What the internal engine consists of. The principle of operation of piston engines. Oil scraper ring and compression rings
The piston is one of the elements of the crank mechanism on which the principle of operation of many internal combustion engines is based. This article discusses the design and features of these parts.
Definition
A piston is a part that performs reciprocating movements in a cylinder and provides for the conversion of gas pressure changes into mechanical work.
Engine characteristic curves. Although the radius of the crank is constant, this moment varies with angle α. When the engine is running at a given rotation, you get a positive average moment, which is popularly called simply torque. Indicated power: power generated in the piston head; Friction power is the power consumed by the internal resistances of the engine; Effective Power This is the power measured on the motor shaft.
The figure below shows the distribution of power and motor outputs. Basically, it consists of a rotor and a stator with a connecting element between them, which can be water or an electric current, called a hydraulic dynamometer or an electric dynamometer, respectively. When we accelerate the engine, its rotation tends to increase. By tightening the adjustable belt, the engine flywheel is braked, providing dynamic balance, thereby maintaining constant rotation.
Appointment
With the participation of these parts, the thermodynamic process of the motor is implemented. Since the piston is one of the elements of the crank mechanism, it perceives the pressure produced by the gases and transfers the force to the connecting rod. In addition, it provides sealing of the combustion chamber and heat removal from it.
Design
A piston is a three-component part, that is, its design includes three components that perform various functions, and two parts: a head, which combines the bottom and the sealing part, and the guide part, represented by a skirt. 
Due to the action of the engine, a force appears on the lever, which will be read on the counter. Water admitted to the casing passes through holes in the alveoli, reaching the rotor. The centrifugal force caused by the rotational movement of the rotor imparts movement to the water, causing it to return to the alveoli of the membrane. This turbulent movement will be maintained as the rotor rotates. The power of the engine under test is absorbed by a continuous stream of water through a dynamometer. Energy absorption is manifested in an increase in water temperature, which should be available in sufficient quantity to absorb maximum power.
Bottom
It can have a different shape depending on many factors. For example, the configuration of the piston bottom of an internal combustion engine is determined by the location of other structural elements, such as nozzles, candles, valves, the shape of the combustion chamber, the features of the processes occurring in it, the general engine design, etc. In any case, it determines the features of functioning. 
Parametric dynamometer It has a rotor in the form of a gear made of a material with high magnetic permeability, and the same material in two rings made in a single unit with the stator, separated from the rotor by a small free space. In the center of the rotor there is a coil operating from a direct current. When turned on, the coil generates a magnetic field that is concentrated in the teeth of the rotor, which rotates, generating stray currents in the rings, which thus heat up. The generated heat is absorbed by the stator and removed from it using an adequate cooling system, water.
Two main types of piston head configuration are distinguished: convex and concave. The first provides greater strength, but worsens the configuration of the combustion chamber. With a concave shape of the bottom, the combustion chamber, on the contrary, has an optimal shape, but carbon deposits are more intensively deposited. Less commonly (in two-stroke engines) there are pistons with a bottom represented by a protrusion of the reflector. This is necessary when purging for the directional movement of combustion products. Parts of gasoline engines usually have a flat or almost flat bottom. Sometimes there are grooves in them to fully open the valves. For direct injection engines, the pistons are characterized by a more complex configuration. In diesel engines, they are distinguished by the presence of a combustion chamber in the bottom, which provides a good turbulence and improves mixture formation.
This dynamometer can be controlled by the intensity of the current passing through the coil. DC Dynamometer This dynamometer depends on the need, generator or electric motor. Its body is suspended in coaxial bearings. The magnetic field of this dynamometer has an independent excitation that changes the field and rotor feed if it receives a wide range of speeds and absorbed powers. The brake effect option is just a rheostat.
Using the balance scale as a reference, when the pointer passes the known value, the stopwatch starts, and when the pointer changes to the known value, the stopwatch turns off. Then we will consume mass for a certain time, which is a mass flow of fuel consumed. Volume Method A rotor is used in the fuel supply line for the engine, which will directly supply the amount of fuel consumed per unit of time. The disadvantage of this method is that it is necessary to know the specific gravity of the fuel, determined at the mass flow rate.
Most pistons are unilateral, although there are bilateral options that have two bottoms.
The distance between the groove of the first compression ring and the bottom is called the piston fire zone. The value of its height, which is different for parts from different materials, is very important. In any case, exceeding the height of the ring of fire beyond the minimum permissible value may result in burnout of the piston and deformation of the seat of the upper compression ring.
Air flow measurement The figure shows equipment that uses a diaphragm to measure air flow. The basic principle of operation: As you know, the air inlet into the engine is pulsating, and not a constant flow, in order to solve this problem, air is sucked into the engine in the tank, which, due to its size, eliminates pulsation, resulting in a constant air flow through the hole .
