Engine piston: design features. Rotary piston engine description photo video history Compression of the working medium

• ensures the transfer of mechanical forces to the connecting rod;
• is responsible for sealing the fuel combustion chamber;
• ensures timely removal of excess heat from the combustion chamber

The operation of the piston takes place in difficult and in many ways dangerous conditions - with increased temperature conditions and increased loads, therefore it is especially important that pistons for engines are distinguished by efficiency, reliability and wear resistance. That is why, for their production, light, but super-strong materials are used - heat-resistant aluminum or steel alloys. Pistons are made by two methods - casting or stamping.

Piston design

The engine piston has a fairly simple design, which consists of the following parts:

Volkswagen AG

1. ICE piston head
2. Piston pin
3. Retaining ring
4. Boss
5. Connecting rod
6. Steel insert
7. Compression ring first
8. Compression ring second
9. Oil scraper ring

The design features of the piston in most cases depend on the type of engine, the shape of its combustion chamber and the type of fuel used.

Bottom

The bottom can have a different shape depending on the functions it performs - flat, concave and convex. The concave bottom provides a more efficient combustion chamber, but it contributes to more deposits during combustion. The convex shape of the bottom improves the performance of the piston, but at the same time reduces the efficiency of the combustion process of the fuel mixture in the chamber.

Piston rings

Below the bottom there are special grooves (grooves) for installation piston rings... The distance from the bottom to the first compression ring is called the fire belt.

Piston rings are responsible for a secure connection between the cylinder and piston. They provide reliable tightness due to a tight fit to the cylinder walls, which is accompanied by a stressful friction process. Engine oil is used to reduce friction. For the manufacture of piston rings, a cast iron alloy is used.

The number of piston rings that can be installed in a piston depends on the type of engine used and its purpose. Systems with one oil scraper ring and two compression rings (first and second) are often installed.

Oil scraper ring and compression rings

The oil scraper ring ensures the timely elimination of excess oil from the inner walls of the cylinder, and the compression rings prevent gases from entering the crankcase.

The first compression ring absorbs most of the inertial forces during piston operation.

To reduce the loads in many engines, a steel insert is installed in the annular groove, which increases the strength and compression ratio of the ring. Compression rings can be made in the form of a trapezoid, barrel, cone, with a cutout.

The oil scraper ring in most cases is equipped with many holes for oil drainage, sometimes with a spring expander.

Piston pin

This is a tubular part that is responsible for the reliable connection of the piston to the connecting rod. Made of steel alloy. When installing the piston pin in the bosses, it is tightly secured with special retaining rings.

The piston, piston pin and rings together create a so-called piston group engine.

Skirt

The guiding part of the piston device, which can be made in the form of a cone or barrel. The piston skirt is equipped with two bosses for connecting to the piston pin.

To reduce frictional losses, a thin layer of an antifriction substance is applied to the surface of the skirt (often graphite or molybdenum disulfide is used). The lower part of the skirt is equipped with an oil scraper ring.

A mandatory process of operation of a piston device is its cooling, which can be carried out by the following methods:

• spraying oil through holes in the connecting rod or a nozzle;
• the movement of oil along the coil in the piston head;
• supplying oil to the area of ​​the rings through the annular channel;
• oil mist

Sealing part

The sealing part and the crown are connected in the form of a piston head. In this part of the device, there are piston rings - oil scraper and compression rings. The ring passages have small holes through which the used oil enters the piston and then flows into the engine crankcase.

Overall engine piston internal combustion is one of the most heavily loaded parts, which is subjected to strong dynamic and at the same time thermal effects. This imposes increased requirements both on the materials used in the production of pistons and on the quality of their manufacture.

The main types of internal combustion engines and steam engines have one common drawback. It consists in the fact that reciprocating movement requires transformation into rotary movement. This, in turn, causes poor performance, as well as a fairly high wear rate of the parts of the mechanism included in Various types engines.

Quite a lot of people thought about how to create such a motor in which the moving elements only rotated. However, only one person managed to solve this problem. Felix Wankel, a self-taught mechanic, became the inventor of the rotary piston engine. During his life, this person did not receive any specialty or higher education. Let us consider in more detail the rotor piston engine Wankel.

