As mentioned above, the thermal expansion is applied in ICA. But how it applies and what function we will consider on the example of the work of the piston engine. The engine is called a power-based machine that transforms any energy into mechanical work. Engines in which mechanical work It is created as a result of the transformation of thermal energy, called thermal. Thermal energy is obtained when burning any fuel. The heat engine in which part of the chemical energy of fuel burning in the working cavity is converted into mechanical energy, is called a piston engine internal combustion. (Soviet Encyclopedic Dictionary)
3. 1. Classification of DVS
As it was described above, in the quality of the energy installations of cars, the Most DVS was carried out, in which the process of combustion of fuel with the release of heat and the transformation into mechanical work occurs directly in the cylinders. But in most modern cars installed internal combustion engines, which are classified according to various features: according to the mixing method - the 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 operating mixture is formed inside the cylinders) -Dizels; According to the method of carrying out the working cycle - four-stroke and two-strokes; In terms of the number of cylinders - single-cylinder, two-cylinder and multi-cylinder; By the location of the cylinders - engines with a vertical or inclined position of cylinders into one row, V-shaped with the arrangement of cylinders at an angle (at the arrangement of cylinders at an angle of 180, the engine is called an engine with opposite cylinders, or opposite); By cooling method - on the engines with liquid or air cooled; According to the type of fuel used - gasoline, diesel, gas and multi-fuel; according to the degree of compression. Depending on the degree of compression distinguishes
high (E \u003d 12 ... 18) and low (E \u003d 4 ... 9) compression; According to the method of filling the cylinder with a fresh charge: a) Engines without boost, in which air intake or combustible mixture It is carried out due to the discharge in the cylinder with the suction period of the piston;) Superior engines in which the air intake or combustible mixture into the working cylinder occurs under pressure generated by the compressor, in order to increase the charge and obtaining increased engine power; By frequency of rotation: a low-speed, increased rotational speed, high-speed; on purpose distinguishes stationary engines, car tractor, ship, diesel, aviation, etc.
3.2. Basics of the device of piston engine
Piston DVS consists of mechanisms and systems that perform the functions given to them and interacting with each other. The main parts of such an engine are the crank-connecting mechanism and gas distribution mechanism, as well as power systems, cooling, ignition and lubrication system.
The crank-connecting mechanism converts a straight line return-translational movement of the piston in the rotational motion crankshaft.
The gas distribution mechanism provides a timely inlet of a combustible mixture into a cylinder and removing combustion products from it.
The power system is designed to prepare and supply a combustible mixture into a cylinder, as well as to remove combustion products.
The lubrication system is used to supply oil to interacting parts in order to reduce the force of friction and partial cooling them, along with this, the circulation of oil leads to a washing of nagar and removing wear products.
The cooling system supports the normal temperature mode of the engine, providing heat dissipation from the work mixture of the cylinders of the piston group and the valve mechanism heavily heated when combustion.
The ignition system is designed to ignite the working mixture in the engine cylinder.
So, four-stroke piston Engine Consists of a cylinder and crankcase, which is closed at the bottom. Inside the cylinder moves the piston with compression (sealing) rings having a shape of a glass with a bottom at the top. The piston through the piston finger and the connecting rod is associated with the crankshaft, which rotates in the indigenous bearings located in the crankcase. The crankshaft consists of indigenous shekes, cheeks and rod cervical. Cylinder, piston, rod and crankshafts make up the so-called crank-connecting mechanism. From above, the cylinder covers the head with the valves, the opening and closure of which is strictly coordinated with the rotation of the crankshaft, and therefore with the movement of the piston.
The movement of the piston is limited to two extreme positions in which its speed is zero. The extreme upper position of the piston is called the upper dead point (NTC), the extreme lower position is the lower dead point (NMT).
The non-stop movement of the piston through dead dots is provided by a flywheel having a disk form with a massive rim. The distance traveled by the piston from VTC to NMT is called the piston of S, which is equal to a double radius R crank: S \u003d 2R.
