Most cars are driven by a piston engine internal combustion(abbreviated ICE) with crank mechanism... This design has become widespread due to the low cost and manufacturability of production, relatively small dimensions and weight.
By the type of fuel used, the internal combustion engine can be divided into gasoline and diesel. I must say that gasoline engines work great on. This division directly affects the design of the engine.
How a piston internal combustion engine works
The basis of its design is the cylinder block. This is a body cast from cast iron, aluminum or sometimes magnesium alloy. Most of the mechanisms and parts of other engine systems are attached specifically to the cylinder block, or located inside it.
Another major part of the engine is its head. It is located at the top of the cylinder block. The head also houses parts of the engine systems.
A pallet is attached to the bottom of the cylinder block. If this part carries loads during engine operation, it is often called the oil pan, or crankcase.
All engine systems
- crank mechanism;
- gas distribution mechanism;
- supply system;
- cooling system;
- Lubrication system;
- ignition system;
- engine management system.
crank mechanism consists of a piston, cylinder liner, connecting rod and crankshaft.
Crank mechanism:
1. Oil scraper ring expander. 2. Oil scraper piston ring. 3. Compression ring, third. 4. Compression ring, second. 5. Upper compression ring. 6. Piston. 7. Retaining ring. 8. Piston pin. 9. Connecting rod bushing. 10. Connecting rod. 11. Connecting rod cover. 12. Insert of the lower head of the connecting rod. 13. Connecting rod cap bolt, short. 14. Bolt of the connecting rod cover, long. 15. Leading gear. 16. Plug of the oil channel of the connecting rod journal. 17. Crankshaft bearing shell, upper. 18. The crown is toothed. 19. Bolts. 20. Flywheel. 21. Pins. 22. Bolts. 23. Oil deflector, rear. 24. Crankshaft rear bearing cover. 25. Pins. 26. Thrust bearing half ring. 27. Crankshaft bearing shell, lower. 28. Crankshaft counterweight. 29. Screw. 30. Crankshaft bearing cover. 31. Coupling bolt. 32. Bearing cover retaining bolt. 33. Crankshaft. 34. Counterweight, front. 35. Oil separator, front. 36. Lock nut. 37. Pulley. 38. Bolts.
The piston is located inside the cylinder liner. With the help of a piston pin, it is connected to the connecting rod, the lower head of which is attached to the connecting rod journal of the crankshaft. The cylinder liner is a hole in the block, or a cast iron bushing that fits into the block.
Cylinder liner with block
The cylinder liner is closed from above with a head. The crankshaft is also attached to the block at the bottom of the block. The mechanism converts the linear motion of the piston into rotational motion of the crankshaft. The same rotation that ultimately makes the wheels of the car spin.
Gas distribution mechanism is responsible for supplying a mixture of fuel vapors and air into the space above the piston and removing combustion products through valves that open strictly at a certain point in time.
The power system is primarily responsible for preparing a combustible mixture of the desired composition. The devices of the system store fuel, clean it, mix it with air so as to ensure the preparation of a mixture of the required composition and quantity. The system is also responsible for removing combustion products from the engine.
When the engine is running, heat energy is generated in an amount greater than the engine is able to convert into mechanical energy. Unfortunately, the so-called thermal efficiency, even the best samples modern engines does not exceed 40%. Therefore, it is necessary to dissipate a large amount of "extra" heat in the surrounding space. This is exactly what it does, removes heat and maintains a stable operating temperature of the engine.
Lubrication system . This is exactly the case: "You won't grease, you won't go." Internal combustion engines have a large number of friction units and so-called plain bearings: there is a hole, a shaft rotates in it. There will be no lubrication, the unit will fail from friction and overheating.
Ignition system designed to set fire, strictly at a certain point in time, a mixture of fuel and air in the space above the piston. there is no such system. There, the fuel ignites spontaneously under certain conditions.
Video:
The engine management system uses an electronic control unit (ECU) to control and coordinate engine systems. First of all, this is the preparation of a mixture of the desired composition and its timely ignition in the engine cylinders.
Piston ICEs are most widely used as energy sources in road, rail and sea transport, in agricultural and construction industries (tractors, bulldozers), in emergency power supply systems for special facilities (hospitals, communication lines, etc.) and in many others. areas of human activity. In recent years, mini-CHP plants based on gas-piston internal combustion engines have become especially widespread, with the help of which the problems of power supply of small residential areas or industries are effectively solved. The independence of such CHPPs from centralized systems (such as RAO UES) increases the reliability and stability of their operation.