Brief biography of the inventor

Felix G. Wankel was born in 1902, on August 13, in the small town of Lahr (Germany). In the First World War, the father of the future inventor died. Because of this, Wankel had to quit his studies at the gymnasium and get a job as a sales assistant in a bookstore at a publishing house. Thanks to this, he became addicted to reading. Felix studied specifications engines, automotive, mechanics independently. He drew knowledge from books that were sold in the shop. It is believed that the scheme of the Wankel engine implemented later (more precisely, the idea of ​​its creation) visited in a dream. It is not known whether this is true or not, but we can say for sure that the inventor had extraordinary abilities, a craving for mechanics and a peculiar

Advantages and disadvantages

The convertible movement of a reciprocating nature is completely absent in a rotary engine. Pressure build-up occurs in those chambers that are created by the convex surfaces of the triangular rotor and various parts of the housing. The rotor rotates by combustion. This can reduce vibration and increase rotation speed. Due to the efficiency gains thus generated, the rotary engine is much smaller than a conventional reciprocating engine of equivalent power.

A rotary engine has one main component of all of its components. This important component is called a triangular rotor, which rotates inside the stator. All three rotor points, thanks to this rotation, are in constant communication with the inner wall of the housing. With the help of this contact, combustion chambers are formed, or three volumes of a closed type with gas. When the rotor rotates inside the housing, the volume of all three formed combustion chambers changes all the time, resembling the actions of a conventional pump. All three rotor flanks work like a piston.

Inside the rotor is a small gear with external teeth that is attached to the housing. The gear, which is larger in diameter, is connected to this stationary gear, which sets the very trajectory of the rotational movements of the rotor inside the housing. The teeth in the larger gear are internal.

Due to the fact that, together with the output shaft, the rotor is connected eccentrically, the rotation of the shaft occurs in the same way as the handle will rotate the crankshaft. The output shaft will rotate three times for each of the rotor revolutions.

The rotary engine has the advantage of being light in weight. The most basic of the rotary engine blocks is small in size and weight. At the same time, the handling and characteristics of such an engine will be better. Less weight is obtained due to the fact that there is simply no need for a crankshaft, connecting rods and pistons.

The rotary engine has dimensions that are much smaller than a conventional engine of the corresponding power. Thanks to the smaller engine size, handling will be much better, and the car itself will become more spacious for both passengers and the driver.

All of the parts of the rotary engine carry out continuous rotary movements in the same direction. The change in their movement occurs in the same way as in the pistons of a traditional engine. Rotary motors are internally balanced. This leads to a reduction in the vibration level itself. Rotary motor power appears to be much smoother and more uniform.

The Wankel engine has a convex special rotor with three edges, which can be called its heart. This rotor rotates within the cylindrical surface of the stator. The Mazda rotary engine is the first rotary engine in the world, which was developed specifically for mass production. This development began in 1963.

What is RAP?

In a classic four-stroke engine, the same cylinder is used for various operations - injection, compression, combustion and exhaust. In a rotary engine, each process is performed in a separate compartment of the chamber. The effect is not much different from dividing the cylinder into four compartments for each of the operations.
In a piston engine, pressure builds up as the mixture burns, causing the pistons to move back and forth in their cylinders. The connecting rods and the crankshaft convert this pushing motion into the rotational motion needed to move the vehicle.
V rotary engine there is no rectilinear motion that would have to be translated into rotational. Pressure builds up in one of the chamber compartments causing the rotor to rotate, which reduces vibration and increases the potential RPM of the engine. The result is greater efficiency and smaller dimensions for the same power as a conventional piston engine.

How does RAP work?

The function of the piston in the RPD is performed by a three-vertex rotor, which converts the force of gas pressure into the rotational movement of the eccentric shaft. The movement of the rotor relative to the stator (outer casing) is provided by a pair of gears, one of which is rigidly fixed to the rotor, and the second to the side cover of the stator. The gear itself is fixed to the motor housing. With it, the rotor gear is meshed with a gear wheel, as it were, rolls around it.
The shaft rotates in bearings placed on the housing and has a cylindrical eccentric on which the rotor rotates. The interaction of these gears provides an expedient movement of the rotor relative to the housing, as a result of which three separate chambers of variable volume are formed. The gear ratio is 2: 3, therefore, in one revolution of the eccentric shaft, the rotor returns 120 degrees, and for a full revolution of the rotor, a full four-stroke cycle occurs in each of the chambers.

