(by 20-45%) without increasing the mass and dimensions of the engine, as well as to compensate for the drop in power in high altitude conditions. Supercharging with "quality control" can be used to reduce the toxicity and smoke of the exhaust gases. Aggregate supercharging is carried out using a compressor, turbocharger or in combination. The most widespread is supercharging with the help of a turbocharger, for the drive of which the energy of the exhaust gases is used.

Aggregate supercharging is used in almost all types of transport diesel engines (ship, diesel, tractor). Aspiration on carbureted engines is limited by the occurrence of knocking. The main disadvantages of aggregate supercharging include:

  • an increase in the mechanical and thermal stress of the engine due to an increase in the pressure and temperature of the gases;
  • decrease in efficiency;
  • complication of the design.

Aggregate-free supercharging includes:

  • dynamic (previously called inertial, resonant, acoustic), in which the effect is achieved due to oscillatory phenomena in pipelines;
  • high-speed, used on piston aircraft engines at heights higher than the calculated one and at speeds over 500 km / h;
  • refrigeration, achieved by evaporation of fuel or any other flammable liquid with a low boiling point and high heat of vaporization in the incoming air.

Dynamic pressurization is becoming more and more widespread in transport internal combustion engines, which, with insignificant changes in the design of the pipelines, leads to an increase in the filling factor up to a wide range of changes in the engine speed. The boost during boost makes it possible to boost the diesel in terms of energy indicators in the event of a simultaneous increase in the cyclic fuel supply, or to improve economic indicators while maintaining power (with the same cyclic fuel supply). Dynamic pressurization increases the durability of parts of the cylinder-piston group due to lower thermal conditions when working on lean mixtures.

see also

Links

  • Turbocharger versus mechanical compressor

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See what "Aspiration" is in other dictionaries:

    1) an increase in the amount of fresh charge of the combustible mixture in the cylinder of a piston engine due to an increase in the inlet pressure; one of the ways to increase engine power. 2) Artificial increase of gas pressure in an enclosed space (for example, in ... Big Encyclopedic Dictionary

    Additional, against normal, supply of air (or a combustible mixture) to the engine cylinder, compressed to 1.1 1.3 atm by means of a pump driven from the engine shaft or from an external energy source. It is used to improve ... ... Marine vocabulary

    - - the way of feeding the fuel into the combustion chamber. EdwART. Automotive Jargon Dictionary, 2009 ... Automotive Dictionary

    pressurization- - [A.S. Goldberg. The English Russian Energy Dictionary. 2006] Topics energy in general EN supercharging ... Technical translator's guide

    BLOWER- (1) a method for increasing the power of reciprocating internal combustion engines by increasing the mass of air entering the cylinders together with the fuel due to the increase in pressure by the compressor at the inlet; (2) artificial increase in gas pressure in ... ... Big Polytechnic Encyclopedia

    pressurization- 3.13 pressurization: Provision of protection against the penetration of the external environment into the enclosure by maintaining the pressure of the protective gas in it above the pressure in the external environment. Source: GOST R 51330.3 99: Electrical equipment for explosion ... Dictionary-reference book of terms of normative and technical documentation

    A; m. Special. Strengthening the supply of the combustible mixture to the internal combustion engine by increasing the air pressure at the intake. Supercharged engine. * * * supercharging 1) increasing the amount of fresh charge of the combustible mixture supplied to the piston cylinder ... ... encyclopedic Dictionary

    pressurization- oro įpūtimas statusas T sritis Energetika apibrėžtis Į vidaus degimo variklį tiekiamo degiojo mišinio kiekio didinimas, didinant šio mišinio slėgį. atitikmenys: angl. air blast vok. Lufteinblasen, n rus. blowing air, n; boost, m pranc. ... ... Aiškinamasis šiluminės ir branduolinės technikos terminų žodynas

    Increasing the amount of fresh charge of the combustible mixture supplied to the Internal Combustion Engine by increasing the intake pressure. N. is usually used to increase power (by 20 to 45%) without increasing weight and dimensions ... ... Great Soviet Encyclopedia

    M. Power supply of cylinders of piston engines of the machine with air, the pressure of which is higher than atmospheric. Efremova's Explanatory Dictionary. T.F. Efremova. 2000 ... Modern explanatory dictionary of the Russian language by Efremova

Boosting allows an increase in engine power by increasing the air density at the inlet to the cylinders, which makes it possible to efficiently burn more fuel. In the engines of automotive vehicles, gas turbine pressurization systems are used using turbochargers (TKR) or mechanical pressurization using drive blowers (PN). In the TKR, air is compressed by a compressor driven by a turbine, and the turbine is rotated by the flow of exhaust gases (see Fig. 7.22). PN, compressing air, is driven from the engine crankshaft.

