The steam engine is an invention, whose most significant evolutions date from the 18th century. It is a Thermal engine with external combustion, it transforms the thermal energy which the vapor has water provided by one or of the Chaudière S in mechanical energy . Like first energy source of constructible and controllable mechanical origin by the Man (contrary to the energy of the water, the tides or the wind, who require special sites and that one cannot easily actuate with the request), it had an major importance at the time of the Industrial revolution. But at the 20th century, it was supplanted by the Turbine, the electric engine and the Engine spark-ignition .
History
The first work on the steam and its use goes back to the Antiquité : Héron of Alexandria conceived and built at 1st century a. J. - C. the éolipyle which, although regarded as a toy because of its low power, was not less one engine steam, with Réaction.
The 17th century had to be waited, so that the idea to use the power of the steam reappears. In 1601, Giambattista beyond Carried, then in 1615, Solomon de Caus describes a Pompe able to drive out the water of a container. Then in 1629 Giovanni Branea suggests the idea of Moulin S driven by the vapor and the year according to David Ramseye obtains a patent for a pump driven by an engine with fire. In 1663 Edward Somerset improves the project of Caus by equipping the room with vapor with a cooler, it builds a model of big size, but it dies before to have been able to practically apply its creation.
In 1698, Thomas Savery deposits a patent on a pump intended for the Mining, running on the vapor, directly inspired by work of Edward Somerset. Thereafter, it improves it in collaboration with Thomas Newcomen, grace inter alia to work of the French Denis Papin. This last, after having invented a prototype of Pressure-cooker, had had the idea of the piston, thus giving access to unsuspected powers hitherto. A first commercial model was used as of 1712 in the coal mines, close to Dudley, in the center of the England. These pumps functioned by producing a vacuum in a room closed where one makes condense vapor, thanks to a water jet. The valves of admission and exhaust, initially with hand drive operation, are automated by Henry Beighton, in 1718. These pumps quickly become current in all the wet mines of the Europe. They remain however very expensive with employment because the cylinder must be heated before each admission of vapor.
The Scot James Watt, who was born in shells in 1736 and who died in 1819 repaired a Newcomen engine in 1763, then seeks ideas of improvement to increase the effectiveness by it. Its reflections lead in 1765 to the idea of a condensing chamber for the vapor separated by a valve, idea on which it deposits a patent in 1769. It then starts to produce engines improved with the financing of Matthew Boulton.
It continues in parallel to seek ideas on and around its invention. In 1781 it develops the mechanical system making it possible to create a rotation movement starting from the rectilinear motion of the piston, which then enables him to design the cylinder with double action where the vapor involves the Piston, at the time of its rise and its descent. The power of the machine is strongly increased by it.
It formalizes also a possible use in 1784 by depositing a patent on a Locomotive with vapor, it invents a pressure gauge of the vapor in the Cylindre, and in 1788 a valve of power on which it uses then the idea of Boulton to employ a centrifugal governor to make the power produced constant independently of the variations of the production of vapor and requests of power at exit. It introduces also a new measuring unit of the power, the Horse power.
Some reproach him for having slowed down the development of the systems with high pressure functioning by the expansion of the vapor in which he did not believe, but preached by other inventors as Jonathan Hornblower who had to await the expiry of the Brevet S in 1800, after their prolongation in 1782. This last developed in 1781, a double combined cylinder where the vapor passes initially in a cylinder in which it pushes the piston before passing in a cylinder functioning according to the principle of the condensation which is equivalent to a system with double action. But its invention remains experimental without possible application because of the patents of Watt, and it is then necessary to await 1803 and Arthur Woolf to see it emerging finally. Combined with a new type of condenser designed by Edmund Cartwright which wraps the cylinder and the appearance of the Chaudière S producing of the vapor with high pressure, this will allow the manufacture of machines compact and powerful, necessary to a mobile use.
