The reciprocating engine uses the reciprocating motion of one or more pistons to convert the pressure into a working fluid. Generally this work is in the form of rotational movement, that is, we obtain mechanical energy. In the reverse direction we find rotary machines in which the movement of the machine parts is already rotational, such as turbines or the Wankel motor.
What are the types of reciprocating engine?
Alternative engines can be classified in many different ways. The main forms of classification are the following:
- According to the arrangement of the cylinders in the engine
- According to the displacement
- According to the compression ratio
- According to the relation of diameter and stroke
- According to the number of movements of each cycle
Combustion engines are further classified in two ways:
- Spark ignition engines. It is also known as the gasoline engine, Otto engine, or explosion engine. In this case, the spark plug starts fuel combustion.
- The diesel engine. It is also known as a compression ignition engine. In the diesel engine the air inside the cylinder is compressed, when compressed it is heated allowing the fuel to ignite.
Despite the importance of endothermic motors, there are other types of alternative motors:
- The steam engine, the mainstay of the Industrial Revolution
- The Stirling engine.
What are the types of spark ignition engines?
The main types of spark ignition engines are as follows:
- Gasoline engine: It is the most common version since it is installed in an important part of automobiles. You have two fuel supply options: an injector and a carburetor.
- Carburetor engine. A feature is the production of a mixture of fuel and gas in a special mixer, carburetor. Previously, such gasoline engines prevailed; Now, with the development of microprocessors, its field of application is rapidly decreasing.
- Injection engine. A characteristic is the reception of the fuel mixture in the manifold or in the engine cylinders feeding the fuel injection system.
- Gas engines. An engine that burns gaseous hydrocarbons as fuel under normal conditions: mixtures of liquefied gases, compressed natural gases, gas obtained by converting solid fuel into gaseous. As solid fuel are used: coal, peat, wood.
These engines are widely used, for example, in small and medium power power plants , using natural gas as fuel (in the high power area, gas turbine power units reign).
What are the types of compression ignition engines?
The diesel engine is characterized by ignition of the fuel without the use of a spark plug. A portion of fuel is injected into the heated air in the cylinder from adiabatic compression (at a temperature that exceeds the ignition temperature of the fuel) through the nozzle.
During the injection of the fuel mixture, it is sprayed, and then around the individual droplets of the fuel mixture there are sites of combustion, as the fuel is injected, the fuel mixture burns in the form of a torch. Since diesel engines are not subject to detonation, the use of higher compression ratios is permitted.
Raising it more than 15 practically does not increase efficiency, since in this case the maximum pressure is limited by a longer combustion and a decrease in the injection advance angle. However, small-size high-speed vortex chamber diesel engines can have a compression ratio of up to 26, for reliable starting in conditions of high heat removal and for less stiffness (stiffness is caused by delay at ignition, characterized by an increase in pressure during combustion, measured in MPa / degree of rotation of the crankshaft).
Oversized marine supercharged diesel engines have a compression ratio of approximately 11..14 and an efficiency of more than 50%.
Diesel engines are usually less fast and with the same power as gasoline are characterized by high torque on the shaft. In addition, some large diesel engines are adapted to operate on heavy fuels, such as fuel oils .
Large diesel engines are launched, as a rule, by the pneumatic circuit with compressed air supply or, in the case of diesel generator sets , from a connected electric generator , which, when launched, acts as a motor boot .
Contrary to popular belief, modern engines, traditionally called diesel engines, do not operate according to the Diesel cycle , but rather according to the Trinkler - Sabate cycle with a mixed supply of heat. The disadvantages of diesel engines are due to the peculiarities of the work cycle: greater mechanical stress, which requires greater structural resistance and, as a consequence, an increase in its dimensions, weight and increased costs due to the complicated design and use of more expensive materials.
Furthermore, diesel engines due to heterogeneous combustion are characterized by unavoidable soot emissions and a higher content of nitrogen oxides in the exhaust gases.
The main portion of the fuel is prepared, as in one of the varieties of gas engines, but is not lit by an electric candle, but by a pilot portion of diesel fuel injected into the cylinder similar to a diesel engine.
Usually there is the possibility of working on a purely diesel cycle. Application: heavy trucks. Gas-diesel engines, like gas engines, produce less harmful emissions, in addition, natural gas is cheaper.
Such an engine is often obtained by retrofitting one in series, while diesel fuel economy (degree of gas substitution) is approximately 60% . Foreign companies are also actively developing such designs .
Alternative Engine History
A prime example of the well-known history of rotary to reciprocating motion is the crank mechanism. The oldest hand cranks appeared in China during the Han dynasty (202 BC-220 AD). Several sawmills in Roman Asia and Byzantine Syria during the 3rd-6th centuries AD had a connecting rod mechanism that converted the rotary motion of a water wheel into the linear motion of saw blades. In 1206, the Arab engineer Al-Jazari invented a crankshaft.
The reciprocating engine was developed in Europe during the 18th century, first as an atmospheric engine and later as the steam engine. These were followed by the Stirling engine and the internal combustion engine in the 19th century. Today, the most common form of reciprocating engine is the internal combustion engine that runs on the combustion of gasoline, diesel, liquefied petroleum gas (LPG), or compressed natural gas (CNG) and is used to power motor vehicles and motor plants.
Alternative engine terminology
Not all reciprocating motors correspond to the scheme described, but the essential parts and their operation are similar.
Below we attach a terminology universally used in the field of internal combustion engines or endothermic engines. This terminology is used to indicate some dimensions and fundamental values of this type of engine.
- Top dead center (PMS). Position of the piston closest to the cylinder head. Lower Dead Point (PMI). Position of the piston furthest from the cylinder head.
- Lower Dead Point (PMI). Position of the piston furthest from the cylinder head.
- Diameter (in English: Bore). Inside diameter of the cylinder. Generally expressed in millimeters (mm).
- Career (in English: Stroke). It includes the distance between the PMS and PMI, it is equal, with few exceptions, to twice the radius of the crank of the crankshaft. It is generally expressed in mm.
- Total volume of the cylinder (V 1 ). It is the space between the cylinder head and the piston when it is in the PMI. It is generally expressed in cm 3
- Combustion chamber volume (V 2 ). It is between the cylinder head and the piston when it is in the PMS It is usually expressed in cm 3
- Volume dislodged by the piston or displacement (V 1 - V 2 ). It is the generator by the piston in its reciprocating movement from the PMS to the PMI: It is usually expressed in cm 3 .
- Volumetric compression ratio ( ). This is understood to be that between the total volume of cylinder V1 and the volume of combustion chamber V2. In general, for short, it's simply called a compression ratio: