As mentioned above, thermal expansion is used in an internal combustion engine. But how it is applied and what function it performs, we will consider using the example of the operation of a piston internal combustion engine. An engine is an energy-power machine that converts any energy into mechanical work... Engines in which mechanical work is created as a result of the conversion of thermal energy are called thermal motors. Thermal energy is obtained by burning any kind of fuel. A heat engine, in which part of the chemical energy of the fuel combusted in the working cavity is converted into mechanical energy, is called a piston engine internal combustion... (Soviet encyclopedic dictionary)
3. 1. Classification of internal combustion engines
As mentioned above, ICEs, in which the process of fuel combustion with the release of heat and its transformation into mechanical work, takes place directly in the cylinders, is the most widespread as power plants for cars. But in most modern cars, internal combustion engines are installed, which are classified according to various criteria: external mixture formation in which the combustible mixture is prepared outside the cylinders (carburetor and gas), and engines with internal mixture formation (the working mixture is formed inside the cylinders) - diesel engines; By the way of carrying out the working cycle - four-stroke and two-stroke; According to the number of cylinders - single-cylinder, two-cylinder and multi-cylinder; According to the arrangement of the cylinders - engines with a vertical or inclined arrangement of cylinders in one row, V-shaped with an arrangement of cylinders at an angle (with an arrangement of cylinders at an angle of 180, the engine is called an engine with opposite cylinders, or opposed); By cooling method - for engines with liquid or air cooled; By the type of fuel used - gasoline, diesel, gas and multi-fuel; By the compression ratio. Depending on the degree of compression, a distinction is made between
engines of high (E = 12 ... 18) and low (E = 4 ... 9) compression; By the method of filling the cylinder with a fresh charge: a) naturally aspirated engines, in which air or a combustible mixture is admitted due to vacuum in the cylinder during the suction stroke of the piston;) supercharged engines, in which air or a combustible mixture is injected into the working cylinder under pressure, created by the compressor, in order to increase the charge and obtain increased engine power; According to the frequency of rotation: low-speed, high-speed, high-speed; By purpose, stationary engines are distinguished, auto-tractor, ship, diesel, aviation, etc.
3.2. Fundamentals of piston internal combustion engines
Reciprocating internal combustion engines consist of mechanisms and systems that perform their assigned functions and interact with each other. The main parts of such an engine are the crank mechanism and the gas distribution mechanism, as well as the power supply, cooling, ignition and lubrication systems.
The crank mechanism converts the linear reciprocating motion of the piston into rotational motion of the crankshaft.
The gas distribution mechanism ensures the timely admission of the combustible mixture into the cylinder and the removal of combustion products from it.
The power system is designed for the preparation and supply of a combustible mixture into the cylinder, as well as for the removal of combustion products.
The lubrication system serves to supply oil to the interacting parts in order to reduce the friction force and partially cool them, along with this, the oil circulation leads to the washing off of carbon deposits and the removal of wear products.
The cooling system maintains a normal operating temperature of the engine, providing heat removal from the parts of the cylinders of the piston group and the valve mechanism that are very hot during the combustion of the working mixture.
The ignition system is designed to ignite the working mixture in the engine cylinder.
So, a four-stroke piston engine consists of a cylinder and a crankcase, which is closed from below by a sump. Inside the cylinder, a piston with compression (sealing) rings moves, in the form of a glass with a bottom in the upper part. The piston through the piston pin and the connecting rod is connected to crankshaft, which rotates in the main bearings located in the crankcase. The crankshaft consists of main journals, cheeks and connecting rod journals. Cylinder, piston, connecting rod and crankshaft make up the so-called crank mechanism. From above, the cylinder is covered with a head with valves, the opening and closing of which is strictly coordinated with the rotation of the crankshaft, and, consequently, with the movement of the piston.
The movement of the piston is limited to two extreme positions at which its speed is zero. The topmost position of the piston is called top dead center (TDC), its bottommost position is the bottom dead center (BDC).
The non-stop movement of the piston through the dead center is provided by a flywheel in the form of a disk with a massive rim. The distance traveled by the piston from TDC to BDC is called the piston stroke S, which is equal to twice the radius R of the crank: S = 2R.
