Compound steam engine

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Steam engine unit vapor compound is a steam engine type where the vapor is expanded in two or more stages. The general arrangement for compound machines is that the vapor is first expanded in the high pressure of the cylindrical (i) (HP) cylinder, then after releasing the heat and the pressure loss, it flows directly to one or more low pressure volumes (LP ) cylinder. The multi-expansion machine uses an additional cylinder, the lower the pressure, to extract further energy from the steam.

Created in 1781, this technique was first used on a Cornish beam machine in 1804. Around 1850, compound machines were first introduced to the Lancashire textile mills.

Video Compound steam engine

Sistem compound

There are many compound systems and configurations, but there are two basic types, according to how the HP stroke and LP piston are gradual and hence whether the HP exhaust can pass directly from HP to LP (Woolf compound) or whether pressure fluctuations require a medium "buffer" the shape of a vapor or pipe known as the receiver (the receiving compound).

In a single-expansion (or 'simple') steam engine, high-pressure vapor enters the cylinder at the boiler pressure through the inlet valve. The vapor pressure forces the piston down into the cylinder, until the valve closes (eg After 25% of the piston stroke). Once the steam supply is disconnected, the steam trapped continues to expand, pushing the piston to the end of its sweep, where the exhaust valve opens and releases the partially drained vapor into the atmosphere, or into the condenser. This "cut-off" allows more work to be extracted, since the expansion of steam is doing additional work beyond that done by steam at boiler pressure.

Cut-offs previously increased the expansion ratio, which in principle allows more energy to be extracted and increases efficiency, but when the trapped vapor expands, the temperature drops. This temperature drop will occur even if the cylinder is completely isolated so that no heat is released from the system (see adiabatic and heating process § adiabatic and cooling). As a result, the steam enters the cylinder at high temperatures and leaves at a lower temperature. The alternating steam temperature alternately heats and cools the cylinder with each stroke and is an inefficient source of inefficiency at higher expansion ratios. Beyond a certain point, increasing the expansion ratio will actually decrease efficiency due to increased heating and cooling.

Compounding machine

A method to reduce the size of heating and cooling was discovered in 1804 by the British engineer Arthur Woolf, who patented the Woolf high pressure compound engine in 1805. In a compound machine, high-pressure steam from the first boiler expands in a cylinder high pressure (HP) and then enter one or more next low pressure cylinder (LP). The complete expansion of steam occurs in some cylinders and, because there is little expansion in each cylinder, less heat is lost by steam in each cylinder. This reduces the amount of heating and cooling of the cylinder, creating a higher practical expansion ratio and improving engine efficiency.

There are other advantages: because the temperature range is smaller, the cylinder condensation is reduced. Losses due to condensation are limited to LP cylinders. The pressure difference is less in each cylinder so there is less steam leakage on the piston and the valve. The turning moments are more uniform, so balancing is easier and smaller flywheels can be used. Only smaller HP cylinders need to be built to withstand the highest pressure, which reduces overall weight. Similarly, components are subject to less stress, so they can be lighter. The reciprocating engine parts are lighter, reducing engine vibration. The compound can be started at any point in the cycle, and in the case of mechanical failure, the compound can be rearranged to act as simple, and thus keep it running.

To obtain the same job from lower pressure steam, a larger cylinder volume is required as this steam occupies a larger volume. Therefore, holes, and often strokes, increase on low pressure cylinders, resulting in larger cylinders.

Double expansion (usually known simply as 'combined') extends the vapor in two stages, but this does not mean that all the machines have two cylinders. They may have four cylinders that function as two LP-HP pairs, or large LP cylinder jobs can be divided into two smaller cylinders, with one HP cylinder exhausted into the LP cylinder, providing a 3-cylinder layout in which the cylinder and piston diameter all three are about the same, making reciprocating masses easier to balance.

The two-cylinder compound can be arranged as:

• Cross-compound - cylinder side by side
• Tandem compound - end to end cylinder, drive common connecting rod
• Telescopic compound - cylinder is one inside the other
• Angle-compound - the cylinder is arranged in a vee (usually at an angle of 90 °) and pushes the general crank.