The turbocharger of a motor vehicle engine (Fig. 7.26) is a unit consisting of a housing and a rotor (turbine and compressor, united by a shaft rotating in sleeve bearings). TKR may contain controls for its operation. Typically, the outer diameter of the wheels of centrifugal compressors and radial-axial turbines TKR 35 ... 90 mm, which provides a fairly high efficiency. The compressor wheels are made of aluminum alloy and the turbine wheels are made of high alloy cast iron, as they have to withstand high temperatures. Exhaust gas enters the turbine scroll casing 6. It contains one or two tapering guide channels in which the exhaust gas velocity increases. Then they are fed to the blades of the turbine wheel 7, causing it to rotate. She's through the shaft 11 drives the compressor wheel 2. Air through the compressor inlet 1 enters the inlet to the compressor wheel 2 , where, under the action of centrifugal forces, its speed increases sharply, and leaves the wheel into the diffuser, where its speed decreases and the density increases. Then the air 4 enters the spiral collector of the compressor housing, from where it is sent to the engine.

Rice. 7.26.

1 - compressor housing; 2 - compressor wheel; 3 - air inlet; 4 - outlet of air compressed in the compressor; 5 - oil supply; 6 - turbine housing; 7- turbine wheel; 8- exhaust gas outlet after turbine; 9- bearing housing; 10- exhaust gas inlet from the engine; 11 - rotor shaft; 12 - oil drain

A Rute-type drive blower in the form of two eight-shaped rotors connected by gears, rotating in different directions, is shown in Fig. 7.27. Rotors alternately approach the upper edges of the housing and capture the volume of air V, at atmospheric pressure p 0. This amount of air, practically without changing the pressure, is pushed into the outlet chamber of the PN, where there is a charge with increased pressure p k. When reporting volume V with the outlet chamber, the existing charge enters it under pressure p k. The seal between the rotors and between the rotors and the casing walls is achieved by creating a minimum clearance. At high boost pressures at high speeds, leaks become significant, which reduces the pressure rise and the efficiency of the supercharger. Therefore, the maximum degree of pressure increase in such a supercharger does not exceed 1.6 ... 1.7.

Comparison of a turbocharger and a driven supercharger. TKR is much more widely used for pressurizing automotive vehicles than PN, since it provides a higher boost pressure and better efficiency, lower noise level, and lighter weight and dimensions.

Rice. 7.27.

The worst efficiency of the PN, in contrast to the TCR, driven by the energy of the exhaust gases, is due to the fact that the PN operates from the crankshaft. Being rigidly connected to the crankshaft, the PN provides a higher boost pressure at low rotational speeds and, in contrast to the TKR, does not have a delay in the spinning of the rotor with a sharp increase in the engine load ("turbo lags"). This ensures the best dynamics of vehicles with PN, especially in the initial phase of acceleration. At low loads, the power to the drive of the PN does not decrease, which makes the use of the PN especially unprofitable. PN, switched off at low loads and high speeds, is usually used on gasoline engines of passenger cars, for which acceleration dynamics is important, and the deterioration of efficiency is not of great importance.

Charge air coolers (CAC). For engines of automotive vehicles, when air is compressed in a compressor, the temperature rise is usually 40 ... 180 ° C. When the air is intercooled in the CAC, the mass filling of the cylinders increases due to the increase in the air density, which provides an increase in the power and improvement of the engine's economy. The use of NVG also reduces the temperature of engine parts and the temperature of gases in front of the turbine.

Air-to-air and liquid-air NVG are used on the engines of automotive vehicles. In the first case, the charge air is cooled due to the blowing of the CAC by the flow of oncoming air when the vehicle is moving and by the flow generated by the fan, and in the second, the liquid from the engine cooling system is mainly used.

Liquid-air NVG is more compact than air-to-air. This is due to the fact that heat exchange from hot air to the coolant occurs more intensively than to the cooling air. This heat exchanger ensures a stable charge air temperature regardless of the ambient temperature. It is mainly installed on cross-country vehicles, tractors and special vehicles (mining dump trucks, airfield equipment, etc.).

Air-to-airОН В provides deeper cooling due to the fact that the temperature of the ambient air is lower than the temperature of the liquid in the cooling system. Therefore, it is used at low degrees of boost boost and in the presence of oncoming air flow, which applies to engines of cars and mainline trucks.

Boost control systems. With an increase in the engine speed, the TKP boost pressure increases by 1.3 ... 1.5 times. This is due to the difference in hydraulic characteristics of piston (engine) and blade (TKR) machines. Ideally, the TKR can be configured for only one mode of engine operation (usually this is the point of the external speed characteristic located between the modes of maximum torque and rated power), at which it will provide the specified boost pressure and have the highest efficiency. Then, with a decrease in the speed of rotation, the boost pressure will fall in relation to the optimal one, and with an increase in the speed, it will increase. To solve these problems, various methods of boost control are used on engines.

Exhaust gas bypass, bypassing the turbine, is the simplest way of coordinating the operation of the engine and TCR (Fig. 7.28). TKP is adjusted to ensure high boost pressure at low and medium engine speeds, and at high engine speeds, further pressure growth is limited by opening the bypass valve 5. It is installed at the turbine inlet. 8. When it is opened, part of the gas is directed, bypassing the turbine, into the exhaust system. The engine management system regulates the amount of valve opening to provide the required boost pressure in each mode of operation. However, when the bypass valve is open, the economy of the engine decreases, since part of the energy spent on compressing the air in the TKR compressor is lost.