The space above the piston crown when it is at TDC is called the combustion chamber; its volume is denoted by Vc; the space of the cylinder between two dead points (BDC and TDC) is called its working volume and is denoted by Vh. The sum of the volume of the combustion chamber Vc and the working volume Vh is the total volume of the cylinder Va: Va = Vc + Vh. The working volume of the cylinder (it is measured in cubic centimeters or meters): Vh = pD ^ 3 * S / 4, where D is the cylinder diameter. The sum of all the working volumes of the cylinders of a multi-cylinder engine is called the working volume of the engine, it is determined by the formula: Vр = (pD ^ 2 * S) / 4 * i, where i is the number of cylinders. The ratio of the total volume of the cylinder Va to the volume of the combustion chamber Vc is called the compression ratio: E = (Vc + Vh) Vc = Va / Vc = Vh / Vc + 1. Compression ratio is an important parameter for internal combustion engines because greatly affects its efficiency and power.
Definition.
Piston engine- one of the variants of the internal combustion engine, which works by converting the internal energy of the burning fuel into the mechanical work of the piston's translational motion. The piston is set in motion when the working fluid expands in the cylinder.
The crank mechanism converts the forward motion of the piston into the rotational motion of the crankshaft.
The working cycle of the engine consists of a sequence of strokes of one-way forward strokes of the piston. Engines with two and four strokes are subdivided.
The principle of operation of two-stroke and four-stroke piston engines.
Number of cylinders in piston engines may vary depending on the design (from 1 to 24). The volume of the engine is considered to be equal to the sum of the volumes of all cylinders, the capacity of which is found by the product of the cross section and the stroke of the piston.
V piston engines of various designs, the process of fuel ignition occurs in different ways:
Electrospark discharge that forms on the spark plugs. These engines can run on both gasoline and other fuels (natural gas).
By compressing the working fluid:
V diesel engines operating on diesel fuel or gas (with a 5% addition of diesel fuel), air is compressed, and when the piston reaches the maximum compression point, fuel is injected, which ignites from contact with heated air.
Compression engines... The fuel supply to them is exactly the same as in gasoline engines... Therefore, for their operation, a special composition of fuel (with admixtures of air and diethyl ether) is required, as well as precise adjustment of the compression ratio. Compressor engines have found their way into the aircraft and automotive industries.
Incandescent engines... The principle of their operation is in many ways similar to the compression model engines, but it was not without design features... The role of ignition in them is performed by a glow plug, the glow of which is maintained by the energy of the fuel that burns in the previous cycle. The composition of the fuel is also special, based on methanol, nitromethane and castor oil. Such engines are used both on cars and on airplanes.
Calorizing motors... In these engines, ignition occurs when the fuel comes into contact with hot parts of the engine (usually the piston crown). Open-hearth gas is used as fuel. They are used as drive motors in rolling mills.
Fuels used in piston engines:
Liquid fuel- diesel fuel, gasoline, alcohols, biodiesel;
Gases- natural and biological gases, liquefied gases, hydrogen, gaseous products of oil cracking;
Produced in the gasifier from coal, peat and wood, carbon monoxide is also used as a fuel.
The operation of piston engines.
Engine cycles detailed in technical thermodynamics. Different cyclograms are described by different thermodynamic cycles: Otto, Diesel, Atkinson or Miller and Trinkler.
Reasons for piston engine breakdowns.
Efficiency of a piston internal combustion engine.
The maximum efficiency that was obtained on piston engine is 60%, i.e. slightly less than half of the burning fuel is spent on heating engine parts, and also comes out with heat exhaust gases... In this connection, it is necessary to equip engines with cooling systems.
Cooling systems classification:
Air CO- give off heat to the air due to the ribbed outer surface of the cylinders. Are applied
more on weak engines (tens of hp), or on powerful aircraft engines that are cooled by a fast air stream.
Liquid CO- a liquid (water, antifreeze or oil) is used as a coolant, which is pumped through the cooling jacket (channels in the walls of the cylinder block) and enters the cooling radiator, in which it is cooled by air flows, natural or from fans. Rarely, but metallic sodium is also used as a coolant, which is melted by the heat of a warming engine.