The space above the bottom of the piston when it is called in the VTC called the combustion chamber; its volume is indicated via VC; The space of the cylinder between the two dead points (NMT and NTC) is called its working volume and is indicated by VH. The sum of the volume of the combustion chamber VC and the working volume VH is the full volume of the cylinder Va: VA \u003d Vc + VH. The working volume of the cylinder (it is measured in cubic centimeters or meters): VH \u003d PD ^ 3 * S / 4, where D is the diameter of the cylinder. The sum of all working volumes of the cylinders of the multi-cylinder engine is called the operating volume of the engine, it is determined by the formula: VP \u003d (PD ^ 2 * S) / 4 * i, where i is the number of cylinders. The ratio of the total volume of the VA cylinder to the volume of the combustion chamber Vc is called a compression ratio: E \u003d (VC + VH) Vc \u003d VA / Vc \u003d VH / VC + 1. The compression ratio is an important parameter of internal combustion engines, because He strongly affects its efficiency and power.
Most of the car makes it move the piston internal combustion engine (abbreviated ICC) with a crank-connecting mechanism. This design received a mass distribution due to the low cost and technological production, relatively small dimensions and weights.
By type used fuel DVS Can be divided into gasoline and diesel. I must say that gasoline engines perfectly work on. This division directly affects the engine designs.
How the piston internal combustion engine is arranged
The basis of its design is a block of cylinders. This is a housing, cast from cast iron, aluminum or sometimes magnesium alloy. Most mechanisms and details of other engine systems are attached to the cylinder block, or are located inside it.
Another major engine item is his head. It is in the upper part of the cylinder block. The head also contains the parts of the engine systems.
Bottom to the cylinder block attached pallet. If this item perceives the load when the engine is operating, it is often referred to as a crankcase pallet, or a crankcase.
All engine systems
- crank mechanism;
- gas distribution mechanism;
- supply system;
- cooling system;
- lubrication system;
- ignition system;
- engine control system.
crank mechanism Consists of a piston, cylinder sleeve, connecting rod and crankshaft.
Crank mechanism:
1. The expander of the oil-oil ring. 2. Ring piston oil. 3. Ring compression, third. 4. Ring compression, second. 5. Ring compression, top. 6. Piston. 7. Ring stop. 8. Finger piston. 9. Shutun sleeve. 10. Shatun. 11. Cover rod. 12. The liner of the lower head of the rod. 13. Bolt covers connecting rod, short. 14. Bolt covers connecting rod, long. 15. Gear lead. 16. Plug of the oil channel of the connecting rod cervical. 17. Crankshaft bearing liner, top. 18. Crown toothed. 19. Bolts. 20. Flywheel. 21. Pins. 22. Bolts. 23. Oil reflector, rear. 24. Cover rear Bearing crankshaft. 25. Pins. 26. Seafling stubborn bearing. 27. The liner of the crankshaft bearing, the bottom. 28. Advanced crankshaft. 29. Screw. 30. Crankshaft bearing cover. 31. Coupling bolt. 32. Bolt mounting bolt. 33. Shaft crankshaft. 34. Advanced, front. 35. Oil industry, front. 36. Nut Castle. 37. pulley. 38. Bolts.
The piston is located inside the cylinder sleeve. With the help of the piston finger, it is connected to the connecting rod, the lower head of which is attached to the rod crankshaft. The cylinder sleeve is a hole in the block, or the cast-iron sleeve inserted into the block.
Cylinder sleeve with block
Cylinder sleeve from above is closed by the head. The crankshaft is also attached to the block at its lower part. The mechanism converts the straightforward movement of the piston into the rotational motion of the crankshaft. The very rotation, which, ultimately, makes spinning the wheels of the car.
Gas distribution mechanism Responsible for the supply of a mixture of fuel and air vapor into space above the piston and removing combustion products through the valves opening strictly at a certain point in time.
The power system responds primarily for the preparation of a combustible mixture of the desired composition. The system devices store fuel, clean it, mixed with air so as to prepare a mixture of the desired composition and quantity. The system is also responsible for removing fuel combustion products from the engine.
When the engine is running, thermal energy is formed in an amount greater than the engine is capable of converting into mechanical energy. Unfortunately, the so-called thermal coefficient of efficiency, even the best samples modern engines does not exceed 40%. Therefore, there is a large number of "extra" warmth to disperse in the surrounding space. This is what is engaged, it takes heat and maintains the stable operating temperature of the engine.