Its meaning will serve as a reference. The values \u200b\u200bobtained are for reference only and may vary. This also leads to cooling of the combustion chamber and, as a consequence, to the disappearance of the flame, which impedes the movement of the engine. - Maximum power. This is a slightly enriched mixture that produces maximum power at full engine load. - Economical mixture This is a slightly weak mixture, which, due to excess air, allows you to completely burn fuel. In this state, the engine can provide a minimum specific consumption. - Very poor mixing Due to excess air, the flame becomes too slow, supporting combustion for most of the expansion, causing the combustion chamber to overheat.
Sealing part
There are oil scraper and compression rings. In parts of the first type, the channels have through holes for the oil removed from the surface of the cylinder to enter the piston from where it enters the oil pan. Some of them have a rim of corrosion-resistant cast iron with a groove for the upper compression ring.
This condition may cause the piston head to melt. When tested on a dynamometer, he showed a force reading of 11 kgf and a fuel consumption of 90 ml in 40 seconds. Then the engine was driven by a dynamometer, providing a friction power of 3, 8 kW. A sphere called the flame core is formed near the candle electrodes. The surface of the flame core is called the flame front and spreads throughout the combustion chamber facing the unburned mixture, leaving behind burnt gases. If the flame front does not experience any interference, we will have normal combustion.
Compression rings perform the task of preventing the entry of gases into the crankcase from the combustion chamber. The greatest loads are on the first of them, so in some engines its groove is reinforced with a steel insert. Compression rings can be trapezoidal, conical, barrel-shaped. Some of them have a neckline.
Factors that affect the speed of the flame front. Turbulents increase contact between particles, accelerating the reaction. The ratio of fuel to air. Lightly enriched mixtures cause a higher propagation rate. Residual gases their presence slows down combustion.
Pre-ignition does not cause an increase in pressure, but rather increases the temperature, causing the piston head to melt without any interference. Factors affecting detonation: 1 - Fuel quality - is determined by the octane number, which indicates the opposing power of the fuel, the more complex is the detonation; 2. Pressure and suction temperature - the greater the likelihood of detonation; 3 - coolant temperature - a high probability of detonation; 4. Flame trajectory - the larger the trajectory, the greater the probability of detonation, which limits the cylinder diameter to low values, rarely exceeds 10 cm; 5.
The oil scraper ring is used to remove excess oil from the cylinder and prevents it from entering the combustion chamber. There are holes in it for this. Some options have a spring expander.
Guide part (skirt)
Has a barrel-shaped (curved) or conical shape to compensate for thermal expansion. On it are two tides for the piston pin. In these areas, the skirt has the largest mass. In addition, there are observed the highest temperature deformations during heating. Various measures are used to reduce them. An oil scraper ring may be located at the bottom of the skirt. 
Air-fuel mixture - poor or rich mixtures, away from the stoichiometric mixture, prevent detonation; 6 - Compression speed - the greater the likelihood of detonation; 7 - Turbulence - the higher the lower the probability of detonation, heat transfer is facilitated; 8 - Spark progress - the more, the more often detonation occurs; 9 - Candle electrode temperature - hot candle, more likely detonation, cold candle, less likely detonation; 10 - Combustion chamber geometry — The conformation of the chamber has a large effect on detonation.
It is desirable that the mass of the mixture to be burned at the end of combustion. As you can see, in the engine with spontaneous combustion there are two delays, physical and chemical, which is a complete deceleration during which the fuel is injected without a significant increase in pressure and temperature in the chamber. If the delay lasts longer than usual, it accumulates fuel in the chamber, and when lit, it causes a sudden increase in pressure, causing detonation. When engines ignite spontaneously, detonation occurs at the beginning of combustion, while in engines with spark ignition this occurs at the end.
To transfer the force from the piston or to it, the most often used crank or rod. A piston pin is used to connect this part with them. It consists of steel, has a tubular shape and can be installed in several ways. Most often, a floating finger is used, which can rotate during operation. To prevent displacement, it is fixed with retaining rings. Rigid fastening is used much less frequently. The rod in some cases acts as a guide device, replacing the piston skirt.
Smoother engine operation; Higher rotations; Cold cold start. Does not create high turbulence; The movement becomes highly turbulent on the piston head, where combustion is completed; Smoother engine operation; Higher rotations; Cold cold start.
Characteristic curve of engine needs. When the throttle is open, there will be an increase in air flow through the main carburetor system, which will lead to excessive impoverishment. To avoid this, there are so-called holes for progression, which allow the rich mixture to enter with air, which leads to a gradual impoverishment in the passage from low to medium loads. With the increase in butterfly opening, the trend is that the mixture is getting richer and richer.
