Mainly a cylinder, the cylinder movement to the right end, open the right inlet valve to the right side of the cylinder high-pressure steam, open the left exhaust valve, high-pressure water vapor to push the piston to the left, the movement of the left end, open the left inlet valve to close the right side of the exhaust valve, to the left of the cylinder high-pressure water vapor to the left side of the cylinder, so that the piston of the cylinder to the right movement. The reciprocating motion of the cylinder piston is converted into rotary motion by the crankshaft of the coupling rod slider. The switch of each valve is also driven by the linkage slider slide valve. Commonly found in old steam locomotives (trains), which were eliminated due to low efficiency, burning coal ash and pollution.
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The steam engine is a reciprocating power machine that converts the energy of steam into mechanical work. The advent of the steam engine had caused the industrial revolution in the 18th century. It remained the world's most important prime mover until the beginning of the 20th century, when it gradually gave way to the internal combustion engine and the steam turbine, among others.
The end of the 16th century to the late 17th century, Britain's mining industry, especially coal mines, has developed to a considerable scale, relying on manpower and animal power has been difficult to meet the requirements of the removal of groundwater from the mines, and there is an abundance of cheap coal on site as fuel. The reality of the need to prompt many people, such as the British Papan, Savery, Newcomen, etc. is committed to the "fire water" exploration and experimentation.
Saffrey made the world's first practical steam water lifting machine, in 1698 to obtain the British patent labeled "Friends of the miners. He filled an egg-shaped container with steam, then closed the inlet valve and sprayed cold water outside the container to condense the steam and create a vacuum. Open the water inlet valve, the bottom of the mine by the atmospheric pressure of the water intake pipe into the container; close the water inlet valve, re-open the steam valve, relying on the steam pressure will be in the container of water through the drain valve pressure out. To be emptied of water in the container and filled with steam, close the inlet valve and drain valve, re-spray water to make the steam condensation. This cycle is repeated, working alternately with two egg-shaped containers, which can be continuously drained.
Saffrey's water lifter relied on the suction of the vacuum to draw water, which could not be drawn deeper than six meters. In order to draw water from dozens of meters deep mine, the water machine must be installed in the depth of the mine, with a higher steam pressure to press the water to the surface, which is undoubtedly difficult and dangerous at that time.
Newcomen and his assistant, Caley, invented the atmospheric steam engine in 1705 to drive a separate water pump, known as the Newcomen atmospheric steam engine. This steam engine first in the United Kingdom, and later on the European continent has been rapidly spread, and its modified products until the early 19th century is still manufacturing. Newcomen atmospheric steam engine thermal efficiency is very low, this is mainly due to the steam into the cylinder, in the cylinder wall has just been cooled by the water condensation and the loss of a lot of heat, only in the low-cost coal-producing areas have been popularized.
In 1764, the British instrument repairer Watt for the University of Glasgow to repair the model of the Newcomen steam engine, noticed this shortcoming, and in 1765 invented a steam engine with a condenser separate from the cylinder wall, and in 1769 obtained a British patent. The initial Watt steam engine still used the balance lever and lever mechanism to drive the pump, in order to remove condensate and air from the condenser, Watt installed a pump. He also added a sandwich to the outer cylinder wall and heated the cylinder wall with steam to reduce condensation losses.
Before and after 1782, Watt further improved the machine, the completion of two important inventions: in the live cold halfway through the working stroke, close the inlet valve, so that the steam expansion of the work to improve the thermal efficiency; so that the steam in the piston on both sides of the work (double-action type), in order to improve the output power. At this time the piston both downward pulling lever and upward push lever, fan-shaped balance lever and zipper is no longer applicable, Watt made the invention of the parallelogram mechanism. Watt also used the crank linkage mechanism in steam engines in the late 18th century.
Watt's creative work to make the rapid development of the steam engine, he made the original can only lift the water of the machinery, became a steam engine can be universally applied, and make the thermal efficiency of the steam engine exponentially increased, coal consumption greatly reduced. Therefore, Watt is the most important inventor of the steam engine.
Since the late 18th century, the steam engine has been widely used not only in the mining industry, but also in smelting, textiles, machine building and other industries, all of which have gained rapid popularity. It made Britain's textile production in more than 20 years (from 1766 to 1789) increased five times, providing the market with a large number of consumer goods, accelerated the accumulation of capital, and put forward urgent requirements for the transportation industry.
The experiment of using steam engine as propulsion power in ships began in 1776, after continuous improvement, to 1807, the United States of America, Fulton made the first practical open-wheel propulsion steam engine ship "Claremont". Since then, the steam engine in the ship as a propulsion power for more than a hundred years.
In 1801, Britain's Trevithick put forward the concept of mobile steam engine, in 1803, the use of track mobile steam engine first appeared in the coal mines, which is the prototype of the locomotive. The British Stephenson will continue to improve the locomotive, in 1829 created the "Rocket" steam locomotive, the locomotive towing a carriage containing 30 passengers, speed of 46 km / h, attracted the attention of countries, the beginning of the railroad era.