Reciprocating internal combustion engines, which are very diverse in design, are capable of providing a very wide range of powers - from very small (engine for aircraft models) to very large (engine for ocean tankers).
We have repeatedly got acquainted with the basics of the device and the principle of operation of piston internal combustion engines, starting from the school course in physics and ending with the course "Technical thermodynamics". And yet, in order to consolidate and deepen our knowledge, let us consider this issue very briefly again.
In fig. 6.1 shows a diagram of the engine device. As you know, combustion of fuel in an internal combustion engine is carried out directly in the working fluid. In piston internal combustion engines, such combustion is carried out in the working cylinder 1 with a piston moving in it 6. The flue gases generated by combustion push the piston, forcing it to do useful work. The translational movement of the piston with the help of the connecting rod 7 and the crankshaft 9 is converted into rotational, more convenient for use. The crankshaft is located in the crankcase, and the engine cylinders are located in another body part called the block (or jacket) of cylinders 2. The cylinder cover 5 contains the intake 3 and graduation 4 valves with a forced cam drive from a special camshaft, kinematically connected to the crankshaft of the machine.
Rice. 6.1.
In order for the engine to work continuously, it is necessary to periodically remove combustion products from the cylinder and fill it with new portions of fuel and oxidizer (air), which is done due to the movements of the piston and the operation of the valves.
Reciprocating internal combustion engines are usually classified according to various general characteristics.
- 1. According to the method of mixture formation, ignition and heat supply, engines are divided into machines with forced ignition and self-ignition (carburetor or injection and diesel).
- 2. According to the organization of the working process - into four-stroke and two-stroke. In the latter, the working process is completed not in four, but in two piston strokes. In turn, two-stroke internal combustion engines are subdivided into machines with direct-flow valve-slotted blowing, with crank-chamber blowing, with direct-flow blowing and oppositely moving pistons, etc.
- 3. By appointment - for stationary, ship, diesel locomotive, automobile, auto-tractor, etc.
- 4. According to the number of revolutions - to low-speed (up to 200 rpm) and high-speed.
- 5. By the average piston speed d> n =? NS/ 30 - for low-speed and high-speed (th? „> 9 m / s).
- 6. By air pressure at the beginning of compression - for conventional and pressurized with the help of driven blowers.
- 7. On the use of heat exhaust gases- for conventional (without using this heat), turbocharged and combined. On turbocharged cars, the exhaust valves open slightly earlier than usual and the flue gases at a higher pressure than usual are sent to a pulse turbine, which drives the turbocharger to supply air to the cylinders. This allows more fuel to be burned in the cylinder, improving both efficiency and specifications cars. In combined internal combustion engines, the piston part serves in many respects as a gas generator and produces only ~ 50-60% of the machine's power. The rest of the total power comes from the flue gas turbine. For this, the flue gases at high pressure R and temperature / are sent to the turbine, the shaft of which, by means of a gear transmission or a fluid coupling, transfers the received power to the main shaft of the installation.
- 8. According to the number and arrangement of cylinders, engines are: one-, two- and multi-cylinder, in-line, K-shaped, T-shaped.
Let us now consider the real process of a modern four-stroke diesel engine. It is called a four-stroke cycle because a full cycle here is carried out in four full strokes of the piston, although, as we will now see, during this time slightly more real thermodynamic processes are carried out. These processes are illustrated in Figure 6.2.
Rice. 6.2.
I - absorption; II - compression; III - working stroke; IV - ejection
During the beat suction(1) The suction (inlet) valve opens a few degrees before top dead center (TDC). The point corresponds to the opening moment G on R-^ -chart. In this case, the suction process occurs when the piston moves to the bottom dead center (BDC) and proceeds at a pressure p ns less atmospheric /; a (or boost pressure NS). When the direction of movement of the piston changes (from BDC to TDC), the intake valve does not close immediately either, but with a certain delay (at the point T). Further, when the valves are closed, the working fluid is compressed (to the point with). In diesel cars, clean air is sucked in and compressed, and in carburetor cars - a working mixture of air with gasoline vapors. This piston stroke is usually called a stroke. compression(II).
A few degrees of the angle of rotation of the crankshaft before TDC, diesel fuel is injected into the cylinder through a nozzle, it self-ignites, combustion and expansion of combustion products. In carburetor machines, the working mixture is forcibly ignited using an electric spark discharge.
