An indicator diagram is a chart used to measure the thermal, or cylinder, performance of reciprocating steam and

internal combustion engines An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal comb ...

and compressors. An indicator chart records the

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...

in the cylinder versus the volume swept by the piston, throughout the two or four strokes of the piston which constitute the engine, or compressor, cycle. The indicator diagram is used to calculate the

work Work may refer to: * Work (human activity), intentional activity people perform to support themselves, others, or the community ** Manual labour, physical work done by humans ** House work, housework, or homemaking ** Working animal, an ani ...

done and the power produced in an engine cylinder or used in a compressor cylinder. The indicator diagram was developed by

James Watt James Watt (; 30 January 1736 (19 January 1736 OS) – 25 August 1819) was a Scottish inventor, mechanical engineer, and chemist who improved on Thomas Newcomen's 1712 Newcomen steam engine with his Watt steam engine in 1776, which was f ...

and his employee John Southern to help understand how to improve the

efficiency Efficiency is the often measurable ability to avoid making mistakes or wasting materials, energy, efforts, money, and time while performing a task. In a more general sense, it is the ability to do things well, successfully, and without waste. ...

steam engine A steam engine is a heat engine that performs Work (physics), mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a Cylinder (locomotive), cyl ...

s. In 1796, Southern developed the simple, but critical, technique to generate the diagram by fixing a board so as to move with the piston, thereby tracing the "volume" axis, while a

pencil A pencil () is a writing or drawing implement with a solid pigment core in a protective casing that reduces the risk of core breakage and keeps it from marking the user's hand. Pencils create marks by physical abrasion, leaving a trail of ...

, attached to a

pressure gauge Pressure measurement is the measurement of an applied force by a fluid (liquid or gas) on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of press ...

, moved at right angles to the piston, tracing "pressure". The indicator diagram constitutes one of the earliest examples of

statistical graphics Statistical graphics, also known as statistical graphical techniques, are graphics used in the field of statistics for data visualization. Overview Whereas statistics and data analysis procedures generally yield their output in numeric or tabul ...

. It may be significant that Watt and Southern developed the indicator diagram at roughly the same time that

William Playfair William Playfair (22 September 1759 – 11 February 1823) was a Scottish engineer and political economist. The founder of graphical methods of statistics, Playfair invented several types of diagrams: in 1786 he introduced the line, area and ...

(a former Boulton & Watt employee who continued an amicable correspondence with Watt) published ''The Commercial and Political Atlas,'' a book often cited as the first to employ statistical graphics. The gauge enabled Watt to calculate the work done by the steam while ensuring that its pressure had dropped to zero by the end of the stroke, thereby ensuring that all useful

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

had been extracted. The total work could be calculated from the area between the "volume" axis and the traced line. The latter fact had been realised by Davies Gilbert as early as 1792 and used by Jonathan Hornblower in

litigation A lawsuit is a proceeding by one or more parties (the plaintiff or claimant) against one or more parties (the defendant) in a civil court of law. The archaic term "suit in law" is found in only a small number of laws still in effect today. ...

against Watt over

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an sufficiency of disclosure, enabling discl ...

s on various designs.

Daniel Bernoulli Daniel Bernoulli ( ; ; – 27 March 1782) was a Swiss people, Swiss-France, French mathematician and physicist and was one of the many prominent mathematicians in the Bernoulli family from Basel. He is particularly remembered for his applicati ...

had also had the insight about how to calculate work. Watt used the diagram to make radical improvements to steam engine performance and long kept it a trade secret. Though it was made public in a letter to the '' Quarterly Journal of Science'' in 1822, it remained somewhat obscure, John Farey, Jr. only learned of it on seeing it used, probably by Watt's men, when he visited Russia in 1826. In 1834, Émile Clapeyron used a diagram of pressure against volume to illustrate and elucidate the

Carnot cycle A Carnot cycle is an ideal thermodynamic cycle proposed by French physicist Nicolas Léonard Sadi Carnot, Sadi Carnot in 1824 and expanded upon by others in the 1830s and 1840s. By Carnot's theorem (thermodynamics), Carnot's theorem, it provides ...

, elevating it to a central position in the study of

thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed b ...

. Later instruments for steam engine (''illus.'') used paper wrapped around a cylindrical barrel with a pressure piston inside it, the rotation of the barrel coupled to the piston crosshead by a weight- or spring-tensioned wire. In 1869 the British marine engineer Nicholas Procter Burgh wrote a full book on the indicator diagram explaining the device step by step. He had noticed that "a very large proportion of the young members of the engineering profession look at an indicator diagram as a mysterious production." Indicators developed for steam engines were improved for internal combustion engines with their rapid changes in pressure, resulting from combustion, and higher speeds. In addition to using indicator diagrams for calculating power they are used to understand the ignition, injection timing and combustion events which occur near dead-center, when the engine piston and indicator drum are hardly moving. Much better information during this part of the cycle is obtained by offsetting the indicator motion by 90 degrees to the engine crank, giving an offset indicator diagram. The events are recorded when the velocity of the drum is near its maximum and are shown against crank-angle instead of stroke.Internal Combustion Engines Theory and Design, Maleev, First edition 1933, McGraw-Hill Book company, Inc., p. 33.

References

Bibliography

* *Pacey, A.J. & Fisher, S.J. (1967) "Daniel Bernoulli and the ''vis viva'' of compressed air", ''The British Journal for the History of Science'' 3 (4), pp. 388–392, *British Transport Commission (1957) ''Handbook for Railway Steam Locomotive Enginemen'', London : B.T.C., p. 81, (facsimile copy publ. Ian Allan (1977), )

External links

* {{Commons category, Indicator diagrams, position=left Energy conversion Piston engines Steam power Thermodynamics Diagrams

See also

References

Bibliography

External links