Heat engines

What are heat engines? Examples, types and definition

What are heat engines? Examples, types and definition

Heat engines are a type of reciprocating engine. They are actually the most popular reciprocating engines.

This type of engine uses the thermal energy caused by the combustion of a fuel (generally diesel or gasoline) to convert it into mechanical energy .

Examples of heat engines

Some examples of heat engines are the following:

  • The engine of a gasoline vehicle.

  • An electric generator.

  • A nuclear power plant: nuclear power plants obtain mechanical work from the heat generated in nuclear reactions.

  • The engine of a steam train.

Types of heat engines

A heat engine can be classified in many different ways. In one of these classifications it can be distinguished between:

  • Internal combustion engines: Combustion occurs in an internal chamber of the engine itself, where gases are generated that produce the expansion caused by work. For example, car engines.

  • External combustion engines: These are those in which combustion takes place outside the engine. The heat released is transmitted to an intermediate fluid. This intermediate flow produces mechanical energy. For example, the steam engine, where the intermediate fluid is steam and the place of combustion is the boiler, which is outside the engine. Another example would be the heat engines of nuclear power plants that use nuclear energy to convert it into mechanical energy.

Internal combustion engines

Within internal combustion engines, two types of engines stand out: the diesel engine and the gasoline engine.

The difference between one and the other differs especially by the way of initiating the ignition of the fuel. From here, the cycle between one and the other is very similar.

How does an internal combustion engine work?

The engine piston transmits the thrust of the gas generated during combustion, through the bolt, to the connecting rod. The thrust of the connecting rod is transmitted to the crank of the crankshaft or drive shaft. The connecting rod and the crank transform the reciprocating linear movement of the piston into a rotary movement of the crankshaft. The crankshaft rotates between main bearings, mounted on the bed itself.

Combustion gases are released to the outside through the exhaust valve and the exhaust manifold.

Both the suction valve and the exhaust valve are actuated by organs called distribution. The crankshaft drives the timing shaft by means of a chain or with gears. Axle-mounted trucks act on a number of parts, such as tappets, tappets, and rocker arms.

These parts transmit the movement to the valve that opens and closes during the rotation of the shaft due to the asymmetric shape of the corresponding camon.

When the trucks do not apply pressure to the valve, it is held in position by a spring.

What are the peculiarities of the diesel engine?

The diesel engine works by means of the diesel cycle. It is also called a compression ignition engine because the fuel is ignited by subjecting it to very high pressure.

The fuel inlet is via an injector. The injection pump regulates the amount of fuel that must enter at all times. On the other hand, there is no regulation for the amount of air that enters through the duct and the suction valve.

The diesel engine does not need a spark plug because combustion occurs by compressing the air in the cylinder, increasing the temperature enough to initiate ignition.

What are the peculiarities of the gasoline engine?

Gasoline engines operate on the Otto cycle. It is also called an Otto engine or a spark ignition engine.

An important feature of the Otto engine is the way the fuel is ignited. In this case, it is produced by a spark caused by a spark plug.

In the gasoline engine, the mixture is formed in the carburetor (nowadays no longer used and the mixture is carried out by means of injectors in the combustion chamber) and enters the cylinder through the duct and the suction valve .

The fuel butterfly valve is used to regulate the amount of mixture entering the cylinder.

Differences between a heat machine and a heat engine

The concept of a heat machine is often confused with that of a heat engine. These terms are related but are not exactly the same.

A heat machine is a device or system that works by establishing heat and work exchanges with its environment.

To achieve this, the machine transforms a substance through a cyclical process or a sequence of operations. At the end of each cycle the substance returns to its original state and a new cycle begins.

A heat engine can function as a motor, if it converts heat into work, or as a refrigerator or heat pump if it converts work into heat.

Publication Date: November 28, 2016
Last Revision: September 15, 2021