A compressor is any device that is designed to compress and supply air, as well as other gases under pressure. Where is this device used?
Automotive engineers, race car makers and speed buffs are constantly working on increasing engine power. One of the ways to increase it is to build a motor with a large internal volume, but large motors weigh a lot and, in addition, the costs of their production and maintenance are very high.
Photo. ProCharger D1SC - centrifugal compressor
The second way to increase the intensity of the engine is to create a unit of a standard size, but more efficient to use. More efficient recoil can be achieved by pumping more air into the combustion chamber, which allows more fuel to be supplied to the cylinder, which means that more power is achieved due to high pressure and, accordingly, strong gas emission. It is the compressor, which is also called a supercharger, that allows you to increase the air supply and increase the engine power.
In addition to the compressor, there is also a turbocharger. The difference between the two devices is in the way they extract energy. A conventional compressor is powered by energy that is mechanically transferred from the engine crankshaft through a belt or chain drive. As for the turbocharger, it works thanks to the compressed stream of exhaust gases that rotate the turbine.
How the compressor works
In order to understand how this mechanism works, consider the operation of a conventional four-stroke internal combustion engine. With the downward movement of the piston, a rarefaction of air is created, which, under the influence of atmospheric pressure, enters the combustion chamber. Once air enters the engine, it combines with the fuel mixture to create a charge that can be converted into usable kinetic energy through combustion. The spark plug creates combustion. Once the fuel oxidation reaction occurs, a large amount of energy is released. The force of this explosion drives the piston, and the force of this movement goes to the wheels, causing them to rotate.
The denser flow of the fuel / air mixture into the charge will create more violent explosions. But it should be understood that a certain amount of oxygen is required to burn a specific amount of fuel. The correct ratio is considered: 14 parts of air to 1 part of atmospheric air. This proportion is very important for the efficient operation of the power unit of the car and expresses the rule: "in order to burn more fuel, you need to supply more air."
This is the job of the compressor. It compresses air as it enters the engine, allowing more air to be filled into the engine and creating a pressure build-up. At the same time, more fuel can enter the engine, causing an increase in power. On average, the compressor adds 46% power and 31% torque.
The mechanical supercharger is started with a drive belt wrapped around a pulley that is connected to the pinion gear. The drive gear drives the blower gear. The compressor rotor draws in air, compresses it and throws it into the intake manifold. The compressor rotation speed is 50-60 thousand revolutions per minute. As a result, the blower increases the air supply to the machine engine by about 50%.
As hot air contracts, it loses its density and cannot expand much during an explosion. In this case, it cannot give as much energy as is produced when a cooler fuel-air mixture ignites with a spark plug. It can be concluded that in order for the blower to work with maximum efficiency, the compressed air at the outlet from the device must be cooled. The intercooler is engaged in the air cooling process. Hot air is cooled in the intercooler tubes using cold air or cold liquid, depending on the type of mechanism. Lowering the temperature of the air, increasing its density, makes the charge that enters the combustion chamber stronger.
Compressor types
Compressors are of three types: twin-screw, rotary and centrifugal. The main difference between the two is the way air is supplied to the intake manifold of an automobile engine.
A twin-screw blower consists of two rotors with air circulating inside. This design creates a lot of noise in the form of compressed air whistling, which is muffled by special engine noise insulation methods.
Photo. Twin screw compressor
A rotary supercharger is usually located at the top of an automobile engine and consists of rotating camshafts that move atmospheric air into the intake manifold. It is heavy and makes the vehicle heavier. In addition, the air flow in this type of compressor has an intermittent structure, which makes it the least efficient in comparison with other types of compressors.
Photo. Rotary compressor
A centrifugal blower is most effective for forcing pressure build-up inside a machine engine. It is an impeller rotating with tremendous force and forcing air into a small compressor housing. Centrifugal force pushes air to the edge of the impeller, forcing it to leave its cavity at great speed. Small blades around the impeller convert high-speed, low-pressure air into low-speed, high-pressure air.
Photo. Centrifugal compressor
Compressor advantages
The main advantage of the compressor is, of course, the increase in the power of the vehicle engine. Experts consider mechanical superchargers to be somewhat better than turbocharged ones because engines equipped with them do not have a delay in response to the driver pressing the gas pedal, because mechanical compressors are driven directly from the engine crankshaft. Turbochargers, in turn, are prone to lagging, since the exhaust gases pick up the speed required to spin up the turbines only after some time has elapsed.