When the air is compressed and the heat exchange with the walls is relatively low, its temperature rises significantly, exceeding the self-ignition temperature of the fuel. Therefore, the injected finely atomized fuel heats up very quickly, evaporates and ignites. As a result of fuel combustion, the pressure in the cylinder at first abruptly, and then, when the piston begins its path to BDC, increases with a decreasing rate to a maximum, and then, as the last portions of fuel supplied during injection are burned, it even begins to decrease (due to intensive growth cylinder volume). We will assume conditionally that at the point with" the combustion process ends. This is followed by the process of expansion of flue gases, when the force of their pressure moves the piston to the BDC. The third stroke of the piston, which includes the combustion and expansion processes, is called working stroke(III), because only at this time does the engine perform useful work. This work is accumulated by means of a flywheel and given to the consumer. Part of the accumulated work is expended in the execution of the remaining three cycles.
When the piston approaches BDC, the exhaust valve opens with some advance (point B) and the exhaust flue gases rush into exhaust pipe, and the pressure in the cylinder drops sharply to almost atmospheric. During the stroke of the piston to TDC, flue gases are pushed out of the cylinder (IV - ejection). Since the exhaust tract of the engine has a certain hydraulic resistance, the pressure in the cylinder during this process remains above atmospheric. The exhaust valve closes after TDC (point NS), so that in each cycle a situation arises when both the intake and exhaust valves are open at the same time (they speak of valve overlap). This makes it possible to better clean the working cylinder of combustion products, as a result of which the efficiency and completeness of fuel combustion increases.
The cycle is organized differently for two-stroke machines (Fig. 6.3). These are usually supercharged engines and for this they usually have a driven blower or turbocharger. 2 which, during engine operation, pumps air into the air receiver 8.
The working cylinder of a two-stroke engine always has scavenging ports 9 through which air from the receiver enters the cylinder when the piston, passing to the BDC, begins to open them more and more.
During the first stroke of the piston, which is commonly called the working stroke, the injected fuel is burned in the engine cylinder and the combustion products expand. These processes on indicator chart(fig. 6.3, a) reflected by the line c - I - t. At the point T exhaust valves open and, under the influence of excess pressure, flue gases rush into the exhaust tract 6, as a result
Rice. 6.3.
1 - suction pipe; 2 - blower (or turbocharger); 3 - piston; 4 - exhaust valves; 5 - nozzle; 6 - exhaust tract; 7 - worker
cylinder; 8 - air receiver; 9- purge windows
tate, the pressure in the cylinder drops noticeably (point NS). When the piston is lowered enough that the purge ports begin to open, compressed air rushes into the cylinder from the receiver. 8 pushing the remaining flue gases out of the cylinder. At the same time, the working volume continues to increase, and the pressure in the cylinder decreases almost to the pressure in the receiver.
When the direction of movement of the piston is reversed, the cylinder purging process continues as long as the purge ports remain at least partially open. At the point To(fig. 6.3, b) the piston completely covers the purge ports and the next portion of the air that has entered the cylinder begins to compress. A few degrees before TDC (at the point with") fuel injection begins through the nozzle, and then the processes described earlier occur, leading to the ignition and combustion of fuel.
In fig. 6.4 shows diagrams explaining the design of other types of two-stroke engines. In general, the operating cycle for all these machines is similar to that described, and the design features largely affect only the duration
Rice. 6.4.
a- loop slot blowing; 6 - direct-flow blowdown with oppositely moving pistons; v- crank-chamber blowdown
individual processes and, as a consequence, on the technical and economic characteristics of the engine.
In conclusion, it should be noted that two-stroke engines theoretically allow, ceteris paribus, to obtain twice the power, but in reality, due to the worse conditions for cleaning the cylinder and relatively large internal losses, this gain is somewhat less.
When fuel is burned, thermal energy is released. An engine in which fuel is burned directly inside the working cylinder and the energy of the resulting gases is perceived by a piston moving in the cylinder is called a piston engine.
So, as mentioned earlier, this type of engine is the main one for modern cars.
In such engines, the combustion chamber is located in a cylinder, in which the thermal energy from the combustion of the fuel-air mixture is converted into mechanical energy of the piston moving translationally and then, by a special mechanism, which is called a crank-connecting rod, is converted into rotational energy of the crankshaft.
At the place of formation of a mixture consisting of air and fuel (combustible), piston internal combustion engines are divided into engines with external and internal conversion.
At the same time, engines with external mixture formation according to the type of fuel used, they are divided into carburetor and injection, running on light liquid fuel (gasoline) and gas, running on gas (gas generator, lighting, natural gas, etc.). Compression ignition engines are diesel engines (diesels). They run on heavy fuel oil (diesel). In general, the design of the engines themselves is practically the same.
