watt . Watt moved the condensation of the steam from the working cylinder into a downstream water-cooled container, the condenser. As a result, the constant cooling and renewed heating of the working cylinder in each work cycle, a cause of considerable energy losses, was eliminated.
The figure on the right shows how the negative pressure or the atmospheric pressure in the atmospheric steam engine does the work when the hot steam condenses and contracts strongly. Mainly liquid water emerges from the cylinder . This way of working is not very economical because a lot of energy is used to heat the cylinder and piston with each stroke and then to cool them down again. In order to let the steam condense quickly enough, cold water was injected into the cylinder near top dead center (not shown here).
In the expansion steam engine , the filling valve opens only briefly at the beginning of the work cycle. In contrast to the full-pressure machine , the steam that has flown in under high pressure loses part of its pressure during the work cycle. This also leads to a cooling of the cylinder, but significantly less steam is consumed than with the full printing machine . In order to limit the cooling, the steam is not completely expanded to atmospheric pressure. Compound steam engines also use the pressure remaining when the steam exits by directing the steam into another cylinder with a larger diameter. (Note: Contrary to what is shown here, the steam hardly cools any further during the downward movement of the piston.)
Low pressure steam engine
In the case of the low-pressure steam engine, the steam is applied with a slight excess pressure of a few 100 mbar. In contrast to the Newcomen steam engine, work is not only done during condensation, but also during filling of the cylinder. This leads to an increase in performance and was the starting point for the further development of the steam engine towards higher steam pressures. The best-known representatives of this design were the steam engines by James Watt from around 1769 (see below).
Watt also developed the "single-acting" steam engine, which only acts on the piston from one side, into the "double-acting" steam engine, in which the piston is alternately acted upon from the top and bottom. This resulted in a reduction in weight and also increased efficiency and performance to a certain extent, since the idle stroke was eliminated. The expansion machine , in which steam only flows in at the beginning of a stroke, which then expands and exits the cylinder at lower pressure, was a further development of the low-pressure steam engine and brought a further increase in efficiency compared to the full-pressure machine , which receives full steam pressure during the entire stroke.
High pressure steam engine
In high-pressure steam engines, the steam is heated to well over 100 ° C, so that a higher pressure builds up. There is no need to cool the water vapor emerging from the cylinder, since the atmospheric pressure is no longer significant compared to the significantly higher operating pressure (exhaust mode). The condenser can therefore be omitted, which, in conjunction with the higher energy density of the pressurized steam, makes this type of machine considerably lighter and thus made the use of steam engines in steam locomotives possible in the first place. Practically all piston steam engines in vehicles since Oliver Evans and Richard Trevithick from around 1802 (see below) are representatives of this design .
Compound steam engine
A compound steam engine or multiple expansion engine is a steam engine with at least two working units connected one after the other in the steam direction.
History of the steam engine
Pre-industrial steam engines
The history of the steam engine goes back to the first century AD - the first report on a technical, rudimentary “steam engine” device, the Heron's ball (also called aeolipile or aeol ball ), comes from the pen of the Greek mathematician Heron of Alexandria . In the centuries that preceded the first modern steam engines, steam powered "machines" were mainly built for demonstration purposes, to illustrate the principle of steam power. The first attempts at a steam engine came from Blasco de Garay in 1543, de Caus in 1615 and the Italian Branca in 1629.
Major advances were made by Denis Papin , among others, in 1690 with the invention of the safety valve and the Papin pot. Thomas Savery's steam pump from 1698 is believed to be the first practical application of steam. However, due to their low level of efficiency, they were all without resounding economic success.
The first usable steam engine was designed by Thomas Newcomen in 1712 and was used to raise water in mines . This so-called atmospheric steam engine created a negative pressure in relation to the atmosphere by injecting water into a cylinder filled with steam. With this pressure difference, the piston was pressed down by the atmospheric air pressure in the working cycle and then pulled up again into the starting position by the weight of the pump rod to be driven. The power transmission between the piston rod and the balancer was carried out by means of a chain . The efficiency of the Newcomen's machine was 0.5 percent and limited its application to mines alone.
In 1720 Jacob Leupold , Mathematico and Mechanico in Prussia and Saxony, described a high-pressure steam engine with two cylinders. The invention was published in his major work Theatri Machinarum Hydraulicarum Tomus II. The machine used two lead-loaded pistons that provided their continuous movement to a water pump. Each piston was lifted by the steam pressure and returned to its original position by its own weight . The two pistons shared a common four-way valve which was directly connected to the steam boiler .