Disadvantages of engines
Since the compressor is started by the engine crankshaft, this slightly reduces the power of the power unit. The compressor increases the load on the engine, so the engine must be strong enough to withstand strong explosions in the combustion chamber. Modern car manufacturers take this condition into account and create stronger units for engines designed to work in tandem with a compressor, which increases the cost of the car, as well as the cost of its maintenance.
In general, superchargers are the most efficient way to add horsepower or power to a vehicle's engine in other words. The compressor can add 50 to 100% power, which is why it is often installed in their cars by racers and fans of high-speed driving.
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 supercharger provides an increase in engine power 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.
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, the throttle valve is slightly open and the line valve is fully open, allowing 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 the compressor wheel of a turbine. 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 to eliminate turbo lag.
- 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.
Some 10 years ago, only a sports or tuned car could boast of a turbine or compressor. But today you will hardly surprise anyone with the "additional muscle" of the engine, because on many cars the manufacturing plant itself installs a unit that increases the engine power. And if you want to know what is the difference between an atmospheric, turbocharged and a compressor engine, then you have come to the right place, because this is what we will tell you about.
To begin with, we will mention that automobile engines can be divided into 2 groups: atmospheric and supercharged. Structurally, these types are very different, and the increase in engine power is different.
Aspirated engine basics
The atmospheric engine is perhaps the most complex in its design. In an atmospheric engine, the fuel-air mixture is fed into the cylinders without the slightest resistance, which means that it has undergone serious modifications. Secondly, the camshaft is very finely tuned in order to ensure the longest possible opening of the intake valve. Finally, the stroke and diameter are increased in order to provide even more engine power. As you can see, the naturally aspirated engine is structurally very complex, but flexible and responsive in operation.
The main highlight of the naturally aspirated engine is that it has a power reserve at any speed, instantly responds to pressing the accelerator pedal. This means that the naturally aspirated engine is the best at spinning up to maximum revs. At the same time, among the existing shortcomings, the most serious are high fuel consumption and a relatively low engine resource.
A little about turbocharged engines
The turbocharged engine is a classic of the genre. Most car owners give their preference to turbocharged engines. The principle of operation of a turbocharged engine is approximately the same as that of an atmospheric one. The fuel-air mixture is forced into the engine cylinders. The difference is only in pressure. In addition, depending on the wishes of the owner, it is possible to increase the pressure generated by the turbine, which will give an increase in power.
Nevertheless, although turbocharged engines are the most common of the types we consider, turbo engines still have some disadvantages:
- At first, the turbine gives an increase in power only at high engine speeds, at low speeds it is practically not felt.
- Secondly, turbocharged motors are characterized by such a phenomenon as turbofan. This means that the turbine does not immediately give an increase in power after you press the gas pedal to the floor, but after a few tenths of a second. This may be a small thing for city driving, but in motorsport it is a serious drawback. Finally, turbocharged engines are very sensitive to the lubrication system.
Compressor motors
The compressor on the engine is a kind that is driven by a belt drive. This means, the higher the engine speed, the more power it will receive. The compressor not only supplies the air / fuel mixture to the cylinders under pressure, but also blows them out when the inlet and outlet valves are in the half-open and half-closed positions. Thus, the compressor not only increases power, but also cleans the cylinders, allowing the engine to continuously operate at its maximum capacity.
Compressor motor an internal combustion engine, usually diesel, in which fuel is supplied to the cylinder with air compressed to 6 Mn / m 2 (60 kgf / cm 2). According to their design, diesel engines are subdivided into cross-head motors. Crosshead motor) and trunk motors (see. Trunk engine),
2- and 4-stroke. In a combustion chamber with direct-flow blowing, the average indicator pressure during smokeless combustion reaches 0.8-0.9 Mn / m 2 (8-9 kgf / cm 2). The capacity of the boiler is about 2.2-3.7 Mw (3000-5000 l. with.), rotation frequency - 180-500 rpm Due to the significant weight and dimensions, as well as the difficulty of adjusting the air pressure at different crankshaft rotational speeds, K. d. Are not used as transport vehicles (with the exception of ships). see also Diesel.
Great Soviet Encyclopedia. - M .: Soviet encyclopedia. 1969-1978 .
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