The working cycle of four-stroke piston engines occurs when crankshaft makes two turns. By definition, it consists of four separate processes (or strokes): intake (1 stroke), compression of the air-fuel mixture (2 stroke), power stroke (3 stroke) and exhaust (4 stroke).
The change in the engine operation strokes is provided with the help of a gas distribution mechanism, consisting of camshaft, a transmission system of pushers and valves that isolate the working space of the cylinder from the external environment and mainly provide a change in valve timing. Due to the inertia of gases (features of gas dynamics processes), the intake and exhaust strokes for a real engine overlap, which means their joint action. On high revs phase overlap has a positive effect on the operation of the engine. On the contrary, the higher it is at low revs, the lower the engine torque. This phenomenon is taken into account in the operation of modern engines. They create devices that allow you to change the valve timing during operation. There are various designs of such devices, the most suitable of which are electromagnetic valve timing devices (BMW, Mazda).
Carbureted internal combustion engines
V carburetor engines the air-fuel mixture is prepared before it enters the engine cylinders, in a special device - in the carburetor. In such engines, a combustible mixture (a mixture of fuel and air) that has entered the cylinders and mixed with the residual exhaust gases (working mixture) is ignited by an external source of energy - an electric spark of the ignition system.
Injection ICE
In such engines, due to the presence of spray nozzles that inject gasoline into the intake manifold, mixture formation with air occurs.
Gas internal combustion engines
In these engines, the gas pressure after exiting gas reducer is greatly reduced and brought to close to atmospheric, after which it is sucked in with the help of an air-gas mixer, injected by means of electric nozzles (similarly injection engines) into the intake manifold of the engine.
Ignition, as in previous types of engines, is carried out from the spark of a candle, slipping between its electrodes.
Diesel internal combustion engines
In diesel engines, mixture formation takes place directly inside the engine cylinders. Air and fuel enter the cylinders separately.
At the same time, at first only air enters the cylinders, it is compressed, and at the moment of its maximum compression, a stream of finely atomized fuel is injected into the cylinder through a special nozzle (the pressure inside the cylinders of such engines reaches much higher values than in engines of the previous type), the formed mixtures.
In this case, the mixture is ignited as a result of an increase in the temperature of the air with its strong compression in the cylinder.
Among the disadvantages diesel engines it is possible to distinguish a higher, in comparison with the previous types of piston engines, the mechanical stress of its parts, especially the crank mechanism, which requires improved strength properties and, as a result, larger dimensions, weight and cost. It is increased due to the complicated design of engines and the use of better materials.
In addition, such engines are characterized by inevitable soot emissions and an increased content of nitrogen oxides in the exhaust gases due to the heterogeneous combustion of the working mixture inside the cylinders.
Gas-diesel internal combustion engines
The principle of operation of such an engine is similar to the operation of any of the varieties of gas engines.
The air-fuel mixture is prepared in a similar way, by supplying gas to an air-gas mixer or to the intake manifold.
However, the mixture is ignited with an ignition portion of diesel fuel, injected into the cylinder by analogy with the operation of diesel engines, and not using an electric plug.
Rotary piston internal combustion engines
In addition to the well-established name, this engine is named after the scientist-inventor who created it and is called the Wankel engine. Proposed at the beginning of the 20th century. Currently, the manufacturers Mazda RX-8 are engaged in such engines.
The main part of the engine is formed by a triangular rotor (analogue of a piston), rotating in a chamber of a specific shape, according to the design of the inner surface, reminiscent of the number "8". This rotor acts as a crankshaft piston and a gas distribution mechanism, thus eliminating the valve timing system required for piston engines. It performs three full working cycles in one revolution, which allows one such engine to replace a six-cylinder piston engine. positive qualities, among which also the fundamental simplicity of its design, has disadvantages that prevent its widespread use. They are associated with the creation of durable reliable seals of the chamber with the rotor and the construction of the necessary engine lubrication system. Work cycle rotary piston engines consists of four strokes: intake of the air-fuel mixture (1 stroke), compression of the mixture (2 stroke), expansion of the combustion mixture (3 stroke), exhaust (4 stroke).
Rotary combustion internal combustion engines
This is the same engine used in the Yo-mobile.
Gas turbine internal combustion engines
Already today, these engines are successfully able to replace piston internal combustion engines in cars. And although the design of these engines has reached this level of perfection only in the last few years, the idea of using gas turbine engines in automobiles has arisen for a long time. The real possibility of creating reliable gas turbine engines is now provided by the theory of blade engines, which has reached a high level of development, metallurgy and the technology of their production.