Application.
Piston engines, due to their power range (1 watt - 75,000 kW), have gained great popularity not only in the automotive industry, but also in aircraft and shipbuilding. They are also used to drive military, agricultural and construction equipment, power generators, water pumps, chainsaws and other machines, both mobile and stationary.
Rotary piston engine(RPD), or Wankel engine. Internal combustion engine developed by Felix Wankel in 1957 in collaboration with Walter Freude. In RPD, the function of a piston is performed by a three-vertex (triangular) rotor, which makes rotational movements inside a cavity of a complex shape. After the wave of experimental car and motorcycle models in the 60s and 70s of the twentieth century, interest in RPDs declined, although a number of companies are still working to improve the design of the Wankel engine. Currently, the RPD is equipped with passenger cars Mazda... The rotary piston engine finds application in modeling.
Principle of operation
The force of the gas pressure from the burnt air-fuel mixture drives the rotor, which is mounted through bearings on the eccentric shaft. The movement of the rotor relative to the motor housing (stator) is carried out through a pair of gears, one of which, bigger size, fixed on the inner surface of the rotor, the second, supporting, smaller, rigidly attached to the inner surface of the engine side cover. The interaction of the gears leads to the fact that the rotor makes circular eccentric movements, contacting the edges with the inner surface of the combustion chamber. As a result, three isolated chambers of variable volume are formed between the rotor and the engine casing, in which the processes of compression of the fuel-air mixture, its combustion, expansion of gases exerting pressure on the working surface of the rotor and cleaning the combustion chamber from exhaust gases take place. The rotational motion of the rotor is transmitted to an eccentric shaft mounted on bearings and transmitting torque to the transmission mechanisms. Thus, two mechanical pairs work simultaneously in the RPD: the first one regulates the movement of the rotor and consists of a pair of gears; and the second one converts the circular motion of the rotor into rotation of the eccentric shaft. The gear ratio of the rotor and stator gears is 2: 3, therefore, in one full revolution of the eccentric shaft, the rotor has time to turn 120 degrees. In turn, for one complete revolution of the rotor in each of the three chambers formed by its edges, a complete four-stroke cycle of the internal combustion engine is performed.
RPD scheme
1 - inlet window; 2 outlet window; 3 - case; 4 - combustion chamber; 5 - stationary gear; 6 - rotor; 7 - gear wheel; 8 - shaft; 9 - spark plug
Advantages of the RPD
The main advantage of a rotary piston engine is its simplicity of design. The RPD has 35-40 percent fewer parts than a four-stroke piston engine. The RPD lacks pistons, connecting rods, and a crankshaft. In the "classic" version of the RPD, there is no gas distribution mechanism either. The fuel-air mixture enters the working cavity of the engine through the inlet window, which opens the edge of the rotor. The exhaust gases are discharged through the exhaust port, which again crosses the edge of the rotor (this is reminiscent of the gas distribution device of a two-stroke piston engine).
Special mention should be made of the lubrication system, which is practically absent in the simplest version of the RPD. The oil is added to the fuel, just like a two-stroke motorcycle engine. Friction pairs (primarily the rotor and the working surface of the combustion chamber) are lubricated by the fuel-air mixture itself.
Since the rotor mass is small and is easily balanced by the mass of the eccentric shaft counterweights, the RPD has a low vibration level and good uniformity of operation. In vehicles with RPD, it is easier to balance the engine, having achieved a minimum level of vibration, which has a good effect on the comfort of the car as a whole. Twin-rotor motors are particularly smooth running, in which the rotors themselves are vibration-reducing balancers.
Another attractive quality of the RPD is the high power density at high revs eccentric shaft. This makes it possible to achieve excellent speed characteristics from a car with a RPD with relatively low fuel consumption. Low inertia of the rotor and increased power density in comparison with piston internal combustion engines improve vehicle dynamics.
Finally, an important advantage of the RPD is its small size. Rotary engine less than a piston four-stroke engine of the same power by about half. And this allows you to more efficiently use the space of the engine compartment, more accurately calculate the location of the transmission units and the load on the front and rear axles.
