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steam cylinder atmospheric pressure

An engine is a mechanical contrivance by means of which some form of energy is converted to useful work. The first mechanical utilization of an energy source to do work dates back to the 1st-c BC , when simple water wheels were used to lift water from rivers and to mill grain. Although it might be considered that these were examples of simple hydraulic ‘engines’, it is generally accepted that the term engine is associated with a much later period of technological development; that of the Industrial Revolution. Engines are normally associated with the conversion of fossil fuels (thermal energy sources) into useful work, and so we may fully refer to them as heat engines.

The most significant heat-engine development was that of the steam engine. The use of steam to produce a mechanical effect has its origin in the 1st-c AD , when the mathematician and inventor of Alexandria described a steam-operated ‘wheel’ which utilized the thrust effect of escaping steam jets. This device was really only a toy, and no attempt was made to find a use for it. Hero demonstrated other interesting arrangements and, although none of them led to the development of a practical heat engine, he did go some way to demonstrate that when a fluid such as water or air is heated, it is possible to use it to bring about some form of mechanical effect.

In 1661, , in Magdeburg, invented a device consisting of a close-fitting piston within a pipe with a closed end. Using a vacuum pump (which he had also developed), he created a partial vacuum inside the pipe, the pressure there falling below that of the atmosphere. Atmospheric pressure acting on the other side of the piston then forced it into the pipe. The piston was connected by a system of ropes and pulleys to a weight which was then raised. This was the forerunner of the various heat engines which were generally categorized as atmospheric engines, since they all made use of the fact that atmospheric pressure, in conjunction with a partial vacuum created within a piston–cylinder arrangement, could do useful work.

It was the Frenchman Denis Papin (1647–1712) who first had the idea of constructing an atmospheric engine which made use of the evaporation and condensation properties of water. In 1689 he demonstrated what was in effect an embryo steam engine. It consisted of a vertical hollow cylinder with a base, above which was a piston. A small amount of water within the piston-cylinder arrangement was heated; steam was generated and it was allowed to expand, thereby pushing the piston up the cylinder. It was then held by a catch while the steam cooled and condensed, with a consequent reduction in its pressure. When the catch was released, atmospheric pressure acting on the top of the piston forced it back to the bottom of the cylinder. Although Papin’s arrangement had limited application, it was a significant step towards the goal of obtaining a practical steam engine.

In 1698 Thomas Savery ( c .1650–1715), an English engineer, patented a steam pump which could be used to pump water out of mines. His machine was a simple arrangement with no piston and requiring the hand operation of valves. It used steam above atmospheric pressure. Since it did not have automatic safety valves, and as reliable boilers had not been perfected, the Savery pump proved to be dangerous and it was eventually abandoned. About the same period Thomas Newcomen (1663–1729) was also engaged in the design of a steam-operated pumping engine. Newcomen’s design was different from Savery’s, but as the latter’s patent was very general and protected the rights for the raising of water ‘by the impellent force of fire’, it was necessary for Newcomen to liaise with Savery in 1705 to come to some arrangement regarding the manufacture of his engine. In 1712 the first practical Newcomen steam engine was constructed. It was an atmospheric engine and was thus dependent for its operation on obtaining a pressure within the cylinder below that of atmospheric pressure; this was achieved by injecting cold water into steam in the cylinder. This engine proved to be a significant breakthrough in atmospheric engine development, and Newcomen-type engines were manufactured and sold in numbers for mine pumping.

While preparing a model of a Newcomen engine for Glasgow University in the winter of 1763–64, , a Scottish instrument-maker, realized that a considerable amount of heat was wasted by successively heating the cylinder to produce steam and subsequently cooling it to condense the steam. He proposed a major improvement to Newcomen’s design, by the use of a cooling chamber (a condenser) separate from the steam cylinder. His design also incorporated an air pump which, by sucking air out of the condenser, created a partial vacuum which assisted condensation of the steam. This allowed a large increase in the overall efficiency of the engine. Watt obtained a patent for his engine in 1769. In order to exploit his invention commercially, he joined forces with the leading Birmingham manufacturer, Matthew Boulton (1728–1809). This was a very significant industrial partnership, and the widespread use of Watt’s engine began in 1776–77. Watt’s engine was much lower in coal consumption than Newcomen’s, which was an attractive selling point. Page 279  In 1782, Watt patented a double-acting engine in which steam was used alternately below and above the piston to produce a power stroke in both directions, thereby making it more suitable for the eventual use of a rotative motion, required to operate factory machinery. Both the Newcomen and Watt engines transmitted work through massive beams.

