Rotary-piston engine (RPD), or Vankel engine. Internal combustion engine developed by Felix Vankel in 1957 in collaboration with Freud Walter. In the RPD, the piston function performs a three-service (triangular) rotor, performing rotational motions inside the cavity of the complex shape. After the wave of experimental models of cars and motorcycles, which came to the 60s and 70s of the twentieth century, interest in the RPD decreased, although a number of companies continue to work on improving the design of the Vankel engine. Currently, the RPD is equipped with Mazda's passenger cars. Rotary-piston engine finds use in models.
Principle of operation
The power of gases from the burnt fuel-air mixture leads to a rotor, struck through the bearings to the eccentric shaft. The rotor movement relative to the engine housing (stator) is performed after a pair of gears, one of which, larger, is fixed on the inner surface of the rotor, the second, reference, smaller size, is rigidly attached to the inner surface of the engine side cover. The interaction of gears leads to the fact that the rotor performs circular eccentric movements, contacting the edges with the inner surface of the combustion chamber. As a result, three insulated variable volume chambers are formed between the rotor and the engine case, which occur the processes of compression of the fuel-air mixture, its combustion, the expansion of gases that have pressure on the operating surface of the rotor and cleansing the combustion chamber from the exhaust gases. The rotational motion of the rotor is transmitted to the eccentric shaft mounted on the bearings and transmitting the torque on the transmission mechanisms. Thus, two mechanical pairs are simultaneously operating in the RPD: the first is the regulating rotor movement and consisting of a pair of gears; And the second is the transforming circular motion of the rotor in the rotation of the eccentric shaft. The gear ratio of the gear of the rotor and stator 2: 3, so the rotor has time for one complete turnover of the eccentric shaft by 120 degrees. In turn, for one complete turnover of the rotor in each of the three chambers-formed cameras, a full four-stroke cycle of the internal combustion engine is performed.
rPD scheme
1 - inlet window; 2 graduation window; 3 - body; 4 - Camera combustion; 5 - fixed gear; 6 - rotor; 7 - gear wheel; 8 - shaft; 9 - Ignition Candle
Advantages of RPD
The main advantage of the rotor-piston engine is the simplicity of design. The RPD is 35-40 percent less details than in a piston four-stroke engine. In the RPD there are no pistons, connecting rods, crankshaft. In the "classic" version of the RPD there is no gas distribution mechanism. The air mixture enters the engine working cavity through the inlet window, which opens the rotor face. The exhaust gases are thrown through an exhaust window that crosses, again, the rotor face (it resembles the device of the gas distribution of the two-stroke piston engine).
A separate mention deserves a lubricant system, which in the simplest version of the RAP is practically absent. Oil is added to the fuel - as when operating two-stroke motorcycle engines. The grease of friction pairs (primarily the rotor and the working surface of the combustion chamber) is produced by the fuel-air mixture.
Since the mass of the rotor is small and easily balanced by a mass of counterweight eccentric shaft, RPD is characterized by a small level of vibrations and good uniformity of work. In cars with RPD it is easier to balance the engine, having achieved a minimum level of vibrations, which is well affected by the comfort of the machine as a whole. A special smoothness of the course is distinguished by two-engine motors, in which the rotors themselves are decreasing the level of vibration by balance sheets.
Another attractive quality of the RPD is a high specific power at high eccentric tree revolutions. This allows you to achieve from the car with the RPD of excellent speed characteristics with a relatively small fuel consumption. Small inertia of the rotor and increased compared to piston internal combustion engines. Specific power allows you to improve the dynamics of the car.
Finally, the important dignity of the RAP is small sizes. The rotary engine is less than the piston four-stroke motor of the same power is somewhat twice. And this allows rational to use the space of the engine compartment, more accurately calculate the location of the transmission nodes and the load on the front and rear axle.