Lubrication system . This is exactly the case: "You will not fit, you will not go." In the internal combustion engines a large number of friction nodes and so-called sliding bearings: there is a hole, the shaft rotates in it. There will be no lubricant, from friction and overheating the node will fail.
Ignition system It is designed to set fire, strictly at a certain point in time, a mixture of fuel and air in space above the piston. There is no such system. There, fuel is self-proposal under certain conditions.
Video:
Engine control system with help electronic block Management (ECU) manages engine systems and coordinates their work. First of all, it is the preparation of a mixture of the desired composition and timely igniting it in the engine cylinders.
Rotary-piston engine (RPD), or Vankel engine. Internal combustion engine developed by Felix Vankel in 1957 in collaboration with Freud Walter. In the RPD, the piston function performs a three-service (triangular) rotor, performing rotational motions inside the cavity of the complex shape. After the wave of experimental models of cars and motorcycles, which came to the 60s and 70s of the twentieth century, interest in the RPD decreased, although a number of companies continue to work on improving the design of the Vankel engine. Currently, the RPD is equipped with passenger cars mazda companies. Rotary-piston engine finds use in models.
Principle of operation
The power of gases from the burnt fuel-air mixture leads to a rotor, struck through the bearings to the eccentric shaft. The rotor movement relative to the engine housing (stator) is performed after a pair of gears, one of which, larger, is fixed on the inner surface of the rotor, the second, reference, smaller size, is rigidly attached to the inner surface of the engine side cover. The interaction of gears leads to the fact that the rotor performs circular eccentric movements, contacting the edges with the inner surface of the combustion chamber. As a result, three insulated variable volume chambers are formed between the rotor and the engine case, which occur the processes of compression of the fuel-air mixture, its combustion, the expansion of gases that have pressure on the operating surface of the rotor and cleansing the combustion chamber from the exhaust gases. The rotational motion of the rotor is transmitted to the eccentric shaft mounted on the bearings and transmitting the torque on the transmission mechanisms. Thus, two mechanical pairs are simultaneously operating in the RPD: the first is the regulating rotor movement and consisting of a pair of gears; and the second - transformative roundabout Circulation Rotor in the rotation of the eccentric shaft. The gear ratio of the gear of the rotor and stator 2: 3, so the rotor has time for one complete turnover of the eccentric shaft by 120 degrees. In turn, for one complete turnover of the rotor in each of the three chambers-formed cameras, a full four-stroke cycle of the internal combustion engine is performed.
rPD scheme
1 - inlet window; 2 graduation window; 3 - body; 4 - Camera combustion; 5 - fixed gear; 6 - rotor; 7 - gear wheel; 8 - shaft; 9 - Ignition Candle
Advantages of RPD
The main advantage of the rotor-piston engine is the simplicity of design. The RPD is 35-40 percent less details than in a piston four-stroke engine. In the RPD there are no pistons, connecting rods, crankshaft. In the "classic" version of the RPD there is no gas distribution mechanism. The air mixture enters the engine working cavity through the inlet window, which opens the rotor face. The exhaust gases are thrown through an exhaust window that crosses, again, the rotor face (it resembles the device of the gas distribution of the two-stroke piston engine).
A separate mention deserves a lubricant system, which in the simplest version of the RAP is practically absent. Oil is added to the fuel - as when operating two-stroke motorcycle engines. The grease of friction pairs (primarily the rotor and the working surface of the combustion chamber) is produced by the fuel-air mixture.
Since the mass of the rotor is small and easily balanced by a mass of counterweight eccentric shaft, RPD is characterized by a small level of vibrations and good uniformity of work. In cars with RPD it is easier to balance the engine, having achieved a minimum level of vibrations, which is well affected by the comfort of the machine as a whole. A special smoothness of the course is distinguished by two-engine motors, in which the rotors themselves are decreasing the level of vibration by balance sheets.
Another attractive quality RPD is a high specific power at high revolutions Eccentric shaft. This allows you to achieve from the car with the RPD of excellent speed characteristics with a relatively small fuel consumption. Small inertia of the rotor and increased compared to piston internal combustion engines. Specific power allows you to improve the dynamics of the car.
Finally, the important dignity of the RAP is small sizes. Rotary engine Less piston four-stroke motor of the same power is about twice. And this allows rational to use space motor compartmentMore accurately calculate the location of the transmission nodes and the load on the front and rear axle.