What is a gas turbine engine? To do this, let's look at its schematic diagram.
The compressor (item 9) and the gas turbine (item 7) are on the same shaft (item 8). The gas turbine shaft rotates in bearings (key 10). The compressor takes air from the atmosphere, compresses it and directs it into the combustion chamber (item 3). The fuel pump (item 1) is also driven by the turbine shaft. It supplies fuel to the injector (item 2), which is installed in the combustion chamber. The gaseous products of combustion enter through the guide vane (item 4) of the gas turbine onto the blades of its impeller (item 5) and force it to rotate in a given direction. Exhaust gases are released into the atmosphere through the branch pipe (item 6).
And although this engine is full of flaws, they are gradually eliminated as the design develops. At the same time, in comparison with a piston internal combustion engine, a gas turbine internal combustion engine has a number of significant advantages. First of all, it should be noted that, like a steam turbine, a gas turbine can develop high speeds. This allows you to get more power from smaller engines and lighter in weight (almost 10 times). In addition, the only type of movement in gas turbine is rotational. A piston engine, in addition to a rotary engine, has reciprocating piston movements and complex connecting rod movements. Also, gas turbine engines do not require special cooling and lubrication systems. The absence of significant friction surfaces with a minimum number of bearings ensures long-term operation and high reliability gas turbine engine... Finally, it is important to note that their nutrition is carried out using kerosene or diesel fuel, i.e. cheaper types than gasoline. The reason that restrains the development of automobile gas turbine engines is the need to artificially limit the temperature of the gases entering the turbine blades, since high-fire metals are still very expensive. As a result, it reduces the useful use (efficiency) of the engine and increases the specific fuel consumption (the amount of fuel per 1 hp). For passenger and cargo car engines the gas temperature has to be limited to within 700 ° C, and in aircraft engines up to 900 ° C. However, today there are some ways to increase the efficiency of these engines by removing the heat of the exhaust gases to heat the air entering the combustion chambers. The solution to the problem of creating a highly efficient automobile gas turbine engine largely depends on the success of work in this area.
Combined internal combustion engines
A great contribution to the theoretical aspects of the operation and creation of combined engines was made by the engineer of the USSR, Professor A.N. Shelest.
Alexey Nesterovich Shelest
These engines are a combination of two machines: reciprocating and vane, which can be a turbine or compressor. Both of these machines are important elements workflow. As an example of such a turbocharged engine. At the same time, in a conventional piston engine, air is forced into the cylinders with the help of a turbocharger, which makes it possible to increase the engine power. It is based on the use of the energy of the exhaust gas stream. It acts on the turbine impeller, which is attached to the shaft on one side. And spins it. The compressor blades are located on the other side of the same shaft. Thus, with the help of the compressor, air is pumped into the engine cylinders due to vacuum in the chamber on the one hand and forced air supply, on the other hand, a large amount of a mixture of air and fuel enters the engine. As a result, the volume of the combustible fuel increases and the resulting combustion gas occupies a larger volume, which creates a greater force on the piston.
Two-stroke internal combustion engines
This is the name of an internal combustion engine with an unusual gas distribution system. It is realized in the process of passing the reciprocating piston through two nozzles: inlet and outlet. You can find its foreign designation "RCV".
The engine's work processes take place during one crankshaft revolution and two piston strokes. The principle of operation is as follows. First, the cylinder is purged, which means the intake of the combustible mixture with the simultaneous intake of the exhaust gases. Then the working mixture is compressed, at the moment of turning the crankshaft by 20-30 degrees from the position of the corresponding BDC when moving to TDC. And the working stroke, the length of which is the piston stroke from the top dead center (TDC), before reaching the bottom dead center (BDC) by 20-30 degrees in terms of crankshaft revolutions.
There are obvious disadvantages to two-stroke engines. Firstly, the weak link in the two-stroke cycle is engine purging (again, from the point of view of gas dynamics). This happens on the one hand due to the fact that the separation of the fresh charge from the exhaust gases cannot be ensured, i.e. inevitably, losses of a fresh mixture, essentially flying into the exhaust pipe, (or air if we are talking about a diesel engine) are inevitable. On the other hand, the working stroke lasts less than half a revolution, which already indicates a decrease in the engine efficiency. Finally, the duration of the extremely important gas exchange process, which in a four-stroke engine takes up half the operating cycle, cannot be increased.