The adoption of compounding is widespread for stationary industrial units where the need for increased power at a reduced cost, and almost universal for marine engines after 1880. It is not widely used in railroad locomotives where it is often perceived as intricate and unsuitable for rough. the operating environment of trains and limited space provided by gauges (especially in the UK). Compounding was never common in British railways and was not used at all after 1930, but was used limitedly in many other countries.

The first successful attempt to fly a fixed wing aircraft heavier than air only in steam power took place in 1933, when George and William Besler transformed Air Air 2000 aircraft into flight with a 150-liter V-twin engine steam from their own design not the usual Curtiss OX-5 inline engine or a commonly used radial aviation gasoline engine.

Multi-expansion machine

This is the logical extension of the compound machine (described above) to divide the expansion into more stages to improve efficiency. The result is a multi-expansion engine . The machine uses three or four expansion stages and is known as triple - and quadruple-expansion engine sequentially. This machine uses a series of double working cylinders that progressively increase the diameter and/or stroke and hence volume. This cylinder is designed to divide the work into three or four equal parts, one for each stage of expansion. The image on the right shows a triple-expansion machine animation. Steam flows through the engine from left to right. The valve crates for each cylinder are to the left of the corresponding cylinder.

Maps Compound steam engine

History

Initial work

• 1781 - Jonathan Hornblower, grandson of one of Newcomen's engine erectors in Cornwall, patented a two-cylinder reciprocating cylinder engine in 1781. He was prevented from further expansion by James Watt, who claimed his own patent. has been violated.
• 1804 - A method to reduce the magnitude of the continuous heating and cooling of a single expansion steam engine leading to inefficiency was discovered by British engineer Arthur Woolf. Woolf patented his stationary Woolf high-pressure compound engine in 1805.

Double expansion

• 1845 - William McNaught devised a method for fixing an additional high-pressure cylinder in the existing jet engine. To do so involved using a long pipe to connect the cylinder, and a set of extra valves to balance it. Consequently this acts as a receiving chest, and new types of compounds have been found. This system allows for greater control of steam and cut-off intake. The engine can be slowed down by a throttle that reduces the vapor pressure, or by adjusting the cut-off on both cylinders. The latter is more efficient because no power is lost. The cycle is more fluent because the two cylinders are not in phase.
• 1865 - SSÃ, Agamemnon Ã, (1865) was launched, equipped with a 300hp compound steam engine. The machine was designed by Alfred Holt, one of the owners. The efficiency obtained allows this ship to travel 8,500 miles before coaling. This makes it competitive on routes between China and the UK.
• Understand thermodynamics rather than believe in calories
• Corliss Valves

Double expansion

• 1861 - Daniel Adamson takes the patent for a multi-expansion machine, with three or more cylinders connected to one beam or crankshaft. He built a triple-expansion engine for Victoria Mills, Dukinfield which opened in 1867.
• 1871 - Charles Normand, from Le Havre installed a triple-expansion machine to the Seine river ship in 1871.
• 1872 - Sir Fredrick J. Bramwell reports that a combined marine engine, operating at 45psi to 60psi, spends 2 lbs to 2.5 lbs per indicated horsepower.
• 1881 - Alexander Carnegie Kirk builds SS Aberdeen , the first major vessel powered by a threefold expansion engine.
• 1887 - HMS Victoria was launched, the first battleship powered by three expansion machines.

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Apps

Pumping machine

Mill Machine

Although the first plant is powered by hydro power, once the steam engine is adopted, the manufacturer is no longer required to place the plant by running water. Cotton spinning requires a larger plant to meet demand, and this encourages owners to demand an increasingly powerful machine. When the boiler pressure has exceeded 60psi, the compound engine achieves a thermo-dynamic gain, but it is the mechanical advantage of the smoother stroke that is the deciding factor in the adoption of the compound. In 1859, there were 75,886 ihp (indicated horsepower) from a machine at a factory in the Manchester area, where 32,282 ihp was provided by the compound even though only 41,189 ihp was produced from the boiler operated at over 60psi.

