The concept of a thermal engine is often confused with that of a thermal engine. These terms are related but not exactly the same. A thermal machine is a device or system that works by establishing exchanges of heat and work with its environment. To achieve this, the machine transforms a substance through a cyclic process or a sequence of operations. At the end of each cycle the substance returns to its original state and a new cycle begins. It can work as an engine, if it turns heat into work, or as a refrigerator or heat pump if it turns work into heat.
Thermal machines transform mechanical energy into thermal energy, and vice versa. If you turn heat into work, it works as an engine. On the other hand, if it turns work into heat, it acts as a heat pump.
The most common examples of thermal machines that we find are the diesel thermal engines and the gasoline engines found in automobiles. Many HVAC systems use heat pumps that are also thermal machines.
Classification of heat engines
A thermal engine can be classified in many different ways. In one of these classifications you can distinguish between:
- Internal combustion engines: The combustion takes place in an internal chamber of the motor itself, where the gases that produce the expansion caused by the work are generated. For example, the engines of cars.
- External combustion engines: Those in which combustion takes place outside the engine. The heat released is transmitted to an inert medium. This intermediate flow produces mechanical energy. For example, the steam engine, where the intermediate fluid is water vapor and the place of combustion is the boiler, which is outside the engine. Another example would be the thermal engines of nuclear power plants that use nuclear energy to convert it into mechanical energy.
Internal combustion engine
Inside the internal combustion engines stand out two types of engines: the diesel engine and the gasoline engine.
The difference between one and the other is differentiated especially by the way to start the ignition of the fuel combustion. From here, the cycle between one and the other is very similar.
The piston or piston (equipped with compression rings that prevent the escape of gas between piston and cylinder) transmits the thrust of said gas generated during combustion, through the bolt, to the 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 rotary movement of the crankshaft. The crankshaft rotates between main bearings, mounted on the base itself.
the exhaust valve and the exhaust manifold are the conduits through which the products of combustion are discharged to the outside.
Both the suction valve and the exhaust valve are driven by so-called distribution organs. A distribution axle or axle of trucks is driven by the crankshaft by means of a chain or by gears. The trucks mounted on the shaft act on a series of parts, such as tappets, pushers and rockers. These parts transmit the movement to the valve according to the law defined by the shape of the corresponding truck. The valve is held in its seat by the action of its spring.
The diesel engine is an internal combustion thermal engine.
This type of engine is characterized to work through the diesel cycle. It is also called a compression ignition engine because the ignition of the fuel is produced by subjecting it to a very high pressure.
Fuel is introduced into the cylinder by means of an injector. The amount of fuel of a diesel engine is regulated by the injection pump. On the other hand, there is no regulation for the amount of air entering through the conduit and the suction valve.
Otto engines are a type of internal combustion engine. This type of motor works according to the Otto cycle, for this reason it is also called the Otto motor.
An important feature is the way the ignition of the fuel starts. In this case, it is produced by a spark caused by a spark plug. Due to this characteristic, it can also be referred to as a spark ignition engine.
In the gasoline engine, the mixture is formed in the carburetor (nowadays it is little used and the mixture is made by injectors in the combustion chamber) and enters the cylinder through the conduit and the valve. aspiration. The throttle valve of the fuel serves to regulate the amount of incoming mixture.
Last review: November 24, 2017