Two-stroke engines are more complex and more expensive due to the mandatory use of a purge system or a pressurization system. Undoubtedly, the increased thermal stress of the parts of the cylinder-piston group requires the use of more expensive materials for individual parts: pistons, rings, cylinder liners. Also, the performance of the gas distribution functions by the piston imposes a limitation on the size of its height, which consists of the height of the piston stroke and the height of the blowing windows. This is not so critical in a moped, but it makes the piston much heavier when installed on cars that require significant power consumption. Thus, when the power is measured in tens or even hundreds Horse power, the increase in the mass of the piston is very noticeable.
Nevertheless, some work was carried out in the direction of improving such engines. In Ricardo engines, special distribution sleeves with a vertical stroke were introduced, which was some attempt to make it possible to reduce the size and weight of the piston. The system turned out to be quite complex and very expensive to implement, so such engines were used only in aviation. It should be additionally noted that the exhaust valves (with direct-flow valve blowing) have twice the heat intensity in comparison with the valves of four-stroke engines. In addition, the seats have a longer direct contact with the exhaust gases, and therefore a worse heat dissipation.
Six-stroke internal combustion engines
The work is based on the principle of operation of a four-stroke engine. Additionally, its design contains elements that, on the one hand, increase its efficiency, while on the other hand, reduce its losses. There are two different types of these motors.
In engines operating on the basis of Otto and Diesel cycles, there are significant heat losses during fuel combustion. These losses are used in the engine of the first design as additional power. In the designs of such engines, additional air-fuel mixture is used as a working medium for the additional piston stroke, steam or air is used, as a result of which the power is increased. In these engines, after each fuel injection, the pistons move three times in both directions. In this case, there are two working strokes - one with fuel and the other with steam or air.
The following engines have been created in this area:
Bajulaz engine (from English Bajulaz). It was created by Bayulas (Switzerland);
Crower's engine (from English Crower). Invented by Bruce Crower (USA);
Bruce Crower
Velozeta Engine (from English Velozeta) Was built in the College of Engineering (India).
The principle of operation of the second type of engine is based on the use in its design of an additional piston on each cylinder and located opposite the main one. The auxiliary piston moves at a frequency that is halved in relation to the main piston, which provides six piston strokes per cycle. The additional piston, by its main purpose, replaces the traditional gas distribution mechanism of the engine. Its second function is to increase the compression ratio.
The main, independently created from each other, designs of such engines are two:
Beare Head engine. Invented by Malcolm Beer (Australia);
engine named "Charge pump" (from English. German Charge pump). Invented by Helmut Kotmann (Germany).
What will happen to the internal combustion engine in the near future?
In addition to those indicated at the beginning of the article ICE disadvantages there is one more fundamental drawback that does not allow using the internal combustion engine separately from the vehicle's transmission. Power unit the car is formed by the engine in conjunction with the car's transmission. It allows the vehicle to move at all required driving speeds. But a separate internal combustion engine develops the highest power only in a narrow range of revolutions. This is why a transmission is needed. Only in exceptional cases do they dispense with the transmission. For example, in some aircraft designs.
As mentioned above, thermal expansion is used in an internal combustion engine. But how it is applied and what function it performs, we will consider using the example of the operation of a piston internal combustion engine. An engine is an energy-power machine that converts any energy into mechanical work. Engines in which mechanical work created as a result of the conversion of thermal energy, called thermal. Thermal energy is obtained by burning any kind of fuel. A heat engine, in which part of the chemical energy of the fuel combusted in the working cavity is converted into mechanical energy, is called a piston internal combustion engine. (Soviet encyclopedic dictionary)
3. 1. Classification of internal combustion engines
As mentioned above, ICEs, in which the process of fuel combustion with the release of heat and its transformation into mechanical work, takes place directly in the cylinders, is the most widespread as power plants for cars. But in most modern cars, internal combustion engines are installed, which are classified according to various criteria: By the method of mixture formation - engines with external mixture formation, in which the combustible mixture is prepared outside the cylinders (carburetor and gas), and engines with internal mixture formation (the working mixture is formed inside the cylinders) -diesels; By the way of carrying out the working cycle - four-stroke and two-stroke; By the number of cylinders - single-cylinder, double-cylinder and multi-cylinder; According to the arrangement of the cylinders - engines with a vertical or inclined arrangement of cylinders in one row, V-shaped with an arrangement of cylinders at an angle (with an arrangement of cylinders at an angle of 180, the engine is called an engine with opposite cylinders, or opposed); By cooling method - for engines with liquid or air cooled; By the type of fuel used - gasoline, diesel, gas and multi-fuel; By the compression ratio. Depending on the degree of compression, a distinction is made between
engines of high (E = 12 ... 18) and low (E = 4 ... 9) compression; By the method of filling the cylinder with a fresh charge: a) naturally aspirated engines, in which air or a combustible mixture is injected due to vacuum in the cylinder during the suction stroke of the piston;) supercharged engines, in which air or a combustible mixture is injected into the working cylinder under pressure, created by the compressor, in order to increase the charge and obtain increased engine power; According to the frequency of rotation: low-speed, high-speed, high-speed; By purpose, stationary engines are distinguished, auto tractor, ship, diesel, aviation, etc.