Disadvantages of RPD
The main disadvantage of the rotary-piston engine is the low efficiency of the gap seals between the rotor and the combustion chamber. The complex form of the RPD rotor requires reliable seals not only on thends (and four of each surface each surface - two by vertex, two on the side of the side), but also on the side surface coming into contact with the engine covers. In this case, the seals are made in the form of spring-loaded strips from high-alloyed steel with particularly accurate processing of both working surfaces and ends. Posted in the design of seals tolerances on the expansion of the metal from heating worsen their characteristics - to avoid the breakthrough of gases in the end sections of the sealing plates is almost impossible (in piston engines, the labyrinth effect is used, installing sealing rings with gaps in different directions).
In recent years, the reliability of seals has increased dramatically. Designers found new materials for seals. However, it is not yet necessary to talk about some kind of breakthrough. Seals still remain the most narrow place of the RAP.
A complex system of rotor seals requires effective lubrication of rubbing surfaces. RPD consumes more oil than a four-stroke piston engine (from 400 grams to 1 kilogram per 1000 kilometers). At the same time, the oil burns along with the fuel, which is badly affected by the environmental friendliness of the motors. In the exhaust gases of the RPD dangerous to the health of people substances more than in the exhaust gases of piston engines.
Special requirements are presented to the quality of oils used in the RAP. This is due, firstly, with a tendency to elevated wear (due to the large area of \u200b\u200bcontacting parts - the rotor and the internal chamber of the engine), secondly, to overheating (again due to increased friction and due to the small size of the engine itself ). For the RPD, the irregular oil change is solurally dangerous - since abrasive particles in the old oil dramatically increase engine wear, and the control of the motor. Starting a cold engine and insufficient heating lead to the fact that in the contact zone of the rotor seals with the surface of the combustion chamber and side lids, there is little lubricant. If the piston engine jars when overheated, then the RPD is most often - during the start of the cold engine (or when driving in cold weather, when cooling is redundant).
In general, the working temperature of the RPD is higher than that of piston engines. Thermal-crimped area is a combustion chamber that has a small volume and, accordingly, an increased temperature, which makes it difficult to the fuel-air mixture (RPD due to the extended combustion chamber, prone to detonation, which can also be attributed to the disadvantages of this type of engines). Hence the demanding RPD to the quality of candles. Usually they are installed in these engines in pairs.
Rotary-piston engines with excellent power and high-speed characteristics are less flexible (or less elastic) than piston. They give out optimal power only at sufficiently high revs, which forces the designers to use the RAP in a pair with multistage CP and complicates the design of automatic transmissions. Ultimately, the RAPs are not as economical as they should be in theory.
Practical application in the automotive industry
The greatest spread of the RPD was obtained in the late 60s and early 70s of the last century, when the patent for the Vankel engine was purchased by 11 leading automakers in the world.
In 1967, the German company NSU released the serial passenger car of the NSU RO 80 business class. This model was produced for 10 years and divided into the world in the amount of 3,7204 copies. The car was popular, but the disadvantages of the RPD installed in it, after all, spoiled the reputation of this wonderful machine. Against the background of durable competitors, the model NSU RO 80 looked "pale" - mileage to the overhaul of the engine at the stated 100 thousand kilometers did not exceed 50 thousand.
Citroen, Mazda, VAZ concern, experimented with RPD. Mazda achieved the greatest success, which released his passenger car from the RAP back in 1963, four years earlier than the appearance of NSU RO 80. Today, the Mazda concern equips the RPD Sports of the RX series. Modern cars Mazda RX-8 are delivered from many shortcomings of the RPD Felix Vankel. They are quite environmentally friendly and reliable, although among car owners and repair professionals are considered "capricious".
Practical application in the motor industry
In the 70s and 80s, some manufacturers of motorcycles were experimed with RPD - Hercules, Suzuki and others. Currently, the petrolery production of "rotary" motorcycles has been established only in the Norton company, which produces the NRV588 model and the NRV700 motorcycle prepare for serial production.