Changing the flow area by rotating blades at the exhaust gas inlet to the turbine wheel. At low rotational speed, the rotary blades 3 at the turbine inlet 1 at low speed (fig. 7.29, a) rotated to the maximum angle, providing a minimum flow area at the exhaust gas inlet to the turbine wheel 1. Then the speed of the gas at the entrance to the wheel will increase, which increases the rotational speed of the TKR rotor.

Rice. 7.28.

  • 1 - solenoid valve; 2 - Vacuum pump; 3 - vacuum chamber; 4 - TKR; 5 - OT bypass valve; 6 - OT input from the engine;
  • 7 - compressed air outlet; 8 - turbine; 9 - compressor

and, accordingly, the boost pressure. At a high engine speed (Fig. 7.29, b) shoulder blades 3 rotated to the minimum angle, providing the maximum flow area at the exhaust gas inlet to the turbine wheel 1. Then the speed of the gas at the entrance to the turbine wheel is reduced, which prevents an increase in the boost pressure. At the same time, the back pressure at the outlet from the cylinders decreases, which leads to a decrease in the ejection work and, as a result, to an increase in the power and economy of the diesel engine. With this method of regulation on small TKP, the efficiency of the turbine is significantly reduced due to an increase in the resistance created by the blades on the path of the gas flow, and losses associated with leaks through the gaps between the blades and the walls of the turbine housing. There are also difficulties in ensuring the operability of the rotary blades in the conditions of soot deposition. Therefore, TKP with this method of regulation are used on engines of passenger cars with a working volume of more than two liters.

Changing the flow area for supplying О Гк to the turbine wheel with a sliding sleeve in the turbine nozzle guide van. In TKR (Fig. 7.30), a horizontally moving sliding sleeve can close one of two channels located in the turbine housing and supplying OT to its wheel. This changes the flow area and, accordingly, the speed of gas entry into the turbine blades. If open

Rice. 7.29. Regulation of the TKR turbine by turning the blades: a- the closed position of the blades, the minimum flow area and the maximum speed of gas inlet to the turbine wheel; b- the open position of the blades, the maximum flow area and the minimum speed of gas inlet to the turbine wheel; 1 - turbine wheel;

2 - swivel ring; 3 - swivel blade; 4 - drive lever; 5 - pneumatic regulator; 6 - Exhaust gas flow only one channel 2 (fig. 7.30, a), the cross-section on the path of the gas flow is minimal, the gas velocity is maximal, and the boost pressure increases. If both channels are open 2 and 3 (fig. 7.30, b), then the flow area is maximum, and the gas velocity is minimum. In this case, the boost pressure decreases and the exhaust back pressure from the cylinders decreases. This control method allows the use of TKR with small wheel diameters, which can be used on small displacement engines.

Rice. 7.30. Regulation of the turbine TKP with a sliding sleeve: a- only one gas supply channel in the turbine housing is open; b- both channels supplying gases in the turbine housing are open; 1 - turbine wheel; 2 - the first channel in the turbine housing; 3 - the second channel in the turbine housing; 4 - sliding sleeve; 5 - bypass channel; 6 - sliding sleeve drive

Mechanical supercharging is one of the ways to increase engine power. The main element of such a system is a mechanical supercharger (Supercharger or compressor). It is a compressor driven by rotation of the crankshaft. Installing a mechanical blower provides an increase of up to 50%. The Supercharger draws in air through the air filter, compresses and then sends it to the intake manifold of the internal combustion engine, which contributes to the increase in the power of the latter.

The design and principle of operation of mechanical pressurization

In the modern automotive industry, several types of mechanical pressurization systems are used, each of which has its own design features and the principle of air injection.

Mechanical pressurization device

The mechanical pressurization system consists of the following elements:

  • mechanical blower (compressor);
  • intercooler;
  • throttle valve;
  • bypass damper;
  • air filter;
  • boost pressure sensors;
  • intake manifold air temperature sensors.
Mechanical pressurization scheme

The mechanical supercharger is controlled by the throttle valve, which is open at high speeds. In this case, the valve of the pipeline is closed, and all the air enters the intake manifold of the engine. When the engine is running at low rpm, it is open at a slight angle and the pipeline damper is fully open, which allows some of the air to return to the compressor inlet.

The air coming from the supercharger flows through the intercooler, which lowers the discharge air temperature by about 10 ° C, contributing to a higher compression ratio.

Mechanical pressurization drive types


 Cam compressor belt drive

The transmission of torque from the crankshaft to the mechanical compressor can be done in different ways:

  • Direct Drive System - This involves mounting the compressor directly to the engine crankshaft flange.
  • Belt drive. The transmission of forces is carried out using a belt. Different manufacturers use different types of belts (flat, V-shaped or toothed). Belt systems are characterized by short lifespan and slippage potential.
  • Chain drive. It has a principle similar to a belt drive.
  • Gear drive. The disadvantage of such a system is the increased noise and large dimensions.