Materials
An engine piston may consist of various materials. In any case, they should possess such qualities as high strength, good thermal conductivity, antifriction properties, corrosion resistance and low linear expansion coefficient and density. For the production of pistons, aluminum alloys and cast iron are used.
This system is designed to prevent this enrichment. When fuel is sucked in using a venturi, a mixing tube with a series of openings allows air to enter, measured by the jet, along with the fuel, making the final mixture lean. Maximum auxiliary power system To achieve maximum engine power, the mixture must be rich. In a system with a closed butterfly valve, the chamber is exposed to high vacuum, which closes the diaphragm valve.
With a butterfly close to the full diaphragm, the vacuum in the chamber decreases, causing the spring to open the valve, allowing you to send additional fuel to the main system, enriching the mixture. Fast Accelerated Auxiliary System To prevent sudden depletion of the mixture by opening the throttle very quickly, the numeric system shows that when the throttle moves in the direction of the hole, the diaphragm is compressed by the mechanism, causing pressure in the chamber to increase, closing the valve and opening the valve, allowing a large amount of fuel to be supplied. to the main system through the injector.
Cast iron
It is distinguished by great strength, wear resistance and low. The last property provides the possibility of operation of such pistons with small gaps, due to which a good cylinder seal is achieved. However, due to the significant specific gravity, cast-iron parts are used only in those engines where the reciprocating masses have inertia forces that make up no more than a sixth of the pressure forces on the bottom of the gas piston. In addition, due to the low thermal conductivity, the heating of the bottom of the cast-iron parts during engine operation reaches 350-450 ° C, which is especially undesirable for carburetor options, as it leads to glow ignition. 
When it moves into the throttle in the closing direction, the spring returns to the diaphragm, causing the pressure in the chamber to decrease, closing the valve and opening the valve, allowing fuel to enter the chamber. The diagram below shows a complete carburetor, i.e. with all auxiliary systems.
The carburetor mixer bolt must be airtight or have openings for the adjustment range. Fatty gas emissions should be zero in any operating mode. This cycle can occur 2 or 4 times. Objectives Describe how the Otto engines work. Cycle Identify the main components of the engine.
Aluminum
This material is used most often for pistons. This is explained by a small specific gravity (aluminum parts are 30% lighter than cast iron), high thermal conductivity (3-4 times more than cast iron), which ensures heating of the bottom to no more than 250 ° C, which allows increases the degree of compression and provides better filling of the cylinder, and high anti-friction properties. At the same time, aluminum has 2 times more than that of cast iron,linear expansion coefficientthat forces you to do biggaps with cylinder walls,i.e. piston sizes less aluminum than cast irona, for identical cylinders.
In addition, such detailsand sweep lower strength, especially in the heated state (at 300 ° C it decreases by 50-55%, whereas in cast ironny - on 10%). 
Alternative Internal Combustion Engines Part 1 Introduction Gas Power Systems: Gas Turbines Alternative Engines Gas cycles simulate these systems. Although they really do not work. Internal combustion engines 1.
You can also calculate this energy with. Cycles of operation Alternative engines: the piston moves back and forth inside the transmitting power of the cylinder to rotate the axis using a connecting rod and crank system. The flow rate is almost constant regardless of the set pressure. Basic types: single screw. Double screw. Advantages over alternatives: smaller size. Reduce the number of moving parts. Disadvantages compared to alternative ones. Smaller ones.
To reduce the degree of friction, the piston walls are coated with graphite and molybdenum disulfide.
Heat
As mentioned, during the operation of the engine, the pistons can heat up to 250-450 ° C. Therefore, it is necessary to take measures aimed at both reducing heat and compensating for the thermal expansion of parts caused by it.
To cool the pistons, oil is used, which is fed into them in various ways: they create oil mist in the cylinder, spray it through the hole in the connecting rod or nozzle, inject it into the annular channel, and circulate through the tubular coil in the piston bottom.
To compensate for temperature deformationsin tidal areasskirts on both sides metal 0.5-1.5 mm deepin the form of U- or T-shaped slots. Such a measure improveslubricates and prevents from thermal deformation of scoring, therefore, the datae recesses are called refrigerators.Them used in combination with a cone-shaped or barrel-shaped skirt.It makes up for herlinear expansion due to the fact that when heatedthe skirt takes on a cylindrical shape. In addition, compensation inserts are used.so that the piston diameter experiences limited thermal expansion in the swing plane of the connecting rod. You can also isolate the guide portion from the head experiencing the greatest heat. Finally, the walls of the skirt give spring properties byapplying an oblique incision along its entire length.