Norton NRV588 - Sportbike equipped with a two-engine motor with a total volume of 588 cubic centimeters and a developing capacity of 170 horsepower. With a dry weight of a motorcycle in 130 kg, the energy-fitness of the sportsbike looks literally to be processed. The engine of this machine is equipped with the inlet path systems of the variable and electronic fuel injection. About the model NRV700 It is only known that the power of the RPD of this sportbike will reach 210 hp.
Definition.
Piston Engine - One of the embodiments of the internal combustion engine, working through the transformation of the internal energy of the combusting fuel into the mechanical operation of the internal movement of the piston. The piston comes in motion when expanding the working fluid in the cylinder.
The crank-connecting mechanism converts the translational movement of the piston into the rotational motion of the crankshaft.
The operating cycle of the engine consists of a sequence of tact of one-sided translational strokes of the piston. The engines with two and four clocks of work are subdivided.
The principle of operation of the two-stroke and four-stroke piston engines.
Number of cylinders B. piston engines It may vary depending on the design (from the 1st to 24). The engine volume is assumed to be equal to the sum of the volumes of all cylinders, the capacity of which is found on the product of the cross section on the stroke of the piston.
AT piston engines Different designs in different ways are the process of fuel ignition:
Electrical dischargewhich is formed on the ignition candlelight. Such engines can operate both on gasoline and other types of fuel (natural gas).
Squeezing of the working body:
AT diesel enginesoperating on diesel fuel or gas (with 5% by the addition of diesel fuel), air is compressed, and when the piston of maximum compression point is reached, the fuel injection occurs, which flammives from contact with heated air.
Engines compression model. The supply of fuel in them is exactly the same as in gasoline engines. Therefore, for their work, a special composition of fuel is needed (with impurities of air and diethyl ether), as well as accurate adjustment of the degree of compression. Compressor engines found their distribution in aircraft and automotive industry.
Kalil engines. The principle of their action is largely similar to the engines of the compression model, but it did not cost without structural features. The role of the ignition in them is performed - a calil candle, the intensity of which is maintained by the energy of the combusting fuel on the previous tact. The composition of the fuel is also special, the basis is taken by methanol, nitromethane and castor oil. Engines are used, both on cars and on airplanes.
Calorizator engines. In these engines, ignition occurs when fuel contact with hot engine parts (usually - the bottom of the piston). Martin gas is used as fuel. They are used as drive engines on rolling mills.
Fuel types used in piston engines:
Liquid fuel - diesel fuel, gasoline, alcohols, biodiesel;
Gaza - natural and biological gases, liquefied gases, hydrogen, gaseous oil cracking products;
Produced in a gas generator from coal, peat and wood, carbon monoxide is also used as fuel.
Work of piston engines.
Engine operation cycles Details are painted in technical thermodynamics. Various cyclics are described by various thermodynamic cycles: Otto, diesel engine, atkinson or miller and trinker.
Causes of breakdowns of piston engines.
PDD piston engine.
Maximum efficiency that managed to get on piston Engine is 60%, i.e. A little less than half of the combusting fuel is spent on the heating of engine parts, and also comes out with heat exhaust gases. In this connection, it has to equip the engine cooling systems.
Classification of cooling systems:
Air S. - Give heat air due to the ribbed outer surface of the cylinders. Lie applied
bo on weak engines (dozens of hp), or on powerful aircraft engines, which are cooled by a rapid flow of air.
Liquid SO - The liquid (water, antifreeze or oil) is used as a cooler, which pumps through the cooling shirt (channels in the cylinder block walls) and enters the cooling radiator in which it is cooled by air flows, natural or fans. Rarely, but a metal sodium is also used as a coolant, which is melted from heat heating engine.
Application.
Piston engines, due to its power range, (1 watt - 75,000 kW) have gained more popularity not only in the automotive industry, but also aircraft and shipbuilding. They are also used to drive combat, agricultural and construction equipment, electric generators, water pumps, chainsaws and other machines, both mobile and stationary.