Further developments in steam engine design did not take place until the early 1800s, when steam above atmospheric pressure was investigated. The Cornish engineer Richard Trevithick (1771–1833) realized that the need to create a vacuum within the cylinder, requiring a cumbersome and heavy condenser, could be replaced by making use of high-pressure steam. This was a departure from the atmospheric type of engine. He perfected the first high-pressure steam engine in about 1803. In the same year he also built the first steam locomotive at the Coalbrookdale ironworks, thereby giving a further boost to the Industrial Revolution. From the 1830s steam locomotives dominated rail transport for over a century.

In parallel with the early development of the steam engine, several inventors pursued the idea of an engine in which the combustion of a fuel would take place within a piston-cylinder arrangement. In 1673 the Dutch scientist demonstrated a piston engine to the French Académie des Sciences. It was an atmospheric-type engine which made use of a small quantity of explosive. It worked by displacing cold air from the cylinder by means of the hot gases from the explosion. When the hot gases remaining in the cylinder cooled and contracted, the cylinder gas pressure was lower than the atmospheric pressure outside the arrangement and, like other atmospheric-type engines, movement of the piston was effected. This invention was unfortunately thwarted by the inability to find a suitable fuel. It was much later that it was found that when coal is heated in a closed vessel a combustible gas (coal gas) is given off, which forms a suitable fuel.

In 1816, Robert Stirling (1790–1878), a Scottish clergyman, developed another concept; that of an engine with air as the operating medium. His engine consisted of two cylinders. In one of them air was heated (by an external source) and cooled alternately. When the air expanded, it effected a power, or working, stroke in the other cylinder. This engine was a closed-circuit, hot-air type, and its operating principle was later seen to be based on excellent thermodynamic considerations. Stirling obtained a patent for his design in 1827. Some engines were manufactured industrially in 1844, but they never attained mass production. Later, Stirling engines used helium and hydrogen. (Even up to the present time, these engines, owing to their stringent manufacturing requirements, are confined to special applications, such as submarines and spacecraft.)

In 1824 published his work which, in discussing steam engine efficiency, created the new science of thermodynamics. The next 30 years saw several designs and patents for gas engines, but most of them were never constructed; those that were had limited success. The first internal combustion engine able to operate reliably was built by the Belgian-born inventor Jean Joseph Lenoir (1822–1900). In 1860, he patented a well-thought-out design for a gas engine. The fuel was lighting gas (derived from coal) mixed with air. This engine was a two-stroke, double-acting design, with the fuel-air mixture fed into the cylinder alternately at either end of the piston. The Lenoir engine was slow-running (200 rpm), and the gas-air mixture was not compressed before ignition. It lacked power, and it had a very high fuel consumption. Despite this, it sold in reasonable numbers, and so became the first internal combustion engine to compete with the long-established dominance of steam. In 1862, the French engineer Alphonse Beau de Rochas (1815–93) described the much more efficient four-stroke cycle. However, his proposed engine was never constructed, and he allowed his patent to lapse. It was the German engineer who constructed the first four-stroke internal combustion engine in 1876. This design was a significant one from the viewpoint of the development of the motor car. These early internal combustion engines all operated on gas. The use of liquid fuels was not introduced until near the end of the 19th-c. In 1883, the German engineers Gottlieb Daimler (1834–1900) and Wilhelm Maybach (1846–1929) designed an engine that could operate on petrol. It ran faster than Otto’s engine and was capable of obtaining more power for a given weight of engine. In 1889 the engine was installed in a car designed by Maybach, which is considered to be the first modern motor car. The heavy-oil engine was pioneered in Britain in 1890 by Herbert Akroyd-Stuart and improved by the German engineer . In 1893, Diesel patented a prototype four-stroke engine. This engine differed from the petrol engine in that ignition of the fuel occurred spontaneously without a spark. The high compression attained within the cylinder resulted in sufficiently high temperatures to bring about ignition of the fuel and effect a pressure stroke. The Diesel engine has of course found wide use for both marine and land transport.

Another, more recent development in internal combustion engine design was the rotary engine, invented in 1956 by the German engineer . In this engine the conventional reciprocating action of pistons in cylinders is replaced by the rotary motion of an ingeniously designed rotor within a specially shaped chamber. This design has not found widespread application within the automobile industry, in which conventional petrol engines and Diesel engines seem destined to continue their dominance.

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