Watt's steam engine
James Watt , who is often wrongly credited with the invention of the steam engine, improved the efficiency of the Newcomer steam engine considerably. With his design, patented in 1769 and built six years later by John Wilkinson, he shifted the cooling process out of the cylinder into a separate condenser . In this way, Watt was able to dispense with the atmospheric return of the piston and let the machine do work on both piston strokes.
Watt's parallelogram , which he invented , ensured the straight up and down movement of the piston rod in these single-acting steam engines. Both Newcomens and Watts steam engines originally only had upright cylinders, which merely deflected the up and down movement of the piston via a balancer in order to transfer it into the shaft on the sump rod . In 1781 Watt patented a planetary gear set in his name, designed by the chief engineer at Boulton & Watt , William Murdoch , to transform the movement of the piston and thus make the machine turn a flywheel . The use of a crank drive was not possible in England due to a patent held by James Pickard. The planetary gear is a much more complex solution to the problem of converting a straight into a rotating movement, but on the other hand it had the advantage that it was simultaneously possible to increase or decrease the speed.
James Watt is considered to be the discoverer of the benefits of steam expansion . In the steam engine, this effect is achieved by closing the valves prematurely ; this interrupts the supply of steam to the cylinder while the steam trapped therein continues to work . Later Watt's steam engines were double-acting, the piston was alternately supplied with steam from one side and the other. The outlet to the condenser was on the opposite side.
Thanks to these improvements, the Watt steam engine saved a multiple of the thermal energy required to operate the machine compared to its predecessors. The efficiency of the Watt machine finally reached 3 percent. To demonstrate the ability of his steam engines, Watt invented the unit of horsepower . With his commercial partner Matthew Boulton , however, he did not sell his machines, but made them available to his customers in order to have part of the saved fuel costs paid off. This gave birth to an early form of contracting .
With these developments and further technical improvements, steam engines became economical from the second half of the 18th century - at least in coal mining. Even though other areas of application in industry and transport gradually opened up, it was not until the 1860s that steam engines were used on a massive scale in England. In other countries such as France and the USA, where hydropower was a strong competitor, the final breakthrough of the steam engine came a little later.
High pressure and superheated steam
A high pressure steam engine was designed by Oliver Evans in 1784 . The first copy was not built by him until 1812. Before that came Richard Trevithick , who installed the first high-pressure steam engine in a road vehicle in 1801. The prerequisite for the functionality of high-pressure steam machines was the progress made in metal production and processing at that time, because the machine parts in high-pressure machines have to fit very precisely. There was also the risk of the boiler exploding.
The continuous further development of the pressure-operated steam engine, which initially worked with so-called " saturated steam ", led from the single-cylinder superheated steam engine to the two- or three-cylinder compound machine and finally to the multi-cylinder superheated steam high-pressure steam engine as offered by Kemna . In the case of the saturated steam machine, all boiler pipes for generating steam are located in the water bed; the superheated steam machine has a second pipe system that is brushed by the fire or the hot flue gases. As a result, the steam is “overheated” and reaches temperatures of around 350 degrees Celsius. The compound machine or compound machine has a high-pressure cylinder with a small bore and one or more low-pressure cylinders connected in series. The now partially expanded and cooler escaping steam, which is fed into the high-pressure cylinder as superheated steam, still has enough work capacity to operate the low-pressure cylinder, which has a much larger bore. An attempt is made to coordinate the cylinder bores so that the torque generated by both cylinders on the crankshaft is approximately the same. The volume of both cylinders must also be matched to the speed of the steam engine so that the expansion of the steam is distributed over both cylinders. Kemna started building steam engines with two high pressure cylinders from 1908.
In Prussia, attention was drawn to the "fire machines" from England as early as 1769. The senior consistorial councilor Johann Esaias Silberschlag in particular , who had also made a name for himself as a scientist, recognized the benefits of this machine at an early stage and prepared several extensive reports on it by 1771. In 1785 the first steam engine, which was replicated in Prussia, was put into operation near Burgörner . As early as 1778, James Watt had agreed to hand over his improved steam engine for lifting water to the Prussian mining authorities under professional guidance. His company Boulton & Watt , however, demanded a 14-year supply monopoly , a condition that mercantilist Prussia did not want to accept. Under the pretext of intending to buy, the Oberbergrat Waitz von Eschen and the assessor Carl Friedrich Bückling (1756–1812) were sent to England by the Prussian Minister Friedrich Anton von Heynitz . Waitz should specifically familiarize himself with the functionality of the machine and Kückling should prepare appropriate construction plans. Probably only an English steam engine was acquired and used in 1779 on a lignite mine near Altenweddingen .