Production technology
According to the manufacturing method, the pistons are divided into cast and forged (stamped).Details of the first typeused on most cars, and replacing forged pistons is used in tuning. Forged options are characterized by increased strength and durability, as well as lower weight. Therefore, the installation of pistons of this type increases the reliability and performance of the engine.This is especially important for motors operating under high loads, while cast parts are sufficient for everyday use. 
Application
A piston is a multifunctional part. Therefore, it is used not only in engines. For example, there is a brake caliper piston,as it functions in a similar way. Also the crank mechanism is used on some models of compressors, pumps and other equipment.
The internal combustion engine is today the main type of automobile engine. It is installed on all types of vehicles, from scooters and motorcycles to large-capacity trucks carrying out container transportation, dump trucks, etc. An internal combustion engine (ICE) is a device for converting chemical energy of fuel into mechanical work.
ICEs are divided into main types:
Piston engine;
- rotary piston engine;
- gas turbine engine.
Of the listed types, the most common is a piston ICE, therefore, the device and the principle of operation will be examined by its example.
The advantages of a piston internal combustion engine, ensuring its widespread use, are:
Autonomy;
- versatility (combination with various consumers);
- low cost;
- low mass;
- compactness;
- the ability to quickly launch;
- multi-fuel.
But internal combustion engines have a number of significant disadvantages, which include:
Exhaust toxicity;
- high noise level;
- low coefficient of performance;
- high speed of the crankshaft;
- low resource.
Depending on the type of fuel used, the following piston ICEs are distinguished:
Gasoline engines;
- diesel engines.
As alternative fuels used in internal combustion engines, use natural gas, alcohol fuels - ethanol and methanol, hydrogen.
The piston engine has the following general arrangement:
Housing;
- crank mechanism;
- gas distribution mechanism;
- fuel system;
- intake system;
- ignition system (gasoline engines);
- Lubrication system;
- cooling system;
- exhaust system;
- control and management system.
The engine housing combines a cylinder block and a cylinder head. The crank mechanism is designed to convert the reciprocating motion of the piston into the rotational motion of the crankshaft. The gas distribution mechanism provides the supply to the cylinders of the fuel-air mixture and the release of exhaust gases.
The intake system is designed to supply air to the engine. The fuel system delivers fuel to the engine. The joint work of these systems ensures the formation of a fuel-air mixture. The fuel system is based on an injection system.
The ignition system provides forced ignition of the fuel-air mixture in gasoline engines. In diesel engines, due to a higher compression ratio, self-ignition of the mixture occurs.
The role of the lubrication system is to reduce friction between the mating parts of the engine. The cooling of engine parts heated during operation is performed by the cooling system. Important functions of exhaust gas removal from the engine cylinders, reducing their noise and toxicity are provided by the exhaust system.
The engine management system provides electronic control of the operation of internal combustion engine systems.
The principle of operation of an internal combustion engine is based on the effect of thermal expansion of gases that occurs during the combustion of a fuel-air mixture, which ensures movement of the piston in the cylinder.
The operation of the piston engine is carried out cyclically. Each duty cycle takes place over two revolutions of the crankshaft and includes four clock cycles (four-stroke engine):
Inlet;
- compression;
- working stroke;
- release.
During the intake and working strokes, the piston moves down, and the compression and exhaust strokes move up. Duty cycles in each of the engine cylinders do not coincide in phase, thereby achieving uniform engine operation. In some ICE designs, the duty cycle is implemented in two cycles - compression and stroke (two-stroke engine).
At the intake stroke, the intake and fuel systems provide the formation of a fuel-air mixture. Depending on the design, the fuel mixture is formed in the intake manifold (central and distributed injection of gasoline engines) or directly in the combustion chamber (direct injection of gasoline and diesel engines). When opening the intake valves of the gas distribution mechanism, air or the fuel-air mixture due to the vacuum that occurs when the piston moves down, is fed into the combustion chamber.
At the compression stroke, the intake valves close and the air-fuel mixture is compressed in the engine cylinders.
The stroke of the stroke is accompanied by ignition of the fuel-air mixture. As a result of the fire, a large amount of thermal gases is formed, which press on the piston and make it move down. The movement of the piston by means of a crank mechanism is converted into rotational motion of the crankshaft, which in turn is used to move the car.
At the exhaust stroke, the exhaust valves open and the exhaust gases are removed from the cylinders to the exhaust system, where they are cleaned, cooled and reduced in noise.
The considered principle of operation of the internal combustion engine allows us to understand why the internal combustion engine has a small coefficient of efficiency - about 40%. At a particular point in time, as a rule, useful work is performed only in one cylinder, and in the others, they provide the following measures: inlet, compression, and release.