Principle and operation
Via a system of distributer slide valve, opening and closing lights, the vapor of water under pressure is sent at an end of a Cylindre, where it pushes a Piston. This last involves the rod which is articulated above, it is also fixed on the Stealing of Inertie in a excentré point of its axis of rotation, its movement thus causes a rotation of the wheel.Wheel sets out again a rod ordering the Tiroir admission and of exhaust. When the piston arrives at the end of the cylinder, the rod pushes back the drawer:
- In the case of the cylinder simple effect, the drawer closes again the Lumière of entry of the vapor and on the same side another light to let escape the vapor contained in the cylinder opens. The wheel, by the accumulated kinetic energy, continues to turn, thus pushing back the piston with the starting point.
- In a cylinder for double purpose, the drawer opens, moreover, one inlet opening for the vapor on other side, it pushes back the piston which continues its push on the wheel.
On this wheel one places a Courroie establishing an elastic connection with the pulley of entry of a machine transforming this movement into a specific work. To be usable industrially, this energy must generally be controlled so that the number of revolutions depends neither on the risks on heating, nor especially of the request of power at exit. It is there that intervenes the centrifugal governor developped at the point by Watt, which acts directly on the Vanne by which the vapor arrives of the Chaudière.
Technology and refinements
With the generalization of its employment, the steam engine will know a whole series of improvements intended to improve its effectiveness and its power, by using the increasingly important pressures provided by the Chaudière S.
Double action
The double action invented by Watt becomes of general employment, it allows a large profit of power by eliminating the phase where the piston behaves like a brake, this one is then driving with the outward journey and the return. On the engines functioning by the expansion of the vapor, it is alternatively thorough by the two expansion rooms which it delimits. The feeding system to drawer has then as a role to start either the food, or the exhaust for the two rooms.
Description of operation
The arrival and the exhaust of the vapor on the two sides of the cylinder are regulated by the distributer slide valve (6). The piston is connected to the stick , which via the driving rod transforms the back and forth pass into circular motion. This movement is transmitted to all the driving wheels thanks to the coupling rods. The adjustment of the distributer slide valve to reverse walk is carried out by means of the wheel of ordering of the screw of change of walk (8) which is in the driving cabin.Work of the distribution (model of Distribution Walschaert): It is by the drawer (6) that the vapor is allowed in the cylinder (7) and acts alternatively on each face of the piston. The stem of piston actuates the rod coupled with the train of driving wheels via the articulated stick (5). The coupled wheels all become driving. Via contre-manivelle (2) fixed with 90° of the driving crank, a rod makes oscillate the slide (1) of distribution into which the operating rod of drawer (3) slips. Coupled with the lever in advance (4), the displacement of the rod on the slide makes it possible to regulate the shift between displacements of the drawer and those of the piston. One can thus regulate the power ratio/speed of the engine and also change direction.
Multiple expansion
During the 19th century, the pressure available on the outlet side of the boilers increasing, one ends up using several cylinders of increasing size, where the vapor passes successively progressively from its Détente. One saw thus initially the machines with double expansion like the locomotive compound, then those with triple expansion respectively comprising two and three cylinders called rolls with high, average and low pressure. Both or three cylinders actuated a common driving shaft, an alternative comprised two cylinders with low pressure, the four cylinders being then arranged in a configuration in V.This technology was particularly important in the naval and railway applications, because it made it possible to re-use the majority of the water contained in the vapor, avoiding having to carry great water reserves, as the tanks which existed on fixed installations.
Single flood (uniflow)
Invented by Jacob Perkins in 1827, this model is characterized by the use of Soupape S and of camshafts just like the spark-ignition engines for the vapor circulation, it presents like main advantages, to avoid making pass the hot vapor and that slackened by the same site and to be more sparing out of vapor.
Rotary type
It is an alternative resulting from recent research on the Quasiturbine.
Giffard injector
One of the problems of the steam engine, it is to supply the new water boiler.The traditional methods called either upon a tank placed in height, or with a pump driven by the engine.
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