Types of mechanical compressors

Centrifugal compressor

Each type of boost drive has its own operational characteristics. In total, there are three types of mechanical blowers:

  • Centrifugal blower. The most common type of mechanical blower. The main working element of the system is a wheel (impeller), which has a similar design to a compressor wheel. It rotates at a speed of about 60,000 rpm. In this case, air is sucked into the central part of the compressor wheel at high speed and low pressure. Having passed through the blades of the supercharger, air is supplied to the intake manifold, but already at low speed and high pressure. This type of supercharger is used in conjunction with turbochargers for elimination.
  • Screw blower. It is a system of two rotating conical screws (screws). Air entering the wider part passes through the compressor chambers and, due to rotation, is compressed and forced into the intake manifold. Such systems are used mainly in sports and expensive cars, since they are rather complicated to manufacture. Their advantage is high work efficiency.
  • Roots cam blower. One of the first types of mechanical blowers. Structurally, it consists of two rotors with a complex cross-sectional profile. The axes of rotation of the rotors are connected by two identical gears. When the system rotates, air moves between the walls of the housing and the cams, as a result of which it is forced into the intake manifold. The disadvantage of this system is the formation of excess pressure, which provokes malfunctions in the work of the pressurization. To eliminate this phenomenon, the design of the cam supercharger provides either an electrically driven clutch (control with shutdown of the supercharger), or a bypass valve (without shutdown of the supercharger).

 Screw blower

Mechanical superchargers are quite often used on cars of the Cadillac, Audi, Mercedes-Benz and Toyota brands. At the same time, cam and screw compressors are installed mainly on powerful sports cars with gasoline engines, and centrifugal ones are part of the dual turbocharging system for diesel engines.

Advantages and disadvantages of a mechanical supercharger circuit

Compared to a turbocharger, the mechanical charging system is not driven by the exhaust gases of the engine, but by the rotation of the crankshaft. This means that, on the one hand, the motor power increases, and on the other hand, an additional load arises, which, depending on the type of compressor, takes up to 30% of the engine performance. Also the disadvantage of the system is the high noise level that the system drive creates.

The use of mechanical supercharging at higher speeds provokes faster wear of engine parts, and therefore they must be made of materials of increased strength.
The main advantage of the mechanical drive is the low manufacturing cost (compared to turbocharging), ease of installation, as well as the immediate response of the system to an increase in engine speed. So systems with screw and cam compressors provide high acceleration dynamics, and centrifugal blowers ensure stable engine operation at high speeds.

In addition to being driven by the engine's crankshaft, the mechanical boost can be powered by a separate electric motor. In this case, loss of motor power is avoided.

The task of increasing the power and torque of the engine has always been relevant. Engine power is directly related to the working volume of the cylinders and the amount of fuel-air mixture supplied to them. That is, the more fuel burns in the cylinders, the more power the power unit develops. However, the simplest solution is to increase the engine power by increasing its working volume, which leads to an increase in the dimensions and weight of the structure.

The amount of the supplied working mixture can be increased by increasing the revolutions of the crankshaft (in other words, to realize a greater number of working cycles in the cylinders per unit of time), but this will cause serious problems associated with an increase in inertial forces and a sharp increase in mechanical loads on the parts of the power unit, which will lead to a decrease in the resource of the motor. The most effective way in this situation is to pressurize.

Imagine the intake stroke of an internal combustion engine: the engine at this time works as a pump, moreover, it is very ineffective - there is an air filter in the air path, the bends of the intake ducts, in gasoline engines there is also a throttle valve. All this will certainly reduce the filling of the cylinder. Well, what is required to raise it? Raise the pressure in front of the inlet valve - then more air will “fit” in the cylinder. When supercharged, the filling of the cylinders with a fresh charge improves, which makes it possible to burn more fuel in the cylinders and thereby obtain a higher aggregate engine power.

Three types of pressurization are used in internal combustion engines:

  • resonant - in which the kinetic energy of the air volume in the intake manifolds is used (a supercharger is not needed in this case)
  • mechanical - in this version the compressor is driven by a belt from the engine
  • gas turbine (or turbocharging) - the turbine is driven by the flow of exhaust gases.

Each method has its own advantages and disadvantages, which determine the field of application.

As noted at the beginning of the article, for better filling of the cylinder, the pressure should be raised in front of the intake valve. Meanwhile, the increased pressure is not necessary at all constantly - it is enough for it to rise at the moment of closing the valve and "load" the cylinder with an additional portion of air. For a short-term increase in pressure, a compression wave is quite suitable, "walking" along the inlet pipeline when the engine is running. It is enough just to calculate the length of the pipeline itself so that the wave, reflected several times from its ends, comes to the valve at the right moment.

The theory is simple, but its implementation requires a lot of ingenuity: the valve is open at different crankshaft speeds for different times, and therefore, to use the effect of resonant boost, intake pipes of variable length are required. With a short intake manifold, the engine runs better at high rpm, while at low rpm, a long intake tract is more efficient. Variable inlet pipe lengths can be created in two ways: either by connecting a resonance chamber, or by switching to the desired inlet or connecting it. The latter option is also called dynamic supercharging. Both resonant and dynamic charging can accelerate the flow of the intake air column.