Disadvantages of RAP
The main disadvantage of a rotary piston engine is the low efficiency of sealing the gap between the rotor and the combustion chamber. The RPD rotor of a complex shape requires reliable seals not only along the edges (and there are four of them on each surface - two on the top, two on the side edges), but also on the side surface in contact with the engine covers. In this case, the seals are made in the form of spring-loaded strips of high-alloy steel with particularly precise processing of both working surfaces and ends. The tolerances for metal expansion inherent in the design of seals from heating impair their characteristics - it is almost impossible to avoid gas breakthrough at the end sections of the sealing plates (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. The designers have found new materials for the seals. However, there is no need to talk about any breakthrough yet. Seals are still the bottleneck of the RPD.
The complex rotor sealing system requires effective lubrication of the friction surfaces. RPD consumes more oil than a four-stroke piston engine (from 400 grams to 1 kilogram per 1000 kilometers). In this case, the oil burns along with the fuel, which has a bad effect on the environmental friendliness of the engines. There are more substances hazardous to human health in the exhaust gases of the RPD than in the exhaust gases of piston engines.
Special requirements are also imposed on the quality of the oils used in the RPD. This is due, firstly, to the tendency to increased wear (due to the large area of contacting parts - the rotor and the internal chamber of the engine), and secondly, to overheating (again due to increased friction and due to the small size of the engine itself ). For RPD, irregular oil changes are deadly - since abrasive particles in old oil sharply increase engine wear and engine overcooling. Starting a cold engine and insufficient warming up leads to the fact that there is little lubrication in the contact zone of the rotor seals with the surface of the combustion chamber and side covers. If the piston engine jams due to overheating, then the RPD most often - during the start of a cold engine (or when driving in cold weather, when the cooling is excessive).
In general, the operating temperature of the RPD is higher than that of reciprocating engines. The most thermally stressed area is the combustion chamber, which has a small volume and, accordingly, an increased temperature, which complicates the process of igniting the fuel-air mixture (RPDs, due to the extended shape of the combustion chamber, are prone to detonation, which can also be attributed to the disadvantages of this type of engine). Hence the exactingness of the RPD to the quality of the candles. Usually they are installed in these engines in pairs.
Rotary piston engines with excellent power and speed characteristics turn out to be less flexible (or less elastic) than piston ones. They deliver optimal power only at high enough rpm, which forces designers to use RPD in tandem with multi-stage gearboxes and complicates the design automatic boxes gear. Ultimately, RPDs are not as economical as they should be in theory.
Practical applications in the automotive industry
RPDs were most widespread in the late 60s and early 70s of the last century, when the patent for the Wankel engine was bought by 11 leading car manufacturers in the world.
In 1967, the German company NSU released a serial a car business class NSU Ro 80. This model was produced for 10 years and sold around the world in the amount of 37,204 copies. The car was popular, but the shortcomings of the RPD installed in it, in the end, spoiled the reputation of this wonderful car. Against the background of durable competitors, the NSU Ro 80 model looked "pale" - mileage up to overhaul engine with the declared 100 thousand kilometers did not exceed 50 thousand.
The concern Citroen, Mazda, VAZ experimented with RPD. The greatest success was achieved by Mazda, which released its passenger car with RPD back in 1963, four years before the appearance of the NSU Ro 80. Today, Mazda is equipping RX series sports cars with RPDs. Modern cars The Mazda RX-8 has been spared many of the disadvantages of Felix Wankel's RPDs. They are quite environmentally friendly and reliable, although they are considered "capricious" among car owners and repair specialists.
Practical application in the motorcycle industry
In the 70s and 80s, some motorcycle manufacturers experimented with RPDs - Hercules, Suzuki and others. Currently, small-scale production of "rotary" motorcycles is established only at Norton, which produces the NRV588 model and prepares the NRV700 motorcycle for serial production.
Norton NRV588 is a sports bike equipped with a twin-rotor engine with a total volume of 588 cubic centimeters and developing a power of 170 Horse power... With a dry weight of a motorcycle of 130 kg, the power-to-weight ratio of a sportbike looks literally prohibitive. The engine of this machine is equipped with variable intake and electronic fuel injection systems. All that is known about the NRV700 model is that the RPD power of this sportbike will reach 210 hp.
