The steam engine is a reciprocating power machine, which converts the energy of steam into mechanical work. The appearance of the steam engine caused the industrial revolution in the18th century. Until the beginning of the 20th century, it was still the most important prime mover in the world, and then it gradually gave way to internal combustion engines and steam turbines.
A steam engine needs a boiler to boil water to produce high-pressure steam. This kind of boiler can use wood, coal, oil or natural gas or even combustible garbage as heat source. The expansion of steam pushes the piston to do work.
The first steam engine in the world was invented by Greek mathematician Herod of Alexandria in the 1 th century, which was the embryonic form of the steam engine.
About 1679, the French physicist Dennis Papen made the working model of the first steam engine after observing the steam escaping from his pressure cooker. Contemporary Samuel Moran also proposed the steam engine.
Thomas Seville made an early industrial steam engine in 1698, and Thomas Newcomen made an early industrial steam engine in 17 12. They all made their own contributions to the development of steam engines. 1807, robert fulton was the first to successfully use a steam engine to drive a ship. Using scientific theory, Watt gradually discovered the faults of this steam engine. From 1765 to 1790, he made a series of inventions, such as separate condenser, cylinder external insulation layer, piston lubricated with oil, planetary gear, parallel linkage mechanism, centrifugal governor, throttle valve, pressure gauge and so on. , make the efficiency of the steam engine to more than three times that of the original newcomen machine, and finally invented the industrial steam engine.
From the end of 16 to the end of 17, the British mining industry, especially coal mines, has developed to a considerable scale, and it is difficult to meet the requirements of pumping groundwater only by manpower and animal power, and there are abundant and cheap coal as fuel on site. The needs of reality have prompted many people in Britain, such as Papan, savery and newcomen, to devote themselves to the exploration and experiment of "lifting water by firepower".
The original vacuum steam engine was used to pump water from mines. Newcomen's steam engine introduced steam into the cylinder, then closed the valve and injected cold water into the cylinder, which caused a vacuum when the steam condensed. Air pressure on the other side of the piston pushes the piston. Insert a pole deep into the mine to drive the water pump. The motion of the piston of the steam engine is transmitted to the piston of the pump through this rod, and the water is pumped out of the well.
The first big improvement is to separate the cylinder from the condensing cylinder through the valve. Watt invented this improvement in Birmingham. This improvement has improved the efficiency of the steam engine. The next improvement is the automatic operation of the valve.
These early vacuum steam engines had limited efficiency, but were relatively safe, because their pressure was relatively low, and the machines contracted inward instead of exploding outward to prevent material damage. Their efficiency is limited by external air pressure, cylinder deformation, combustion and boiling efficiency and condensation capacity. The theoretical maximum efficiency is limited by the relatively low boiling temperature of water at ordinary atmospheric pressure. The use of high temperature and high pressure steam greatly improves the efficiency of steam engines. But this kind of steam engine is much more dangerous than vacuum steam engine. The explosion of boilers and machines caused many serious accidents. The safety valve has brought great improvement here. When the pressure is too high, the safety valve deflates and depressurizes. But the real guarantee of safety only depends on the experience and safety rules of construction, operation and maintenance.
The world's first practical steam pump made in savery won the British patent named "Friends of Miners" on 1698. He first filled an egg-shaped container with steam, then closed the steam inlet valve and sprayed cold water outside the container to condense the steam in the container to form a vacuum. Open the water inlet valve, and the water at the bottom of the mine is sucked into the container through the water inlet pipe under the action of atmospheric pressure; Close the water inlet valve, reopen the steam inlet valve, and use steam pressure to press the water in the container out through the drain valve. When the water in the container is drained and filled with steam, close the steam inlet valve and drain valve, and spray water again to condense the steam. In this way, the two egg-shaped containers work alternately and can continuously drain water.
The pumps in savery rely on vacuum suction to pump water, and the pumping depth cannot exceed six meters. In order to pump water from a mine tens of meters deep, it is necessary to install a water pump in the depth of the mine and use high steam pressure to pump water to the ground, which is undoubtedly difficult and dangerous at that time.
Newcomen and his assistant Cali invented the atmospheric steam engine in 1705 to drive the independent water pump, which is called the newcomen atmospheric steam engine.