The pressurization effects created by fluctuations in the air flow head range from 5 to 20 millibars. By comparison, with turbo or mechanical charging, values ​​between 750 and 1200 millibars can be obtained. For the sake of completeness, we note that there is also inertial boost, in which the main factor in creating excess pressure in front of the valve is the velocity head of the flow in the intake manifold. Gives a slight increase in power at high (over 140 km / h) travel speeds. Mainly used on motorcycles.

Mechanical superchargers (in English supercharger) allow a fairly simple way to significantly increase the power of the engine.
Having a drive directly from the engine crankshaft, the compressor is able to pump air into the cylinders at minimum speed without delay to increase the boost pressure in strict proportion to the engine speed. But they also have disadvantages. They reduce the efficiency of the internal combustion engine, since their drive consumes part of the power generated by the power unit. Mechanical pressurization systems take up more space, require a special drive (toothed belt or gear drive) and generate a lot of noise.


There are two types of mechanical blowers: positive displacement and centrifugal.

Typical positive displacement blowers are the Roots blower and the Lysholm compressor.

The Roots design resembles an oil gear pump. The two rotors rotate in opposite directions inside the oval body. The rotor axles are interconnected by gears. The peculiarity of this design is that the air is not compressed in the supercharger, but outside - in the pipeline, falling into the space between the casing and the rotors. The main disadvantage is the limited boost value. No matter how flawlessly fit the parts of the blower, when a certain pressure is reached, air begins to leak back, reducing the efficiency of the system. There are few ways to fight: increase the rotational speed of the rotors or make the supercharger two- or even three-stage.

Thus, it is possible to increase the final values ​​to an acceptable level, however, multistage structures are deprived of their main advantage - compactness. Another disadvantage is the uneven discharge at the outlet, because the air is supplied in portions. In modern designs, three-tooth rotors of a spiral shape are used, and the inlet and outlet ports are triangular in shape. Thanks to these tricks, the positive displacement blowers practically got rid of the pulsating effect. Low rotor speeds, and, consequently, the durability of the structure, coupled with low noise, have led to the fact that such famous brands as DaimlerChrysler, Ford and General Motors are generously equipped with them.

Displacement superchargers raise power and torque curves without changing their shape. They are already effective at low and medium revs, and this has the best effect on the acceleration dynamics. The only problem is that such systems are very whimsical to manufacture and install, which means they are quite expensive.

Another way to inject air into the intake manifold under excess pressure was once proposed by engineer Lysholm. His brainchild was dubbed the screw supercharger, or "double screw" (double screw). The Lysholm pressurization design is somewhat reminiscent of an ordinary meat grinder.
Two complementary screw pumps (auger) are installed inside the housing. Rotating in different directions, they capture a portion of air, squeeze and drive it into the cylinders. This system is characterized by internal compression and minimal losses, thanks to precisely adjusted clearances.
In addition, screw superchargers are efficient in almost the entire engine speed range, are silent, very compact, but extremely expensive due to the complexity of manufacturing. However, they do not disdain such eminent tuning studios as AMG or Kleemann.

Centrifugal superchargers are similar in design to turbocharging. Excessive pressure in the intake manifold also creates a compressor wheel (impeller). Its radial blades capture and propel air into the circumferential tunnel using centrifugal force. The difference from turbocharging is only in the drive. Centrifugal blowers suffer from a similar, albeit less noticeable inertial defect, but there is another important feature. In fact, the amount of pressure produced is proportional to the square of the compressor wheel speed.

Simply put, it must rotate very quickly in order to inflate the necessary air charge into the cylinders, sometimes tens of times higher than the engine speed. A centrifugal blower at high speeds is effective. Mechanical "centrifuges" are not so capricious in maintenance and more durable than gas-dynamic counterparts, since they operate at less extreme temperatures. Unpretentiousness, and, consequently, the cheapness of the design won them popularity in the field of amateur tuning.

The control circuit for a mechanical supercharger is quite simple. At full load, the bypass valve is closed and the throttle valve is open - all air flow enters the engine. In partial load operation, the throttle valve closes and the line valve opens - excess air is returned to the blower inlet. The intercooler included in the circuit is an almost indispensable part of not only mechanical, but also gas turbine pressurization systems.

When compressed in a compressor (or in a supercharger), the air heats up, as a result of which its density decreases. This leads to the fact that in the working volume of the cylinder, air, and, consequently, oxygen, is placed in mass less than it could fit in the absence of heating. Therefore, the compressed air is pre-cooled in an intercooler before being fed into the engine cylinders. By its design, this is a conventional radiator, which is cooled either by the flow of incoming air or by a cooling liquid. Lowering the charge air temperature by 10 degrees allows it to increase its density by about 3%. This, in turn, allows the engine power to be increased by about the same percentage.