The most famous and widely used all over the world mechanical devices are internal combustion engines (hereinafter DVS). The range is extensive, and they differ in a number of features, for example, the number of cylinders whose number can vary from 1 to 24 used by the fuel.
Work of the piston internal combustion engine
Single Cylinder DVS It can be considered the most primitive, unbalanced and having an uneven move, despite the fact that it is the starting point in creating multi-cylinder engines of the new generation. To date, they are used in aircraft production, in the production of agricultural, household and garden tools. For automotive industry, four-cylinder engines and more solid devices are massively used.
How does it and what is it?
Piston internal combustion engine It has a complex structure and consists of:
- The case, which includes a block of cylinders, the head of the cylinder block;
- Gas distribution mechanism;
- Crank-connecting mechanism (hereinafter CSM);
- A number of auxiliary systems.
KSM is a link between the energy of the fuel-air mixture released during the combustion of the air mixture (further) in the cylinder and the crankshaft that ensures the movement of the car. The gas distribution system is responsible for gas exchange in the process of functioning of the unit: the access of atmospheric oxygen and the TVS into the engine, and the timely removal of gases formed during the combustion.
The device of the simplest piston engine
Auxiliary systems are presented:
- Inlet, providing oxygen in the engine;
- Fuel represented by fuel injection system;
- Ignition providing a spark and ignition of fuel assemblies for gasoline engines (diesel engines are characterized by self-ignition of a mixture of high temperature);
- Lubrication system, which reduces the friction and wear of contacting metal parts using machine oil;
- Cooling system that does not allow overheating of engine parts, ensuring the circulation of special Tosol type liquids;
- A graduation system that reduces gases into the corresponding mechanism consisting of exhaust valves;
- The control system that monitors the functioning of the engine at the electronics level.
The main work element in the described node is considered piston internal combustion enginewhich itself is the team detail.
DVS piston device
Step-by-step scheme of operation
The work of the DVS is based on the energy of expanding gases. They are the result of the combustion of the TVS inside the mechanism. This physical process forces the piston to move in the cylinder. Fuel in this case can serve:
- Liquids (gasoline, dt);
- Gases;
- Carbon monoxide as a result of burning solid fuel.
Engine operation is a continuous closed cycle consisting of a certain number of clocks. The most common in 2 types of two types of clocks are most common:
- Two-stroke, compression and workforce;
- Four-stroke - characterized by four equal stages in the duration: inlet, compression, work move, and the final release, this indicates a fourfold change in the position of the main working element.
The start of the tact is determined by the location of the piston directly in the cylinder:
- Top dead dot (hereinafter NTC);
- Lower dead dot (Next NMT).
Studying the algorithm of the four-stroke sample, you can thoroughly understand principle of engine engine.
Principle of engine engine
The inlet occurs by passing out of the upper dead point through the entire cavity of the working piston cylinder with simultaneous tvs. Based on structural features, mixing incoming gases can occur:
- In the intake system manifold, it is relevant if the engine is gasoline with distributed or central injection;
- In the combustion chamber, if we are talking about a diesel engine, as well as an engine running on gasoline, but with direct injection.
First Takt. It passes with open valves of the gas distribution mechanism. The number of intake and release valves, their stay in the open position, their size and wear state are factors affecting the engine power. The piston at the initial stage of compression is placed in NMT. Subsequently, it begins to move up and compress the accumulated TVx to the sizes defined by the combustion chamber. The combustion chamber is free space in the cylinder, remaining between its top and piston in the upper dead point.
Second tact It assumes the closure of all engine valves. The density of their adjustment directly affects the quality of the compression of the FVS and its subsequent fire. Also on the quality of compression of the fuel assembly, the level of wear of components of the engine has a great influence. It is expressed in the size of the space between the piston and the cylinder, in the density of the valve adjacent. The engine compression level is the main factor affecting its power. It is measured by a special compressometer device.