- ensures the transfer of mechanical forces to the connecting rod;
- is responsible for sealing the fuel combustion chamber;
- ensures timely removal of excess heat from the combustion chamber
The operation of the piston takes place in difficult and in many ways dangerous conditions - with increased temperature conditions and increased loads, therefore it is especially important that pistons for engines are distinguished by efficiency, reliability and wear resistance. That is why, for their production, light, but ultra-strong materials are used - heat-resistant aluminum or steel alloys. Pistons are made by two methods - casting or stamping.
Piston design
The engine piston has a fairly simple design, which consists of the following parts:
Volkswagen AG
- ICE piston head
- Piston pin
- Retaining ring
- Boss
- Connecting rod
- Steel insert
- Compression ring first
- Compression ring second
- Oil scraper ring
The design features of the piston in most cases depend on the type of engine, the shape of its combustion chamber and the type of fuel that is used.
Bottom
The bottom can have a different shape depending on the functions it performs - flat, concave and convex. The concave bottom provides a more efficient combustion chamber, but it contributes to more deposits during combustion. The convex shape of the bottom improves the performance of the piston, but at the same time reduces the efficiency of the combustion process of the fuel mixture in the chamber.
Piston rings
Below the bottom there are special grooves (grooves) for installation piston rings... The distance from the bottom to the first compression ring is called the fire belt.
Piston rings are responsible for a secure connection between the cylinder and piston. They provide reliable tightness due to a tight fit to the cylinder walls, which is accompanied by a stressful friction process. Engine oil is used to reduce friction. For the manufacture of piston rings, a cast iron alloy is used.
The number of piston rings that can be installed in a piston depends on the type of engine used and its purpose. Systems with one oil scraper ring and two compression rings (first and second).
Oil scraper ring and compression rings
The oil scraper ring ensures the timely elimination of excess oil from the inner walls of the cylinder, and the compression rings prevent gases from entering the crankcase.
The first compression ring absorbs most of the inertial forces during piston operation.
To reduce the loads in many engines, a steel insert is installed in the annular groove, which increases the strength and compression ratio of the ring. Compression rings can be made in the form of a trapezoid, barrel, cone, with a cutout.
The oil scraper ring in most cases is equipped with many holes for oil drainage, sometimes with a spring expander.
Piston pin
This is a tubular part that is responsible for the reliable connection of the piston to the connecting rod. Made of steel alloy. When installing the piston pin in the bosses, it is tightly fixed with special retaining rings.
The piston, piston pin and rings together create a so-called piston group engine.
Skirt
The guiding part of the piston device, which can be made in the form of a cone or barrel. The piston skirt is equipped with two bosses for connecting to the piston pin.
To reduce frictional losses, a thin layer of antifriction agent is applied to the surface of the skirt (often graphite or molybdenum disulfide is used). The lower part of the skirt is equipped with an oil scraper ring.
A mandatory process of operation of a piston device is its cooling, which can be carried out by the following methods:
- spraying oil through holes in the connecting rod or a nozzle;
- the movement of oil along the coil in the piston head;
- supplying oil to the area of the rings through the annular channel;
- oil mist
Sealing part
The sealing part and the crown are connected in the form of a piston head. In this part of the device there are piston rings - oil scraper and compression rings. The ring passages have small holes through which the used oil enters the piston and then flows into the engine crankcase.
In general, the piston of an internal combustion engine is one of the most heavily loaded parts, which is subjected to strong dynamic and, at the same time, thermal effects. This imposes increased requirements both on the materials used in the production of pistons and on the quality of their manufacture.
When fuel is burned, thermal energy is released. An engine in which fuel is burned directly inside the working cylinder and the energy of the resulting gases is perceived by a piston moving in the cylinder is called a piston engine.
So, as mentioned earlier, this type of engine is the main one for modern cars.
In such engines, the combustion chamber is located in a cylinder, in which the thermal energy from the combustion of the air-fuel mixture is converted into mechanical energy of the piston moving translationally and then by a special mechanism, which is called a crank-connecting rod, is converted into rotational energy of the crankshaft.