Gas turbine supercharging

More widely, turbochargers are used on modern automobile engines. In fact, this is the same centrifugal compressor, but with a different drive circuit. This is the most important, one might say, the fundamental difference between mechanical and turbo superchargers. It is the drive circuit that largely determines the characteristics and areas of application of certain designs. In a turbocharger, the supercharger impeller sits on the same shaft with the turbine impeller, which is built into the engine exhaust manifold and is driven by exhaust gases. The rotational speed can exceed 200,000 rpm. There is no direct connection with the engine crankshaft, and the air supply is controlled by the exhaust gas pressure.

The advantages of turbocharging include: increasing the efficiency and economy of the engine (the mechanical drive takes power from the engine, the same one uses the energy of the exhaust gases, therefore, increases the efficiency). The specific and general efficiency of the motor should not be confused. Naturally, for the operation of an engine, the power of which has increased due to the use of turbocharging, more fuel is required than for a similar naturally aspirated engine of lower power. After all, filling the cylinders with air is improved, as we remember, in order to burn more fuel in them. But the mass fraction of fuel per unit of power per hour for an engine equipped with a TC is always lower than that of a power unit of a similar design, devoid of pressurization.

Turbocharging makes it possible to achieve the specified characteristics of the power unit with smaller dimensions and weight than in the case of using an "atmospheric" engine. In addition, the turbo engine has better environmental performance. The pressurization of the combustion chamber results in a decrease in temperature and, therefore, in a decrease in the formation of nitrogen oxides. In supercharged gasoline engines, more complete fuel combustion is achieved, especially in transient operating modes. In diesel engines, the additional air supply allows you to push the border of the occurrence of smoke, that is, to combat the emission of soot particles.

Diesel engines are much better adapted to supercharging in general, and to turbocharging in particular. Unlike gasoline engines, in which the boost pressure is limited by the danger of detonation, they are not aware of this phenomenon. Diesel can be pressurized until the maximum mechanical loads in its mechanisms are reached. In addition, the lack of throttling of the intake air and the high compression ratio provide higher exhaust gas pressure and lower temperature in comparison with gasoline engines. In general, just what you need for a turbocharger application. Turbochargers are easier to manufacture, which compensates for a number of inherent disadvantages.

At a low engine speed, the amount of exhaust gases is small, therefore, the compressor efficiency is low. In addition, a turbocharged engine usually has a so-called. "Turbo-lag" (in English "turbo-lag") - a slower response to an increase in fuel supply. You need to accelerate sharply - press the gas pedal to the floor, and the engine “thinks” for a while and only then picks up. The explanation is simple - it takes time until the engine picks up speed, the exhaust gas pressure rises, the turbine spins up, the supercharger impeller goes along with it - and finally, the air will “go”. The designers are trying to get rid of these shortcomings in different ways. First of all, by reducing the mass of the rotating parts of the turbine and compressor. The rotor of a modern turbocharger is so small that it fits easily in the palm of your hand.

Weight reduction is achieved not only by the design of the rotor, but also by the selection of appropriate materials for it. The main difficulty in this is the high temperature of the exhaust gases. The sintered rotor of the turbine is about 20% lighter than the one made of heat-resistant alloys, and besides, it has a lower moment of inertia. Until recently, the service life of the entire unit was limited by the service life of the bearings. Essentially, they were crankshaft-like liners that were lubricated with oil under pressure. The wear of such plain bearings was, of course, great, but the ball bearings could not withstand the enormous rotational speed and high temperatures. The solution was found when it was possible to develop bearings with ceramic balls. However, the use of ceramics is not surprising - the bearings are filled with a constant supply of grease, that is, the channel from the standard engine oil system is no longer needed!

To get rid of the disadvantages of a turbocharger allows not only a decrease in the inertia of the rotor, but also the use of additional, sometimes rather complex, boost pressure control schemes. The main tasks in this case are to reduce the pressure at high engine speeds and increase it at low ones. All problems can be completely solved by using a turbine with a variable geometry (Variable Nozzle Turbine), for example, with movable (rotary) blades, the parameters of which can be changed within wide limits.

The principle of operation of a VNT turbocharger is to optimize the flow of exhaust gases directed to the turbine impeller. At low engine speeds and low exhaust gases, the VNT turbocharger directs the entire exhaust gas flow to the turbine wheel, thereby increasing its power and boost pressure. At high rpm and high gas flow, the VNT turbocharger positions the movable blades in the open position, increasing the cross-sectional area and diverting some of the exhaust gases from the impeller, protecting itself from overspeeding and maintaining the boost pressure at the required engine level, eliminating overcharging.

Combined systems

In addition to single pressurization systems, two-stage pressurization is now common. The first stage - the drive compressor - provides effective boost at low engine speeds, and the second - the turbocharger - utilizes the energy of the exhaust gases. After the power unit reaches the rpm sufficient for normal operation of the turbine, the compressor automatically turns off, and when they fall, it re-enters into action.

A number of manufacturers install two turbochargers on their motors at once. Such systems are called "biturbo" or "twin-turbo". There is no fundamental difference in them, with only one exception. "Biturbo" implies the use of turbines of different diameters and, therefore, performance. Moreover, the algorithm for their inclusion can be both parallel and sequential (sequential). At low revs, a small diameter turbocharger quickly spins up and starts to work, at medium revs the "big brother" is connected to it.