To generalize, between 1860 and 1926 all Lancashire factories were driven by compounds. The last compound that was built was by Buckley and Taylor for the Wye No.2 factory, Shaw. This machine is a cross-compound design for 2,500 ihp, riding a flywheel 24Ã, ft, 90 tons, and operated until 1965.

Ocean applications

In marine environments, the general requirement is for autonomy and increased range of operations, since ships must carry their coal supply. Therefore, old brine boilers are no longer adequate and should be replaced with enclosed freshwater circuits with condensers. The results from 1880 onwards are multi-expansion machines using three or four expansion stages ( triple - and quadruple expansion engines ). These machines use a series of double-acting cylinders that progressively increase the diameter and/or stroke (and hence volume) designed to divide the work into three or four appropriate parts for each stage of expansion. Where space is at a premium, two smaller cylinders of large volumes may be used for low pressure stages. Multi-expansion machines usually have cylinders arranged in-line, but various other formations are used. At the end of the 19th century, the Yarrow-Schlick-Tweedy balance system was used on some marine triple-expansion machines. The Y-S-T engine divides the low-pressure expansion stage between two cylinders, one on each end of the machine. This allows the crankshaft to become more balanced, resulting in a smoother and faster response engine that runs with less vibration. This makes the three-cylinder three-cylinder expansion engine popular with large passenger liners (like the Olympic class), but ultimately replaced by a vibration-free steam turbine.

The development of this type of machine is important for its use in steamers because by straining it into a water condenser it can be reclaimed to feed the boiler, which can not use seawater. Ground-based steam engines can only drain a lot of their steam, as feed water is usually available. Prior to and during World War II, expansion machines dominated sea applications where high vessel speeds were not important. It was replaced by a steam turbine when speed was needed, as for warships and ships. HMS Dreadnought in 1905 was the first major battleship to replace proven technology from reciprocating engines with new-steam turbines.

Apps to rail locomotive

For rail locomotive applications, the main benefit sought from incorporation is the economy in fuel and water consumption plus a high power/weight ratio due to temperature and pressure drops that occur during longer cycles, resulting in increased efficiency; Additional perceived benefits include more torque.

While the design for the combined locomotive may date as far as James Samuel's 1856 patent for "continuous expansion locomotive", the practical history of compounding railways began with the Anatole Mallet design in the 1870s. Locomotive Mallet is operated in the United States until the end of mainstream steam by Norfolk and Western Railway. The design of Alfred George de Glehn in France also sees significant use, especially in rebuilding AndrÃÆ' Â © Chapelon. Various compound designs were tried around the year 1900, but most were short-lived in popularity, due to their complexity and maintenance obligations. In the 20th century, superheater was widely adopted, and most steam locomotives were simple expansion (with some combined locomotives converted to simple).

Large American locomotives use 2 compressed air vapor compressors, for example Westinghouse 8 1/2 "150-D, for the train brakes.

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Note

^ Ã, Phasing cylinder: Ã, With a two-cylinder compound used in rail work, the piston is connected to the crank as with a simple two-cylinder at 90 ° off-of-phase with each other ( quartered ).

When the double-expansion group is doubled, producing a 4-cylinder compound, the individual piston in the group is usually balanced at 180 °, the groups being set at 90 ° to each other. In one case (the first type of Vauclain compound), the piston works in the same phase driving a common crosshead and crank, again set at 90 ° like for a two-cylinder engine.

With a 3-cylinder compound arrangement, the LP crank is set to 90 Â ° with the HP one at 135 Â ° to the other two, or in some cases the three cranks installed at 120 Â °.

^ Ã, ihp: Ã, The power of the factory machine was initially measured in Nominal Horse Power, but the system lacked the power of the system McNaught compounds suitable for the compound, ihp or indicated horsepower. As a rule of thumb ihp is 2.6 times nhp, in compound machines

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See also

• Turbine compound
• Willans Machine

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References

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Bibliography

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External links

• Northern Mill Engine Society at Bolton Steam Museum

Source of the article : Wikipedia