At the place of formation of a mixture consisting of air and fuel (combustible), piston internal combustion engines are divided into engines with external and internal conversion.
At the same time, engines with external mixture formation, according to the type of fuel used, are divided into carburetor and injection engines operating on light liquid fuel (gasoline) and gas engines operating on gas (gas generator, lighting, natural gas, etc.). Compression ignition engines are diesel engines (diesels). They run on heavy fuel oil (diesel). In general, the design of the engines themselves is practically the same.
The working cycle of four-stroke piston engines occurs when the crankshaft makes two revolutions. By definition, it consists of four separate processes (or strokes): intake (1 stroke), compression of the air-fuel mixture (2 stroke), power stroke (3 stroke) and exhaust (4 stroke).
The change in the engine operation strokes is provided with the help of a gas distribution mechanism consisting of a camshaft, a transmission system of pushers and valves that isolate the working space of the cylinder from the external environment and mainly provide a change in valve timing. Due to the inertia of gases (features of gas dynamics processes), the intake and exhaust strokes for real engine overlap, which means they work together. At high speeds, phase overlap has a positive effect on engine performance. On the contrary, the higher it is at low revs, the lower the engine torque. In work modern engines this phenomenon is taken into account. They create devices that allow you to change the valve timing during operation. There are various designs of such devices, the most suitable of which are electromagnetic valve timing devices (BMW, Mazda).
Carbureted internal combustion engines
V carburetor engines the air-fuel mixture is prepared before it enters the engine cylinders, in a special device - in the carburetor. In such engines, a combustible mixture (a mixture of fuel and air) that has entered the cylinders and mixed with the residual exhaust gases (working mixture) is ignited by an external source of energy - an electric spark of the ignition system.
Injection ICE
In such engines, due to the presence of spray nozzles that inject gasoline into the intake manifold, mixture formation with air occurs.
Gas internal combustion engines
In these engines, the gas pressure after exiting gas reducer is greatly reduced and brought to close to atmospheric, after which it is sucked in with the help of an air-gas mixer, injected by means of electric nozzles (similarly injection engines) into the engine intake manifold.
Ignition, as in previous types of engines, is carried out from the spark of a candle, slipping between its electrodes.
Diesel internal combustion engines
In diesel engines, mixture formation takes place directly inside the engine cylinders. Air and fuel enter the cylinders separately.
At the same time, at first only air enters the cylinders, it is compressed, and at the moment of its maximum compression, a stream of finely atomized fuel is injected into the cylinder through a special nozzle (the pressure inside the cylinders of such engines reaches much higher values than in engines of the previous type), the formed mixtures.
In this case, the mixture is ignited as a result of an increase in the temperature of the air with its strong compression in the cylinder.
Among the disadvantages diesel engines it is possible to distinguish a higher, in comparison with the previous types of piston engines, the mechanical stress of its parts, especially the crank mechanism, which requires improved strength properties and, as a consequence, large dimensions, weight and cost. It is increased due to the complicated design of engines and the use of better materials.
In addition, such engines are characterized by inevitable soot emissions and an increased content of nitrogen oxides in the exhaust gases due to the heterogeneous combustion of the working mixture inside the cylinders.
Gas-diesel internal combustion engines
The principle of operation of such an engine is similar to that of any type of gas engine.
The air-fuel mixture is prepared according to a similar principle, by supplying gas to an air-gas mixer or to the intake manifold.
However, the mixture is ignited with an ignition portion of diesel fuel, injected into the cylinder by analogy with the operation of diesel engines, and not using an electric spark plug.
Rotary piston internal combustion engines
In addition to the well-established name, this engine is named after the scientist-inventor who created it and is called the Wankel engine. Proposed at the beginning of the 20th century. Currently, the manufacturers Mazda RX-8 are engaged in such engines.