Gas exchange is regulated by the top of the rotor as it passes through the inlet and outlet ports. This design allows for a 4-stroke cycle without the use of a special valve timing mechanism.

Sealing of chambers is provided by radial and end sealing plates, pressed against the cylinder by centrifugal forces, gas pressure and tape springs. The torque is obtained as a result of the action of gas forces through the rotor on the shaft eccentric Mixing, inflammation, lubrication, cooling, starting - basically the same as in a conventional piston internal combustion engine

Mixture formation

In theory, RPD uses several types of mixture formation: external and internal, based on liquid, solid, gaseous fuels.
With regard to solid fuels, it is worth noting that they are initially gasified in gas generators, since they lead to increased ash formation in the cylinders. Therefore, gaseous and liquid fuels have become more widespread in practice.
The very mechanism of mixture formation in Wankel engines will depend on the type of fuel used.
When using gaseous fuel, it mixes with air in a special compartment at the engine inlet. The combustible mixture enters the cylinders ready-made.

The mixture is prepared from liquid fuel as follows:

1. The air mixes with the liquid fuel before entering the cylinders, where the combustible mixture enters.
2. Liquid fuel and air enter the engine cylinders separately, and they are mixed already inside the cylinder. The working mixture is obtained when they come into contact with residual gases.

Accordingly, the fuel-air mixture can be prepared outside or inside the cylinders. From this comes the separation of engines with internal or external mixture formation.

Rotary piston engine specifications

options	VAZ-4132	VAZ-415
number of sections	2	2
Engine chamber working volume, cc	1,308	1,308
compression ratio	9,4	9,4
Rated power, kW (hp) / min-1	103 (140) / 6000	103 (140) / 6000
Maximum torque, N * m (kgf * m) / min-1	186 (19) / 4500	186 (19) / 4500
The minimum speed of the eccentric shaft at Idling, min-1	1000	900
Engine weight, kg
Overall dimensions, mm
Oil consumption in% of fuel consumption
Engine resource to first overhaul, thousand km
appointment	VAZ-21059/21079	VAZ-2108/2109/21099/2115/2110

models produced

	RPD engine	Acceleration time 0-100, sec	Maximum speed, km \ h

Efficiency of a rotary piston design

Despite a number of shortcomings, studies have shown that the overall efficiency of the Wankel engine is quite high by modern standards. Its value is 40 - 45%. For comparison, for piston internal combustion engines the efficiency is 25%, for modern turbodiesels it is about 40%. The highest efficiency of piston diesel engines is 50%. Until now, scientists continue to work on finding reserves to improve the efficiency of engines.

The final efficiency of the motor operation consists of three main parts:

Research in this area shows that only 75% of the fuel is completely burned. It is believed that this problem is solved by separating the combustion and gas expansion processes. It is necessary to provide for the arrangement of special chambers under optimal conditions. Combustion should take place in a closed volume, subject to an increase in temperature and pressure, the expansion process should take place at low temperatures.

1. Mechanical efficiency (characterizes the work, the result of which was the formation of the main axle torque transmitted to the consumer).

About 10% of the motor's work is spent on driving auxiliary units and mechanisms. This flaw can be corrected by making changes to the engine design: when the main moving working element does not touch the stationary body. A constant torque arm must be present along the entire path of the main working element.

1. Thermal efficiency (an indicator reflecting the amount of thermal energy generated from the combustion of fuel, converted into useful work).

In practice, 65% of the heat energy received is escaped with exhaust gases into the external environment. A number of studies have shown that it is possible to achieve an increase in thermal efficiency in the case when the design of the engine would allow for the combustion of fuel in a heat-insulated chamber, so that from the very beginning the maximum temperature values ​​are reached, and at the end this temperature is reduced to minimum values ​​by switching on the vapor phase.

Rotary piston Wankel engine

Most cars are forced to move a piston internal combustion engine (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

1. crank mechanism;
2. gas distribution mechanism;
3. supply system;
4. cooling system;
5. Lubrication system;
6. ignition system;
7. engine management system.

crank mechanism consists of a piston, cylinder liner, connecting rod and crankshaft.

Crank mechanism:
1. Expander oil scraper ring... 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 required composition and its timely ignition in the engine cylinders.