The end of the 19th century, with the rise of electric power applications, the steam engine was once as the main power plant in the power plant. 1900, the United States, New York, there was a single power of up to five megawatts of steam engine power station.
The development of the steam engine reached its peak in the early 20th century. It has a constant torque, variable speed, reversible, reliable, easy to manufacture and maintain and other advantages, so it was widely used in power stations, factories, locomotives and ships and other fields, especially in warships became the only prime mover.
Steam engines can be divided into single-acting and double-acting according to the steam working on one or both sides of the piston; according to the arrangement of the cylinder, it can be divided into vertical and horizontal; according to the expansion of the steam in a cylinder or sequentially expand in a number of cylinders, it can be divided into single-expansion type and multi-expansion type; according to the direction of flow of steam in the cylinder, it can be divided into reflux and single-flow; according to the way of steam discharge and steam pressure can be divided into condensing, atmospheric and back-pressure type. The steam discharge and discharge pressure can be divided into condensing type, atmospheric type and back-pressure type.
The simple steam engine consists of a cylinder, a base, a piston, a crank linkage mechanism, a slide valve steam distribution mechanism, a speed regulating mechanism and a flywheel, etc. The cylinder and the base are stationary parts. New steam from the boiler, through the main steam valve and throttle valve into the slide valve chamber, controlled by the slide valve alternately into the left or right side of the cylinder, pushing the piston movement.
The development of the steam engine was first reflected in the increase in power and efficiency, which in turn depended mainly on the improvement of steam parameters. Initial steam engine steam pressure is only 0.11 ~ 0.13 MPa, the early 19th century to reach 0.35 ~ 0.7 MPa, the 1920s was used to 6 ~ 10 MPa. In the steam temperature, the end of the 19th century is not more than 250 ℃, and to the 1930s had used 450 to 480 ℃.
As for efficiency, watt's early continuous operation of steam engines, according to the calorific value of fuel, the total efficiency of no more than 3%; to 1840, the best condensing steam engine total efficiency of up to 8%; to the twentieth century, the highest efficiency of the steam engine can reach more than 20%.
In terms of speed, the end of the 18th century, Watt steam engine only 40 ~ 50 rpm; the early 20th century, the speed of 100 ~ 300 rpm, individual steam engines have reached 2500 rpm. In terms of power, the initial power of a single engine only a few horsepower, the early 20th century, a marine steam engine power up to 25,000 horsepower.
With the improvement of steam parameters and power, steam has been impossible to continue to expand in a cylinder, but also must continue to expand in the connected cylinders, so the emergence of multi-stage expansion of the steam engine. Steam engine by the lubricating oil flash point limitations, the maximum temperature of the steam used are generally not more than 400 ℃, locomotives, ships and other mobile steam engines are slightly lower, most of them are not higher than 350 ℃. Taking into account the possibility of expansion and structural economy, commonly used pressure below 2.5 MPa. Steam parameters are limited, thus also limiting the further increase in the power of the steam engine.
The emergence and improvement of the steam engine to promote social and economic development, but at the same time the development of the economy in turn to the steam engine put forward higher requirements, such as the requirements of the steam engine power, high efficiency, light weight, small size, etc.. Although people have made many improvements to the steam engine, and constantly expand its scope of use and improve its performance, but with the development of steam turbines and internal combustion engines, steam engines due to the existence of insurmountable weaknesses and the gradual decline.
The weaknesses of the steam engine are: it cannot be separated from the boiler, the whole device is both bulky and huge; the pressure and temperature of the new steam can not be too high, the exhaust pressure can not be too low, it is difficult to improve the thermal efficiency; it is a kind of reciprocating machine, inertia force limits the speed of the speed of the increase; the work process is discontinuous, the flow of steam is limited, which will limit the power of the increase.
Therefore, the internal combustion engine, which discarded the bulky boiler, eventually replaced the steam engine in ships and locomotives with its light weight, small size, high thermal efficiency and flexible operation. Steam turbine, on the other hand, with its high thermal efficiency, high stand-alone power, high speed, light weight per unit of power and smooth operation and other advantages, the steam engine crowded out of the power station.
Then the electric motor and its ease of use, replacing the steam engine in industrial equipment. However, small power steam engine thermal efficiency than the turbine, so in the coal-producing areas or only poor quality fuel areas or some special occasions, the steam engine still has a role to play.
The steam engine has had a great historical role in advancing mechanical industry and even society. With its development and the establishment of thermodynamics and mechanics for the development of steam turbines and internal combustion engines laid the foundation; steam turbine inherited the steam engine to steam as a work material, and the use of condenser to reduce the exhaust pressure of the advantages, discarded the reciprocating motion and the shortcomings of the intermittent steam feed; internal combustion engine inherited the basic structure of the steam engine and the transmission form, the use of fuel oil will be fed directly into the cylinder combustion mode, the formation of a Much higher thermal efficiency of the thermal cycle; at the same time, the steam engine used in the cylinder, piston, flywheel, fly hammer governor, valves and seals, etc., are composed of a variety of modern machinery, the basic components.