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Figure 1: Heat engine diagram
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A heat engine is a system that converts heat to usable energy, particularly mechanical energy, which can then be used to do mechanical work.[1][2] While originally conceived in the context of mechanical energy, the concept of the heat engine has been applied to various other kinds of energy, particularly electrical, since at least the late 19th century.[3][4] The heat engine does this by bringing a working substance from a higher state temperature to a lower state temperature. A heat source generates thermal energy that brings the working substance to the higher temperature state. The working substance generates work in the working body of the engine while transferring heat to the colder sink until it reaches a lower temperature state. During this process some of the thermal energy is converted into work by exploiting the properties of the working substance. The working substance can be any system with a non-zero heat capacity, but it usually is a gas or liquid. During this process, some heat is normally lost to the surroundings and is not converted to work. Also, some energy is unusable because of friction and drag.
In general, an engine is any machine that converts energy to mechanical work. Heat engines distinguish themselves from other types of engines by the fact that their efficiency is fundamentally limited by Carnot's theorem of thermodynamics.[5] Although this efficiency limitation can be a drawback, an advantage of heat engines is that most forms of energy can be easily converted to heat by processes like exothermic reactions (such as combustion), nuclear fission, absorption of light or energetic particles, friction, dissipation and resistance. Since the heat source that supplies thermal energy to the engine can thus be powered by virtually any kind of energy, heat engines cover a wide range of applications.
Heat engines are often confused with the cycles they attempt to implement. Typically, the term "engine" is used for a physical device and "cycle" for the models.
^Fundamentals of Classical Thermodynamics, 3rd ed. p. 159, (1985) by G. J. Van Wylen and R. E. Sonntag: "A heat engine may be defined as a device that operates in thermodynamic cycle and does a certain amount of net positive work as a result of heat transfer from a high-temperature body to a low-temperature body. Often the term heat engine is used in a broader sense to include all devices that produce work, either through heat transfer or combustion, even though the device does not operate in a thermodynamic cycle. The internal-combustion engine and the gas turbine are examples of such devices, and calling these heat engines is an acceptable use of the term."
^Mechanical efficiency of heat engines, p. 1 (2007) by James R. Senf: "Heat engines are made to provide mechanical energy from thermal energy."
^Kenelly, A.E. (December 1898). "Discussion of 'Thermo-electric and galvanic actions compared'". Journal of the Franklin Society. CXLVI: 442.
^Laurie, Arthur Pillans (17 January 1914). "Faraday society". The Electrical Review. 72 (1834): 90. Retrieved 11 February 2023.
^Thermal physics: entropy and free energies, by Joon Chang Lee (2002), Appendix A, p. 183: "A heat engine absorbs energy from a heat source and then converts it into work for us.... When the engine absorbs heat energy, the absorbed heat energy comes with entropy." (heat energy ), "When the engine performs work, on the other hand, no entropy leaves the engine. This is problematic. We would like the engine to repeat the process again and again to provide us with a steady work source. ... to do so, the working substance inside the engine must return to its initial thermodynamic condition after a cycle, which requires to remove the remaining entropy. The engine can do this only in one way. It must let part of the absorbed heat energy leave without converting it into work. Therefore the engine cannot convert all of the input energy into work!"
A heatengine is a system that converts heat to usable energy, particularly mechanical energy, which can then be used to do mechanical work. While originally...
A Stirling engine is a heatengine that is operated by the cyclic compression and expansion of air or other gas (the working fluid) between different...
and mixing. Mechanical heatengines convert heat into work via various thermodynamic processes. The internal combustion engine is perhaps the most common...
A reciprocating engine, also often known as a piston engine, is typically a heatengine that uses one or more reciprocating pistons to convert high temperature...
Thermoacoustic engines (sometimes called "TA engines") are thermoacoustic devices which use high-amplitude sound waves to pump heat from one place to another...
A steam engine is a heatengine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure...
This timeline of heatengine technology describes how heatengines have been known since antiquity but have been made into increasingly useful devices...
Carnot, who in 1824 showed that the efficiency of conversion of heat to work in a heatengine has an upper limit. The first rigorous definition of the second...
In thermodynamics, heat is the thermal energy transferred between systems due to a temperature difference. In colloquial use, heat sometimes refers to...
upper limit on the efficiency of any classical thermodynamic engine during the conversion of heat into work, or conversely, the efficiency of a refrigeration...
Stirling engine range from mechanical propulsion to heating and cooling to electrical generation systems. A Stirling engine is a heatengine operating...
such as an internal combustion engine, steam turbine, steam engine, boiler, furnace, refrigerator, ACs etc. For a heatengine, thermal efficiency is the ratio...
An external combustion engine (EC engine) is a reciprocating heatengine where a working fluid, contained internally, is heated by combustion in an external...
vehicle's fuel efficiency. The efficiency of an engine is defined as ratio of the useful work done to the heat provided. η = w o r k d o n e h e a t a...
An internal combustion engine (ICE or IC engine) is a heatengine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion...
efficiency of heatengines, p. 1 (2007) by James R. Senf: "Heatengines are made to provide mechanical energy from thermal energy." "Understanding Heat Exchangers...
nitrogen engine is powered by liquid nitrogen, which is stored in a tank. Traditional nitrogen engine designs work by heating the liquid nitrogen in a heat exchanger...
a discourse on heat, power, energy and engine efficiency. The book outlined the basic energetic relations between the Carnot engine, the Carnot cycle...
reservoir temperatures and the heat absorbed to the engine QH (heatengine work output = heatengine efficiency × heat to the engine, where the efficiency is...
The Cyclone Waste HeatEngine (WHE) is a small steam engine developed to produce power from steam created from waste heat. It is an offshoot of the development...
A hot air engine (historically called an air engine or caloric engine) is any heatengine that uses the expansion and contraction of air under the influence...
drinky birds, water birds, dipping birds, and “Sippy Chickens” are toy heatengines that mimic the motions of a bird drinking from a water source. They are...
Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to an object to produce a unit change...
combustion engine cooling uses either air or liquid to remove the waste heat from an internal combustion engine. For small or special purpose engines, cooling...
The classic example of a heat exchanger is found in an internal combustion engine in which a circulating fluid known as engine coolant flows through radiator...
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