The main part of the engine is formed by a triangular rotor (analogue of a piston), rotating in a chamber of a specific shape, according to the design of the inner surface, reminiscent of the number "8". This rotor acts as a crankshaft piston and a gas distribution mechanism, thus eliminating the valve timing system required for piston engines. It performs three full working cycles in one revolution, which allows one such engine to replace a six-cylinder piston engine. positive qualities, among which also the fundamental simplicity of its design, has disadvantages that prevent its widespread use. They are associated with the creation of durable reliable seals of the chamber with the rotor and the construction of the necessary engine lubrication system. The working cycle of rotary piston engines consists of four strokes: intake of the air-fuel mixture (1 stroke), compression of the mixture (2 stroke), expansion of the combustion mixture (3 stroke), exhaust (4 stroke).
Rotary-combustion internal combustion engines
This is the same engine used in the Yo-mobile.
Gas turbine internal combustion engines
Already today, these engines are successfully able to replace piston internal combustion engines in automobiles. And although the design of these engines has reached this level of perfection only in the last few years, the idea of using gas turbine engines in automobiles has arisen for a long time. The real possibility of creating reliable gas turbine engines is now provided by the theory of blade engines, which has reached a high level of development, metallurgy and the technology of their production.
What is a gas turbine engine? To do this, let's look at its schematic diagram.
The compressor (item 9) and the gas turbine (item 7) are on the same shaft (item 8). The gas turbine shaft rotates in bearings (key 10). The compressor takes air from the atmosphere, compresses it and directs it into the combustion chamber (item 3). Fuel pump(item 1) is also driven by the turbine shaft. It supplies fuel to the injector (item 2), which is installed in the combustion chamber. The gaseous products of combustion enter through the guide vane (item 4) of the gas turbine onto the blades of its impeller (item 5) and force it to rotate in a given direction. Exhaust gases are released into the atmosphere through the branch pipe (item 6).
And although this engine is full of flaws, they are gradually eliminated as the design develops. At the same time, in comparison with a piston internal combustion engine, a gas turbine internal combustion engine has a number of significant advantages. First of all, it should be noted that, like a steam turbine, a gas turbine can develop high speeds. This allows you to get more power from smaller engines and lighter in weight (almost 10 times). In addition, the only type of movement in gas turbine is rotational. A piston engine, in addition to a rotary engine, has reciprocating piston movements and complex connecting rod movements. Also, gas turbine engines do not require special cooling and lubrication systems. The absence of significant friction surfaces with a minimum number of bearings ensures long-term operation and high reliability gas turbine engine... Finally, it is important to note that their nutrition is carried out using kerosene or diesel fuel, i.e. cheaper types than gasoline. The reason that restrains the development of automobile gas turbine engines is the need to artificially limit the temperature of the gases entering the turbine blades, since high-fire metals are still very expensive. As a result, it reduces the useful use (efficiency) of the engine and increases the specific fuel consumption (the amount of fuel per 1 hp). For passenger and cargo car engines the gas temperature has to be limited to within 700 ° C, and in aircraft engines up to 900 ° C. However, today there are some ways to increase the efficiency of these engines by removing the heat of the exhaust gases to heat the air entering the combustion chambers. The solution to the problem of creating a highly efficient automobile gas turbine engine largely depends on the success of work in this area.
Combined internal combustion engines
A great contribution to the theoretical aspects of the operation and creation of combined engines was made by the engineer of the USSR, Professor A.N. Shelest.
Alexey Nesterovich Shelest
These engines are a combination of two machines: reciprocating and vane, which can be a turbine or compressor. Both of these machines are important elements workflow. An example of such a turbocharged engine. At the same time, in a conventional piston engine, air is forced into the cylinders with the help of a turbocharger, which makes it possible to increase the engine power. It is based on the use of the energy of the exhaust gas stream. It acts on the turbine impeller, which is attached to the shaft on one side. And spins it. The compressor blades are located on the other side of the same shaft. Thus, with the help of the compressor, air is pumped into the engine cylinders due to vacuum in the chamber on the one hand and forced air supply, on the other hand, a large amount of a mixture of air and fuel enters the engine. As a result, the volume of combustible fuel increases and the resulting combustion gas occupies a larger volume, which creates a greater force on the piston.
Two-stroke internal combustion engines
This is the name of an internal combustion engine with an unusual gas distribution system. It is realized in the process of the passage of the reciprocating piston through two pipes: inlet and outlet. You can find its foreign designation "RCV".
