The function of heat engines is to convert heat energy into useful mechanical work. The working fluid in such installations is gas. It presses with effort on the turbine blades or on the piston, setting them in motion. The simplest examples of heat engines are steam engines and carburetor and diesel internal combustion engines.
Reciprocating heat engines have one or more cylinders with a piston inside. The expansion of the hot gas takes place in the volume of the cylinder. In this case, the piston moves under the influence of gas and performs mechanical work. Such a heat engine converts the reciprocating motion of the piston system into rotation of the shaft. For this purpose, the engine is equipped with a crank mechanism.
External combustion heat engines include steam engines, in which the working fluid is heated at the time of fuel combustion outside the engine. Heated gas or steam under high pressure and high temperature is fed into the cylinder. In this case, the piston moves, and the gas is gradually cooled, after which the pressure in the system becomes almost equal to atmospheric.
The spent gas is removed from the cylinder, into which the next portion is immediately fed. To return the piston to its initial position, flywheels are used, which are attached to the crank shaft. These heat engines can be single or double acting. In engines with a double action, there are two stages of the working stroke of the piston per shaft revolution; in installations with a single action, the piston makes one stroke in the same time.
The difference between internal combustion engines and the systems described above is that hot gas is obtained here by burning the fuel-air mixture directly in the cylinder, and not outside it. The supply of the next portion of fuel and the removal of exhaust gases is carried out through a system of valves. They allow you to supply fuel in a strictly limited amount and at the right time.
The source of heat in internal combustion engines is the chemical energy of the fuel mixture. This type of heat engine does not require an external boiler or heater. A variety of flammable substances act as a working fluid here, of which the most common are gasoline or diesel fuel. The disadvantages of internal combustion engines include their high sensitivity to the quality of the fuel mixture.
Internal combustion engines can be two- and four-stroke in design. Devices of the first type are simpler in design and not so massive, but with the same power, they require significantly more fuel than four-stroke ones. Engines that operate on two strokes are most often used in small motorcycles or lawn mowers. More serious machines are equipped with four-stroke heat engines.