Thus, the acceleration characteristic of the car is leveled. The system is expensive and can be found on prestigious vehicles like Maserati or Aston Martin. The main task of the "twin-turbo" is not to smooth out the "turbo lag", but to achieve maximum performance. In this case, two identical turbines are used. Installed "twin" and "biturbo" both on V-shaped blocks and in-line motors. The turbine connection options are also identical to the biturbo system. What's the point? The fact is that the performance of a turbine directly depends on two of its parameters: diameter and rotation speed. Both indicators are quite capricious. An increase in diameter leads to an increase in inertia and, as a consequence, to the notorious "turbo lag". The speed of the turbine is limited by the permissible loads on the materials. Therefore, two modest and less inertial turbines can be more efficient than one large one.

First, change the oil and oil filter in time. Second, use only turbocharged engine oil that is originally designed for higher temperatures than normal. But on the road anything can happen, and if you had to fill in an unknown oil, then do not drive, move slowly. The engine will survive this oil, but turbocharging is not necessary. When you arrive home, change the oil and oil filter immediately.

And finally, the third, the most important condition for the normal operation of the turbocharger. There are two most crucial moments in the life of a turbine: starting the engine and stopping it. When starting a cold engine, the oil in it has a high viscosity, it is hardly pumped through the clearances; thermal gaps have not yet been established; the heating of different parts of the compressor, and therefore the thermal expansion, go at different rates. So take your time, let the engine warm up.

If you have to stop, never turn off the engine right away. Depending on the driving mode, let it idle for 2-5 minutes (longer in winter). During this time, the turbine shaft will reduce the speed to the minimum, and the parts in direct contact with the exhaust gases will cool down smoothly. In this situation, the turbo timer makes life much easier. He will make sure that the hot car engine idles for several minutes, cooling the turbocharging elements, even if the owner has already left and closed his car. However, many security alarms have a similar function.

Engine power can also be increased by boosting. For supercharging, special compressors are used, driven from the crankshaft, part of the power is spent or gas turbine in which air or a combustible mixture is compressed before entering the cylinders. Pressurization systems The most typical pressurization schemes are: mechanical pressurization; turbocharger gas turbine centrifugal compressor; combined mechanical gas turbine pressurization; the compressor is located before the carburetor, sealing is needed; ...


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LECTURE 15

BLOWING SYSTEM

1 General information on engine charging

The main trends in the improvement of the internal combustion engine is the increase in power while reducing the consumption of fuel and toxic components of the exhaust gases. Analysis of the development of land transport means shows that piston engines will retain their leading positions for a long time to come. It is customary to evaluate the design of the engine by the liter power.

Basically, the increase in power is associated with an increase in the number of revolutions of the engine crankshaft. An increase in the number of revolutions is effective if the filling ratio is large. To this end, it is necessary to reduce losses in the intake and exhaust systems, use inertial phenomena in them and improve the gas distribution systems. To increase the effective power with an increase in the number of revolutions, it is necessary to reduce mechanical losses (the use of appropriate materials, oils, temperature stability, oil purification from mechanical impurities and its cooling, precision in the manufacture of parts and the quality of mechanical surface treatment).

Engine power can also be increased by boosting. For supercharging, special compressors are used driven by the crankshaft (part of the power is expended) or gas turbine, in which air or a combustible mixture is compressed before entering the cylinders. The charge is compressed faster than the temperature rise of the charge, so the charge density after compression is greater than the charge density before the compressor. The mass amount of charge entering the engine cylinder per cycle will be greater than when it is injected from the atmosphere.

2 Pressurization systems

The most typical pressurization schemes are:

  • mechanical pressurization;
  • turbocharged supercharging (gas turbine + centrifugal compressor);
  • combined supercharging (mechanical + gas turbine);
  • the compressor is located before the carburetor (sealing is needed);
  • the compressor is located after the carburetor (mixture formation improves, the operating conditions of the compressor blades deteriorate due to fuel);
  • impulse pressurization system;
  • non-pulse pressurization system.

Blade-centrifugal compressors are most widely used for pressurization. The main parameters of a compressor are the pressure ratio, compressor capacity and adiabatic efficiency. The work expended on compressing 1 kg of air in the compressor from pressure Po to Pk (adiabatic compression) is determined by:

In reality, the compression process occurs in the presence of both heat exchange with the environment and internal losses, which increases the work expended. This is taken into account by the adiabatic efficiency (0.65 ─ when the degree of pressure increase is equal to 1.3. With an increase in the degree, the efficiency decreases to 0.5). To achieve high boost pressures, rotary gear compressors are used.

High-speed motors use high-speed centrifugal or axial compressors (). With a decrease in efficiency and an increase in the degree of pressurization, the work expended on compressing the charge in the compressor and the temperature increase significantly, while the efficiency of pressurization decreases. With an increase in the degree of boost above a certain value, the effective power does not increase due to a decrease in the mechanical efficiency of the engine due to an increase in the power spent on the compressor drive.