Disadvantages of RPD
The main disadvantage of the rotary-piston engine is the low efficiency of the gap seals between the rotor and the combustion chamber. The complex form of the RPD rotor requires reliable seals not only on thends (and four of each surface each surface - two by vertex, two on the side of the side), but also on the side surface coming into contact with the engine covers. In this case, the seals are made in the form of spring-loaded strips from high-alloyed steel with particularly accurate processing of both working surfaces and ends. Posted in the design of seals tolerances on the expansion of the metal from heating worsen their characteristics - to avoid the breakthrough of gases in the end sections of the sealing plates is almost impossible (in piston engines, the labyrinth effect is used, installing sealing rings with gaps in different directions).
In recent years, the reliability of seals has increased dramatically. Designers found new materials for seals. However, it is not yet necessary to talk about some kind of breakthrough. Seals still remain the most narrow place of the RAP.
A complex system of rotor seals requires effective lubrication rubbing surfaces. RPD consumes more oil than a four-stroke piston engine (from 400 grams to 1 kilogram per 1000 kilometers). At the same time, the oil burns along with the fuel, which is badly affected by the environmental friendliness of the motors. In the exhaust gases of the RPD dangerous to the health of people substances more than in the exhaust gases of piston engines.
Special requirements are presented to the quality of oils used in the RAP. This is due, firstly, with a tendency to elevated wear (due to the large area of \u200b\u200bcontacting parts - rotor and internal engine chamber), secondly, to overheating (again due to increased friction And due to the small size of the engine itself). For the RPD, the irregular oil change is solurally dangerous - since abrasive particles in the old oil dramatically increase engine wear, and the control of the motor. Starting a cold engine and insufficient heating lead to the fact that in the contact zone of the rotor seals with the surface of the combustion chamber and side lids, there is little lubricant. If the piston engine jars when overheated, then the RPD is most often - during the start of the cold engine (or when driving in cold weather, when cooling is redundant).
Generally working temperature RPD is higher than that of piston engines. Thermal-crimped area is a combustion chamber that has a small volume and, accordingly, an increased temperature, which makes it difficult to the fuel-air mixture (RPD due to the extended combustion chamber, prone to detonation, which can also be attributed to the disadvantages of this type of engines). Hence the demanding RPD to the quality of candles. Usually they are installed in these engines in pairs.
Rotary-piston engines with excellent power and high-speed characteristics are less flexible (or less elastic) than piston. They give out optimal power only at sufficiently high revs, which forces the designers to use the RAP in a pair with multistage CP and complicates the design automatic boxes Transmissions. Ultimately, the RAPs are not as economical as they should be in theory.
Practical application in the automotive industry
The greatest spread of the RPD was obtained in the late 60s and early 70s of the last century, when the patent for the Vankel engine was purchased by 11 leading automakers in the world.
In 1967, the German company NSU released serial a car Business class NSU RO 80. This model was produced for 10 years and divided into the world in the amount of 3,7204 copies. The car was popular, but the disadvantages of the RPD installed in it, after all, spoiled the reputation of this wonderful machine. Against the background of durable competitors, the model NSU RO 80 looked "pale" - mileage to overhaul The engine at the stated 100 thousand kilometers did not exceed 50 thousand.
Citroen, Mazda, VAZ concern, experimented with RPD. Mazda achieved the greatest success, which released his passenger car from the RAP back in 1963, four years earlier than the appearance of NSU RO 80. Today, the Mazda concern equips the RPD Sports of the RX series. Modern cars Mazda RX-8 is spared from many shortcomings of the RPD Felix Vankel. They are quite environmentally friendly and reliable, although among car owners and repair professionals are considered "capricious".
Practical application in the motor industry
In the 70s and 80s, some manufacturers of motorcycles were experimed with RPD - Hercules, Suzuki and others. Currently, the petrolery production of "rotary" motorcycles has been established only in the Norton company, which produces the NRV588 model and the NRV700 motorcycle prepare for serial production.