Definition.

Piston engine- one of the variants of the internal combustion engine, which works by converting the internal energy of the burning fuel into mechanical work translational movement of the piston. The piston sets in motion when the working fluid expands in the cylinder.

The crank mechanism converts the forward motion of the piston into the rotational motion of the crankshaft.

The working cycle of the engine consists of a sequence of strokes of one-way forward strokes of the piston. Engines with two and four strokes are subdivided.

The principle of operation of two-stroke and four-stroke piston engines.

Number of cylinders in piston engines may vary depending on the design (from 1 to 24). The volume of the engine is considered to be equal to the sum of the volumes of all cylinders, the capacity of which is found by the product of the cross section and the stroke of the piston.

V piston engines of various designs, the process of fuel ignition occurs in different ways:

Electrospark discharge that forms on the spark plugs. These engines can run on both gasoline and other fuels (natural gas).

By compressing the working fluid:

V diesel engines operating on diesel fuel or gas (with a 5% addition of diesel fuel), air is compressed, and when the piston reaches the maximum compression point, fuel is injected, which ignites from contact with heated air.

Compression engines... The fuel supply to them is exactly the same as in gasoline engines... Therefore, for their operation, a special composition of fuel (with admixtures of air and diethyl ether) is required, as well as precise adjustment of the compression ratio. Compressor engines have found their way into the aircraft and automotive industries.

Incandescent engines... The principle of their operation is in many ways similar to the engines of the compression model, but it was not without design features... The role of ignition in them is performed by a glow plug, the glow of which is maintained by the energy of the fuel that burns in the previous stroke. The composition of the fuel is also special, based on methanol, nitromethane and castor oil. Such engines are used both on cars and airplanes.

Calorizing motors... In these engines, ignition occurs when the fuel comes into contact with hot parts of the engine (usually the piston crown). Open-hearth gas is used as fuel. They are used as drive motors in rolling mills.

Fuels used in piston engines:

Liquid fuel- diesel fuel, gasoline, alcohols, biodiesel;

Gases- natural and biological gases, liquefied gases, hydrogen, gaseous products of oil cracking;

Produced in the gasifier from coal, peat and wood, carbon monoxide is also used as a fuel.

The operation of piston engines.

Engine Cycles detailed in technical thermodynamics. Different cyclograms are described by different thermodynamic cycles: Otto, Diesel, Atkinson or Miller and Trinkler.

Reasons for piston engine breakdowns.

Efficiency of a piston internal combustion engine.

The maximum efficiency that was obtained on piston engine is 60%, i.e. slightly less than half of the burning fuel is spent on heating engine parts, and also comes out with heat exhaust gases... In this connection, it is necessary to equip engines with cooling systems.

Cooling systems classification:

Air CO- give off heat to the air due to the ribbed outer surface of the cylinders. Are applied
more on weak engines (tens of hp), or on powerful aircraft engines which are cooled by a fast air flow.

Liquid CO- a liquid (water, antifreeze or oil) is used as a coolant, which is pumped through the cooling jacket (channels in the walls of the cylinder block) and enters the cooling radiator, in which it is cooled by air flows, natural or from fans. Rarely, but metallic sodium is also used as a coolant, which is melted from the heat of a warming up engine.

Application.

Piston engines, due to their power range (1 watt - 75,000 kW), have gained great popularity not only in the automotive industry, but also in aircraft and shipbuilding. They are also used to drive military, agricultural and construction equipment, power generators, water pumps, chainsaws and other machines, both mobile and stationary.

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-CHPPs based on gas-piston internal combustion engines, with the help of which the problems of power supply of small residential areas or industries, are effectively solved, have become especially widespread. 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 crankshaft cars.

Rice. 6.1.

In order for the engine to work continuously, it is necessary to periodically remove the 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 - to conventional and supercharged with the help of driven blowers.
• 7. According to the use of exhaust gas heat - into conventional (without using this heat), turbocharged and combined. On turbocharged cars, the exhaust valves open slightly earlier than usual and the higher-pressure flue gases 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 machine performance. 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 four-stroke because a full cycle is carried out here 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 is injected into the cylinder through the nozzle diesel fuel, it spontaneously 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 warms 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 from combustion products, as a result, 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 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, all other things being equal, they allow 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.