Boosting slightly changes the nature of the combustion process due to the increase in pressure and temperature at the end of compression. When supercharged, the amount of fuel involved in combustion increases, therefore, the maximum values ​​of pressure and temperature of the end of combustion increase, and the thermal tension of parts increases. Better cooling of the valves occurs when the valves are closed during pressurization. These circumstances should be taken into account when using pressurization.

In carburetor engines, the use of supercharging is limited by the conditions for the occurrence of knocking combustion and is most often used when operating cars in mountainous conditions. If supercharging is used in a carburetor engine, a compression ratio correction is required. The use of relatively high boost pressures ( more than 0.2 MPa ) requires a change in valve timing, the use of a refrigerator to reduce the charge temperature after compression. The use of supercharging is most effective in diesel engines, where the increase in boost pressure is limited only by the thermal and mechanical strength of the engine structure. In this case, the power of the burner increases by 20-30% and the average effective pressure increases to 0.9-0.95 MPa.

3 Gas turbine supercharging

In the case of a GHP, a part of the energy of the exhaust gases is used for air compression and its injection. This makes it possible to partially utilize the difference between the pressure at the end of the expansion process in the engine cylinder and atmospheric air pressure. Engine power during GTN can increase up to 50%, the toxicity of exhaust gases is reduced. The design of the engine includes the use of appropriate materials, which increases the cost of manufacturing the engine, but the cost of the engine per unit of power is less than that of a naturally aspirated one. Air enters the compressor through an inlet in the center of the housing. The impeller and the guide vane provide an increase in potential and kinetic energy, then the air enters the diffuser and the air collector, from where it is distributed over the cylinders when the valve is opened. The absolute speed of air movement in the wheel reaches 300-350 m / s.

The turbocharger consists of a single-stage centrifugal compressor and a radial centripetal turbine. The main components of a turbocharger are: compressor stage, turbine stage and bearing assembly with seals. The compressor and turbine wheels are located at opposite ends of the rotor shaft cantilever relative to the bearings. The compressor impeller is cast from an AL4 alloy into plaster molds obtained from elastic models. The wheel is put on the shaft with an interference fit, therefore, when installed on the shaft, it heats up to 1100-1300 degrees C. The turbine impeller of a semi-open type with radial blades is manufactured by investment casting from a heat-resistant nickel alloy such as INCO-713S, ANV-300 and the like. It is connected to the shaft by friction welding. The body is made of creep-resistant cast iron. The turbocharger uses a “floating” plain bearing with a non-rotating mono-bush. The rotor is held from axial movements on both sides by bushings with ring holders pressed onto the rotor shaft of the turbocharger. Bearing lubrication is carried out from the engine lubrication system, under pressure, into the bearing housing. For stable engine operation at all speeds, reducing the "turbo lag" effect, a pressure control system is applied, with the help of a regulator, by bypassing the gas by the turbine.

Exhaust gases are fed to the nozzle blades in the housing. When the gas passes through the nozzle apparatus, its speed increases. At this speed, the gas enters the turbine impeller blade channels. The tangential action of the gas jet on the blades causes a torque to appear. A rotating outlet straightening device is installed at the outlet of the turbine. The peripheral speed of the turbocharger impellers is determined by the head developed by the turbocharger. V = 280-350 m / s. At an average temperature of about 700 degrees Celsius or more, the turbine wheels are made of nickel-based alloys. To ensure high throttle response of the turbocharger, efforts are made to reduce the outer diameter and moment of inertia of the impeller. The rotational speed of the rotor is calculated from the peripheral speed and diameter of the impeller, which can reach 50,000-80000 rpm.

4 Characteristics of supercharged automobile engines

The design characteristics of the turbocharger should provide a torque rise pattern similar to that of a naturally aspirated engine. In this case, the maximum air supply should occur at such a high-speed mode at which the torque is maximum. With an increase in the cycle flow, the excess air ratio decreases, but its reduction should be such that there is no increase in the smoke of the exhaust gases. Separate designs of the turbocharger have adjustable nozzle channels, which, with a decrease in the crankshaft speed, using a special device, turn the nozzle blades towards a decrease in the flow area. As a result, the gas pressure at the inlet increases and the flow rate increases, which increases the frequency of rotation of the TK shaft and the pressure of the fresh charge. Specific fuel consumption remains practically the same with increasing engine power.

In the pipelines of high-speed automobile engines, fluctuations in the gas flow occur during the intake and exhaust process. This phenomenon in the intake and exhaust pipes can be used for dynamic boosting. If you adjust the exhaust system so that by the end of the exhaust process, at the time the valves close, a vacuum develops near the exhaust valve, then the amount of residual gases will decrease, and the filling of the cylinder will improve. With a similar organization of the intake process at the end of the intake, the pressure of the fresh charge increases, which leads to an improvement in the filling of the cylinder. The dynamic exhaust system is tuned by changing the length of the exhaust pipe for each cylinder group. A properly tuned exhaust and intake system provides an increase in effective engine power by up to 10%.

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