Norton NRV588 - Sportbike, equipped with a two-engine engine with a total volume of 588 cubic centimeters and developing power in 170 horse power. With a dry weight of a motorcycle in 130 kg, the energy-fitness of the sportsbike looks literally to be processed. The engine of this machine is equipped with the inlet path systems of the variable and electronic fuel injection. About the model NRV700 It is only known that the power of the RPD of this sportbike will reach 210 hp.
Piston DVSs found the wider distribution as energy sources on automobile, railway and sea transport, in agricultural and construction industries (tractors, bulldozers), in emergency energy systems of special objects (hospitals, communication lines, etc.) and in many others regions of human activity. In recent years, mini-CHP based on gas pipelines, with the help of which the tasks of the energy supply of small residential areas or industries are effectively solved. The independence of such CHPs from centralized systems (type RAO UES) improves the reliability and stability of their functioning.
Extremely diverse piston engineers are capable of providing a very wide capacity interval - from very small (engine for aircraft models) to very large (engine for ocean tankers).
With the basics of the device and the principle of the actions of the piston DVS, we have repeatedly acquainted, ranging from the school course of physics and ending with the course "Technical thermodynamics". And yet, to secure and deepen the knowledge, consider it very briefly once again this question.
In fig. 6.1 shows the engine device diagram. As you know, burning fuel in the engine is carried out directly in the working body. In piston engine, such burning is carried out in the working cylinder 1 with the piston moving in it 6. The flue gases resulting as a result of combustion pushed the piston, forcing it to make a useful work. The progressive movement of the piston with a connecting roddle 7 and the crankshaft 9 is converted into a rotational, more convenient for use. The crankshaft is located in the crankcase, and the engine cylinders - in another case part, called a block (or shirt) of cylinders 2. In the cylinder lid 5 are intake 3 and graduation 4 Valves with a forced cam drive from a special distributor, kinematically associated with a crankshaft machine.
Fig. 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 oxidizing agent (air), which is carried out due to the movements of the piston and valve operation.
Piston DVS is customary to classify according to various general features.
- 1. According to the method of mixing, ignition and heat supply, the engines are divided into machines with forced ignition and with self-ignition (carburetor or injection and diesel).
- 2. On the organization of the workflow - on four-stroke and two-strokes. In the last workflow, the workflow is made not for four, and for the two stroke of the piston. In turn, the two-stroke engine is divided into machines with a straight-flow valve-slit purge, with a crank-chamber blowing, with a straight-flow purge and oppositely moving pistons, etc.
- 3. For its intended purpose - to stationary, ship, diesel, automotive, autotractor, etc.
- 4. In terms of speed - on low-speed (up to 200 rpm) and high-speed.
- 5. P. mid speed Piston y\u003e n \u003d? p / 30 - on low-speed and high-speed (s? "\u003e 9 m / s).
- 6. According to the pressure of the air at the beginning of the compression - on ordinary and superimposed using drive blowers.
- 7. On the use of heat exhaust gases - On ordinary (without using this heat), with turbocharging and combined. Cars with turbocharged exhaust valves There are several earlier conventional and flue gases with higher pressure, which is usually directed to a pulsed turbine, which drives the turbocharger supplying air to the cylinders. This allows you to burn more fuel in the cylinder, improving and efficiency, and specifications cars. In combined internal combustion engine, the piston part serves in a large gas generator and produces only ~ 50-60% of the machine power. The rest of the total capacity is obtained from a gas turbine operating on flue gases. For this flue gases at high pressure r And temperature / are directed to the turbine, the shaft of which, using a toothed transmission or hydromeflua, transmits the obtained power of the main set of installation.
- 8. In terms of the number and location of cylinders, the engines are: single, two- and multi-cylinder, row, k-shaped ,.t-shaped.
We now consider the real process of a modern four-stroke diesel. Four-stroke it is called because full cycle Here is carried out for four full piston stroke, although we will see now, during this time there are several more real thermodynamic processes. These processes are clearly represented in Fig. 6.2.
Fig. 6.2.
I - suction; II - compression; III - work move; IV - Poverty
During takta suction (1) Suction (intake) The valve opens in several degrees to the top of the dead point (VTT). The point of opening corresponds to the point g. on the r- ^ -Diagram. In this case, the suction process occurs when the piston moves to the lower dead point (NMT) and goes for pressure r NS. less atmospheric /; A (or pressurization pressure r). With a change in the direction of the movement of the piston (from NMT to NTC), the intake valve is also not immediately closed, but with a certain delay (at the point t.). Next, with the valves closed, the working fluorescence is compressed (to the point from). IN diesel cars Clean air is absorbed and compressed, and in carburetor - a working mixture of air with gasoline pairs. This piston move is customary to call compression (Ii).