The engine's work processes take place during one crankshaft revolution and two piston strokes. The principle of operation is as follows. First, the cylinder is purged, which means the intake of the combustible mixture with the simultaneous intake of the exhaust gases. Then the working mixture is compressed, at the moment of turning the crankshaft by 20-30 degrees from the position of the corresponding BDC when moving to TDC. And the working stroke, the length of which is the piston stroke from the top dead center (TDC) before reaching the bottom dead center (BDC) by 20-30 degrees in terms of crankshaft revolutions.
There are clear disadvantages two-stroke engines... Firstly, the weak link in the two-stroke cycle is engine purging (again, from the point of view of gas dynamics). This happens on the one hand due to the fact that the separation of the fresh charge from the exhaust gases cannot be ensured, i.e. losses are inevitable in essence flying out to exhaust pipe fresh mixture (or air if we are talking about diesel). On the other hand, the working stroke lasts less than half a revolution, which already indicates a decrease in the engine efficiency. Finally, the duration of the extremely important gas exchange process, which in a four-stroke engine takes up half the operating cycle, cannot be increased.
Two-stroke engines are more complex and more expensive due to the mandatory use of a purge or pressurization system. Undoubtedly, the increased thermal stress of the parts of the cylinder-piston group requires the use of more expensive materials for individual parts: pistons, rings, cylinder liners. Also, the performance of the gas distribution functions by the piston imposes a limitation on the size of its height, which consists of the height of the piston stroke and the height of the blowing windows. This is not so critical in a moped, but it makes the piston much heavier when installed on vehicles that require significant power consumption. Thus, when power is measured in tens or even hundreds of horsepower, the increase in piston mass is very noticeable.
Nevertheless, some work was carried out in the direction of improving such engines. In Ricardo engines, special distribution sleeves with a vertical stroke were introduced, which was some attempt to make it possible to reduce the size and weight of the piston. The system turned out to be quite complex and very expensive to implement, so such engines were used only in aviation. It should be additionally noted that the exhaust valves (with direct-flow valve purging) have twice the heat intensity in comparison with the valves of four-stroke engines. In addition, the seats have a longer direct contact with the exhaust gases, and therefore a worse heat dissipation.
Six-stroke internal combustion engines
The work is based on the principle of operation of a four-stroke engine. Additionally, its design contains elements that, on the one hand, increase its efficiency, while on the other hand, reduce its losses. There are two different types of these motors.
In engines operating on the basis of Otto and Diesel cycles, there are significant heat losses during fuel combustion. These losses are used in the engine of the first design as additional power. In the designs of such engines, an additional fuel-air mixture is used as a working medium for the additional piston stroke, steam or air is used, as a result of which the power is increased. In these engines, after each fuel injection, the pistons move three times in both directions. In this case, there are two working strokes - one with fuel and the other with steam or air.
The following engines have been created in this area:
Bajulaz engine (from English Bajulaz). It was created by Bayoulas (Switzerland);
Crower's engine (from English Crower). Invented by Bruce Crower (USA);
Bruce Crower
Velozeta Engine (from English Velozeta) Was built in the College of Engineering (India).
The principle of operation of the second type of engine is based on the use in its design of an additional piston on each cylinder and located opposite the main one. The additional piston moves at a frequency that is halved in relation to the main piston, which provides six piston strokes per cycle. The additional piston, by its main purpose, replaces the traditional gas distribution mechanism of the engine. Its second function is to increase the compression ratio.
The main, independently created from each other, designs of such engines are two:
Beare Head engine. Invented by Malcolm Beer (Australia);
engine named "Charge pump" (from English German Charge pump). Invented by Helmut Kotmann (Germany).
What will happen to the internal combustion engine in the near future?
In addition to those indicated at the beginning of the article ICE disadvantages there is one more fundamental drawback that does not allow using the internal combustion engine separately from the vehicle's transmission. Power unit the car is formed by the engine in conjunction with the car's transmission. It allows the vehicle to move at all required driving speeds. But a separate internal combustion engine develops the highest power only in a narrow range of revolutions. This is why a transmission is needed. Only in exceptional cases do they dispense with the transmission. For example, in some aircraft designs.