3.2. Basics of a piston internal combustion engine
Reciprocating internal combustion engines consist of mechanisms and systems that perform their assigned functions and interact with each other. The main parts of such an engine are the crank mechanism and the gas distribution mechanism, as well as the power supply, cooling, ignition and lubrication systems.
The crank mechanism converts the rectilinear reciprocating motion of the piston into rotational motion of the crankshaft.
The gas distribution mechanism ensures the timely admission of the combustible mixture into the cylinder and the removal of combustion products from it.
The power system is designed for the preparation and supply of a combustible mixture into the cylinder, as well as for the removal of combustion products.
The lubrication system serves to supply oil to the interacting parts in order to reduce the friction force and partially cool them, along with this, the oil circulation leads to the washing off of carbon deposits and the removal of wear products.
The cooling system maintains a normal operating temperature of the engine, providing heat removal from the parts of the cylinders of the piston group and the valve mechanism that are very hot during the combustion of the working mixture.
The ignition system is designed to ignite the working mixture in the engine cylinder.
So, a four-stroke piston engine consists of a cylinder and a crankcase, which is closed from below by a sump. Inside the cylinder, a piston with compression (sealing) rings moves, in the form of a glass with a bottom in the upper part. The piston is connected through a piston pin and a connecting rod to the crankshaft, which rotates in the main bearings located in the crankcase. The crankshaft consists of main journals, cheeks and connecting rod journals. The cylinder, piston, connecting rod and crankshaft make up the so-called crank mechanism. From above, the cylinder is covered with a head with valves, the opening and closing of which is strictly coordinated with the rotation of the crankshaft, and, consequently, with the movement of the piston.
The movement of the piston is limited to two extreme positions at which its speed is zero. The topmost position of the piston is called top dead center (TDC), its bottommost position is the bottom dead center (BDC).
The non-stop movement of the piston through the dead center is provided by a flywheel in the form of a disk with a massive rim. The distance traveled by the piston from TDC to BDC is called the piston stroke S, which is equal to twice the radius R of the crank: S = 2R.
The space above the piston crown when it is at TDC is called the combustion chamber; its volume is denoted by Vc; the space of the cylinder between two dead points (BDC and TDC) is called its working volume and is denoted by Vh. The sum of the volume of the combustion chamber Vc and the working volume Vh is the total volume of the cylinder Va: Va = Vc + Vh. The working volume of the cylinder (it is measured in cubic centimeters or meters): Vh = pD ^ 3 * S / 4, where D is the cylinder diameter. The sum of all the working volumes of the cylinders of a multi-cylinder engine is called the working volume of the engine, it is determined by the formula: Vр = (pD ^ 2 * S) / 4 * i, where i is the number of cylinders. The ratio of the total volume of the cylinder Va to the volume of the combustion chamber Vc is called the compression ratio: E = (Vc + Vh) Vc = Va / Vc = Vh / Vc + 1. Compression ratio is an important parameter for internal combustion engines because greatly affects its efficiency and power.
In the cylinder-piston group (CPG), one of the main processes takes place, due to which the internal combustion engine functions: the release of energy as a result of combustion of the air-fuel mixture, which is subsequently converted into a mechanical action - the rotation of the crankshaft. The main working component of the CPG is the piston. Thanks to him, the conditions necessary for the combustion of the mixture are created. The piston is the first component involved in the conversion of the received energy.
The engine piston is cylindrical in shape. It is located in the cylinder liner of the engine, it is a movable element - during operation, it reciprocates and performs two functions.
- When moving forward, the piston reduces the volume of the combustion chamber, compressing the fuel mixture, which is necessary for the combustion process (in diesel engines ignition of the mixture does occur from its strong compression).
- After ignition of the air-fuel mixture in the combustion chamber, the pressure rises sharply. In an effort to increase the volume, it pushes the piston back, and it makes a return movement, which is transmitted through the connecting rod to the crankshaft.