In a few degrees, the angle of rotation of the crankshaft to the VMT into the cylinder is injected through the nozzle diesel fuelIt occurs its self-ignition, combustion and expansion of combustion products. IN carburetor machines The working mixture is enforced by the electrical spark discharge.
When compressing air and a relatively small heat exchange with walls, its temperature is significantly increased, exceeding the temperature of self-ignition fuel. Therefore, injected finely sprayed fuel warms very quickly, evaporates and lights up. As a result of the combustion of the fuel, the pressure in the cylinder first sharply, and then, when the piston starts its way to NMT, with a decreasing pace increases to a maximum, and then as the last portions of the fuel arrived during the injection, even begins to decrease (due to intensive growth cylinder volume). We will consider conditionally that at the point from" The burning process ends. Next, the process of expanding flue gases is followed, when the power of their pressure moves the piston to NMT. The third stroke of the piston, including the processes of combustion and expansion, is called workforce (Iii), for only at this time the engine makes a useful work. This work accumulate with the help of the flywheel and give to the consumer. Part of the accumulated work is consumed when performing the other three clocks.
When the piston is approaching NMT, the exhaust valve opens with some advance (point B) and spent flue gases rushed into exhaust pipeAnd the pressure in the cylinder drops sharply almost to atmospheric. During the piston, the flue gases from the cylinder occurs from the cylinder (IV - pushing). 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 later the passage of the NTT (point p),gAK that in each cycle there is a situation where both intake and exhaust valves are both open and the exhaust valve (they say about the overlap of valves). This allows you to better clean the working cylinder from the combustion products, the effectiveness and completeness of the combustion of fuel increases as a result.
A different cycle of two-stroke machines is organized (Fig. 6.3). Usually these are supervised engines, and for this they, as a rule, have a drive blower or turbocharger 2 which drums the air into the air receiver during operation 8.
The two-stroke engine cylinder always has purge windows 9, through which air from the receiver enters the cylinder when the piston, passing to the NCT, will start opening them more and more.
For the first stroke of the piston, which is customary to be called a workforce, in the cylinder of the engine is combustion of injected fuel and expansion of combustion products. These processes on the indicator diagram (Fig. 6.3, but) Reflected Liniya c - I - t. At point t.exhaust valves open and under the action of overpressure, flue gases are rushed into the graduation path 6, in the result
Fig. 6.3.
1 - suction nozzle; 2 - blower (or turbocharger); 3 - piston; 4 - exhaust valves; 5 - nozzle; 6 - graduation tract; 7 - worker
cylinder; 8 - air receiver; 9- blowing windows
tATE The pressure in the cylinder falls noticeably (point p). When the piston descends so much that the purge windows begin to open, compressed air from the receiver rushes into the cylinder 8 , pushing out the remains of flue gases from the cylinder. In this case, the working volume continues to increase, and the pressure in the cylinder decreases almost to the pressure in the receiver.
When the direction of the piston movement changes to the opposite, the process of purging the cylinder continues until the blowing windows remain at least partially open. At point to(Fig. 6.3, b) The piston completely overlaps the blowing windows and the compression of the next portion of the air that has fallen into the cylinder begins. In a few degrees to VTT (at the point from") The fuel injection begins through the nozzle, and then the previously described processes leading to ignition and fuel combustion.
In fig. 6.4 Schemes explaining the structural device of other types of two-stroke engines. In general, the working cycle in all these machines is similar to the described, and constructive features largely affect only duration
Fig. 6.4.
but - looped slit purge; 6 - Direct-time purge with oppositely moving pistons; in - crank-chamber purge
individual processes and, as a result, at the technical and economic characteristics of the engine.
In conclusion, it should be noted that two-stroke engines Theoretically allowed, in other things being equal, to get twice as high capacity, but in reality due to the worst conditions for cleaning the cylinder and relatively large internal losses, this win is somewhat less.
