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Heat Engine

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What is a Heat Engine and its Types?

A heat engine is a device that turns heat into mechanical energy that can then be utilized to do work. It accomplishes this by lowering the temperature of a working substance from a higher state temperature. A heat source produces thermal energy, which raises the temperature of the working substance. The working material produces work in the engine's working body while transferring heat to a colder sink until it reaches a low-temperature state. 

Using the qualities of the working substance, some of the thermal energy is turned into work throughout this process. Any system with a non-zero heat capacity can be used as the working substance, however, it is most commonly a gas or liquid. Some heat is generally lost to the environment during this process and is not converted to work. Friction and drag also render some energy ineffective.

Types of Heat Engine

Heat engines have been classified according to the concept that governs their operation. Despite the fact that all of the ideas come from Thermodynamics, each type of heat engine converts heat energy into mechanical work using a different principle. The following are examples of different types of heat engines found in thermodynamics:

  1. Internal Combustion Engine- An internal combustion engine (ICE or IC engine) is a heat engine in which fuel is burned in a combustion chamber that is part of the working fluid flow circuit with an oxidizer (typically air). The expansion of the high-temperature and high-pressure gases produced by combustion acts directly on a component of an internal combustion engine. Pistons, turbine blades, a rotor, or a nozzle are usually the targets of the force. This force propels, moves, or powers whatever the engine is attached to by converting chemical energy into usable kinetic energy. For applications where engine weight or size are crucial, this has replaced the external combustion engine.

  2. Stirling Engine- A Stirling engine is a heat engine that works by compressing and expanding air or another gas (the working fluid) at different temperatures in a cyclic pattern, converting heat energy to mechanical work. The Stirling engine, in particular, is a closed-cycle regenerative heat engine with a constant gaseous working fluid.

Parts of a Heat Engine-

There are 3 important parts of a heat engine, and they are:

  1. Source- There must be an infinite thermal capacity source of heat that is kept at a constant high temperature so that whatever amount of heat is taken or added to it has no effect on its temperature.

  2. Working Substance- It has to be some kind of substance that absorbs or rejects heat into the sink. This is the active ingredient.

  3. Sink- There must be a finite thermal capacity sink, and it must be kept at a constant high temperature so that no quantity of heat is extracted or provided to it, and the temperature does not change.

What is an Ideal Heat Engine?

It's impossible to build a heat engine that's sole purpose is to absorb heat from a high-temperature environment and convert it all to work.

That is, there is no way to construct a heat engine that does not emit heat into the atmosphere.

Alternatively, it is impossible to create a heat engine with a 1.00 or 100% efficiency.


This is all about a heat engine, its different types, and how an ideal engine can be defined. Learn how an engine works and grab hold of the concept well. 

Last updated date: 27th May 2023
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FAQs on Heat Engine

1. Heat engines operate on what principle?

A heat engine is a machine that turns heat into mechanical energy. It extracts heat from a reservoir, does work such as moving a piston or lifting a weight, and then discharges some of the heat energy into a sink. There is just one operating ingredient in each engine. A vapour, for example, is a working substance in a vapour engine, much as fuel is in a petrol engine. The working substance absorbs heat from a high-temperature source, with a portion of that heat being converted into work and the remainder being stored in a low-temperature heat sink. The heat engine works on this basis.

2. Explain real-life examples of heat engines.

Thermal power plants, internal combustion engines, weapons, freezers, and heat pumps are all examples of heat engines. Heat engines that run in a forward motion, in which heat flows from a hot reservoir to a cool reservoir to create work as the desired product, are examples of heat engines.

3. Is it possible to cool a room by opening the door of the fridge?

No way. When a refrigerator operates in a confined room with the door shut, it rejects heat from the inside to the air in the space. As a result, the room's temperature gradually rises.

When the refrigerator door is left open, the heat rejected by the refrigerator to the room will be greater than the heat taken by the refrigerator, and the temperature of the room will rise at a slower rate than in the first instance.

As a result, keeping the door of an electric refrigerator open will not cool a room.

4. What are the Advantages of Heat Engines?

We have several benefits of using the heat engine. Some of them are:

  • It helps mankind to invent various machines.

  • It helps to regulate temperatures.

  • The cycling procedures are more advantageous than normal procedures.

  • As the fluids are allowed to high temperatures, we can yield high efficiency.

  • It consumes very little time and costs less.

  • The procedure and apparatus are also easy to use and simple to fix.

5. What do you mean by Heat Engine Cycle?

The heat engine is a system that helps to get useful work with the conversion of heat energy. Heat engine cycle is defined as the process of increasing in temperature and immersing the same in a cold reservoir to cool it down without any interruption. These reversible processes are known as a cycle.

6. What is the Secondary Classification of Heat Engines?

Along with two basic types of heat engines, we have another classification which consists of three types. They are:

Steam Engine: It uses coal for the conversion process. It transforms water into steam by the combustion process.

Reciprocating Steam Engine: We can understand from its name itself that it converts steam into the water by cooling effect.

Diesel Engine: It is widely used in heavy motors and vehicles. It helps to convert diesel into moving energy with air by heating it at high pressure.

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