What is the piston of an internal combustion engine of a car?
The device of the part includes three components:
- Bottom.
- Sealing part.
- Skirt.
These components are available both in one-piece pistons (the most common option) and in component parts.
Bottom
The bottom is the main working surface, since it, the walls of the liner and the head of the block form a combustion chamber in which the fuel mixture is burned.
The main parameter of the bottom is its shape, which depends on the type of internal combustion engine (ICE) and its design features.
In two-stroke engines, pistons are used with a spherical bottom - a bottom protrusion, this increases the efficiency of filling the combustion chamber with a mixture and removing exhaust gases.
In four-stroke gasoline engines the bottom is flat or concave. Additionally, technical recesses are made on the surface - recesses for valve discs (eliminate the likelihood of a piston colliding with the valve), recesses to improve mixture formation.
In diesel engines, the grooves in the bottom are the most dimensional and have a different shape. These recesses are called a piston combustion chamber and are designed to create turbulence in the flow of air and fuel into the cylinder for better mixing.
The sealing part is designed to install special rings (compression and oil scraper), the task of which is to eliminate the gap between the piston and the liner wall, preventing the breakthrough of working gases into the sub-piston space and lubricants into the combustion chamber (these factors reduce the efficiency of the motor). This ensures heat transfer from the piston to the liner.
Sealing part
The sealing part includes grooves in the cylindrical surface of the piston - grooves located behind the bottom, and bridges between the grooves. In two-stroke engines, special inserts are additionally placed in the grooves, into which the ring locks abut. These inserts are necessary to eliminate the possibility of the rings turning and getting their locks into the inlet and outlet ports, which can cause them to collapse. 
The jumper from the bottom edge to the first ring is called the head land. This belt takes on the greatest temperature effect, so its height is selected based on the operating conditions created inside the combustion chamber and the material of the piston.
The number of grooves made on the sealing part corresponds to the number piston rings(and they can be used 2 - 6). The most common design is with three rings - two compression rings and one oil scraper.
In the groove under oil scraper ring holes are made for the oil drain, which is removed with a ring from the wall of the sleeve.
Together with the bottom, the sealing part forms the piston head.
You will also be interested in:
Skirt
The skirt acts as a guide for the piston, preventing it from changing position relative to the cylinder and providing only the reciprocating movement of the part. Thanks to this component, a movable connection of the piston with the connecting rod is carried out.
For connection, holes are made in the skirt for installing the piston pin. To increase the strength at the point of contact of the finger, special massive beads, called bosses, are made on the inside of the skirt.
To fix the pin in the piston, grooves for retaining rings are provided in the mounting holes for it.
Types of pistons
In internal combustion engines, two types of pistons are used, differing in design - one-piece and composite.
Solid parts are made by casting followed by machining. In the process of casting, a blank is created from metal, which is given the general shape of the part. Further, on metal-working machines in the resulting workpiece, the working surfaces are processed, grooves for rings are cut, technological holes and grooves are made.
V constituent elements the head and skirt are separated, and they are assembled into a single structure during the installation process on the engine. Moreover, the assembly into one piece is carried out when the piston is connected to the connecting rod. For this, in addition to the holes for the finger in the skirt, there are special eyelets on the head.
The advantage of composite pistons is the ability to combine materials of manufacture, which increases the performance of the part.
Manufacturing materials
Aluminum alloys are used as the material of manufacture for solid pistons. Parts made of such alloys are characterized by low weight and good thermal conductivity. But at the same time, aluminum is not a high-strength and heat-resistant material, which limits the use of pistons made of it.
Cast pistons are also made of cast iron. This material is durable and resistant to high temperatures. Their disadvantage is their significant mass and poor thermal conductivity, which leads to strong heating of the pistons during engine operation. Because of this, they are not used on gasoline engines, since the high temperature causes glow ignition (the air-fuel mixture ignites from contact with hot surfaces, and not from the spark of the spark plug).
The design of the compound pistons allows the specified materials to be combined with each other. In such elements, the skirt is made of aluminum alloys, which provides good thermal conductivity, and the head is made of heat-resistant steel or cast iron.
But elements of a composite type also have disadvantages, including:
- the ability to use only in diesel engines;
- more weight compared to cast aluminum;
- the need to use piston rings made of heat-resistant materials;
- higher price;
Due to these features, the scope of use of compound pistons is limited, they are used only on large-sized diesel engines.
Video: The principle of the engine piston. Device