After Bückling had been sent to England a second time, he was able to draw up exact construction plans for his own steam engine based on the Wattschen model with the assistance of the Prussian Academy of Sciences . A reduced, functional model was built by 1783, from then on the parts were manufactured and assembled in their original size. On August 23, 1785, the first German steam engine Wattscher was officially put into operation on the König-Friedrich-Schacht near Hettstedt . At first, the machine's susceptibility to failure earned it a lot of ridicule. By poaching the British steam engine mechanic William Richards, the problems in Hettstedt were eliminated by 1787. The machine became an economic success. In 1794 it was replaced by a stronger one and now placed on a coal mine near Löbejün , where it worked until 1848. A 1: 1 replica of this steam engine has been in the Mansfeld Museum in Hettstedt since 1985 and can be demonstrated in motion. In Tarnowitz , Upper Silesia , a steam engine was put into operation on January 19, 1788, which served to drain the Tarnowitz mines. This steam engine is falsely claimed to have been the first on mainland Europe.
The first steam engine of the Aachen district was in Eschweiler in 1793 and was also used there for dewatering in mining. In 1803, Franz Dinnendahl built the first steam engine in the Ruhr area in Essen . Two years earlier, Dinnendahl had already supervised the use of the first steam engine for dewatering in the Ruhr mining industry. Made in England, this was put into operation at the Vollmond colliery in Bochum- Langendreer.
Other German states
Around the same time in the Duchy of Saxony-Gotha , the first functional steam engine in Thuringia was built in a small vitriol mine near Mühlberg (Thuringia) by the future engineer lieutenant Carl Christoph Besser , who worked for the mine from 1763 to 1774, and it was in operation for weeks held, it served for the permanent pumping of the pit water and was kept running day and night by two stokers or machinists. The multi-talented Besser was later employed by Duke Ernst as an engineer and architect for the construction of the Seeberg observatory and other projects in Gotha and thus lost interest in mechanical engineering.
From these early beginnings to the widespread use of the steam engine in the economy, however, several decades passed. In 1836 the first German steam engine statistics were compiled for the Düsseldorf administrative region . Due to technical improvements, the incipient concentration of the emerging industry, increasingly exhausted hydropower potentials and the massive reduction in the cost of coal transport by rail, steam engines became more and more economically viable. According to incomplete statistics from 1846, there were 1,518 steam engines in the Zollverein . In 1861 the number had risen to 8695 pieces.
In the steel industry, steam engines were used, among other things, to drive fans, pumps and rolling mills. Two compactors with a maximum output of 10,000 HP, built in 1913 and 15,000 HP, built in 1911, worked reliably in the Maxhütte (Sulzbach-Rosenberg) until it was shut down in 2002. They were among the most powerful steam engines in the world.
Steam engines today
As a vehicle drive, steam engines have largely been replaced by internal combustion engines, which start without a warm-up time, have a higher degree of efficiency, offer greater power with less weight and are more convenient to operate. Furthermore, due to the comprehensive supply of electrical energy , the steam engine has lost its function as the central energy source of an industrial company , which it held for a long time. In hard coal mining, steam engines were and are still used in conveyor systems, because there the steam engine can serve both as a conveyor machine for lifting coal and as a brake for lowering backfill material . When braking, the energy is used to heat the steam.
Although the days of the piston steam engine seem to be long gone, a renaissance cannot be ruled out. One of its advantages over the internal combustion engine is its continuous combustion process, which can be designed with lower emissions . Another advantage of the steam engine is its extreme overload capacity when there is demand for power peaks . The closed circuit of steam and feed water that is customary today results in low-emission lubrication of the cylinder and piston of the machine. With this in mind, the steam engine was developed as a modernized steam engine .
On behalf of Volkswagen AG, IAV GmbH developed such a modern "steam engine" in the late 1990s, which generates a certain amount of high-pressure steam via extremely low-emission external combustion, which is then injected via nozzles, as in the diesel engine, depending on the energy requirement. At the end of 2000, the company Enginion emerged from this and further developed today's SteamCell from the ZEE prototype ( Zero Emission Engine ), which achieved an efficiency of 23.7% . This machine worked in the two-stroke process and also got by without the usual lubricants because the wear parts were made from modern carbon components. However, Enginion had to file for bankruptcy in 2005.
- Carnot process
- Area damage
- Kettle crack
- Composite effect
- Model steam engine
- Stirling engine
- History of production technology
- Technology in industrialization
- Technology in the Renaissance
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