Working Begins when the process is connected Ignition systemgenerating a spark. The piston is at the maximum top position. The mixture explodes, gases that create increased pressure are distinguished, and the piston is driven. The crank-connecting mechanism in turn activates the rotation of the crankshaft, which ensures the movement of the car. All system valves at this time are in a closed position.
Graduation tact It is completing in the cycle under consideration. All exhaust valves are in the open position, allowing the engine to "exhale" the combustion products. The piston returns to the starting point and is ready for the beginning of the new cycle. This movement contributes to the exhaust system, and then to the environment, exhaust gases.
Scheme of the engine of internal combustionAs mentioned above, based on cyclicity. Examined in detail how the piston engine works, It can be summarized that the efficiency of such a mechanism is not more than 60%. It is determined by such a percentage in that in a separate time, the working clock is performed only in one cylinder.
Not all the energy obtained at this time is directed to the movement of the car. Part it is spent on maintaining the flywheel movement, which inertia provides the operation of the car during three other clocks.
A certain amount of thermal energy is involuntarily spent on the heating of the housing and the exhaust gases. That is why the engine capacity of the car is determined by the number of cylinders, and as a result, the so-called engine volume calculated according to a certain formula as the total volume of all operating cylinders.
When burning fuel, thermal energy is distinguished. The engine in which the fuel combines directly inside the working cylinder and the energy of the gases obtained at the same time is perceived by the piston moving in the cylinder, refer to the piston.
So, as already mentioned earlier, the engine of this type is the main for modern cars.
In such engines, the combustion chamber is placed in a cylinder in which the thermal energy from the combustion of the fuel and air mixture is converted into the mechanical energy of the piston moving progressively and then the special mechanism called the crank shaft is converted into the rotational energy of the crankshaft.
At the place of formation of a mixture consisting of air and fuel (combustion), piston engineers are divided into engines with an external and internal conversion.
At the same time, the engines with external mixture formation by the nature of the fuel used are divided into carburetor and injection, operating on light liquid fuel (gasoline) and gas-operating gas (gas generator, luminous, natural gas, etc.). Engines with compression ignition are diesel engines (diesel engines). They operate on heavy liquid fuel (diesel fuel). In general, the design of the engines themselves is almost the same.
The operating cycle of four-stroke engines in the piston performance is performed when the crankshaft makes two turns. By definition, it consists of four separate processes (or clocks): inlet (1 tact), compression of the fuel and air mixture (2 tact), working stroke (3 tact) and exhaust gases (4 tact).
The shift of the engine work clocks is provided with a gas distribution mechanism consisting of a camshaft, a transfer system of pushers and valves, insulating the working space of the cylinder from the external environment and mainly ensure the shift of the phases of gas distribution. Due to the inertia of gases (singularities of gas-dynamics processes), the intake and release clocks for the real engine overlap, which means their joint action. At high speed, the overlap of the phases affects the engine at work. On the contrary, than it is more on low revs, the smaller the engine torque. This phenomenon is taken into account in the work of modern engines. Create devices to change the phases of gas distribution during operation. There are various designs of such devices most suitable of which are electromagnetic devices for adjusting the phases of gas distribution mechanisms (BMW, Mazda).
Carburetor DVS
In carburetor engines, the fuel-air mixture is prepared before its entry into the engine cylinders, in a special device in the carburetor. In such engines, a combustible mixture (a mixture of fuel and air) entered the cylinders and mixed with the remnants of the exhaust gases (working mixture) flammifies from an extraneous energy source - the electrical spark of the ignition system.
Injector DVS
In such engines, due to the presence of spraying nozzles, carrying out gasoline injection into the intake manifold, mixing with air.
Gas economy
In these engines, the gas pressure after exiting the gas gearbox is greatly reduced and brought to close atmospheric, after which, with the help of an air-gas mixer, it is absorbed by electrical injectors (similar to injection engines) in the intake manifold engine.
The ignition, as in the previous types of engines, is carried out from the spark of the candle slipsing between its electrodes.
Diesel DVS
In diesel engines, the mixing formation occurs directly inside the engine cylinders. Air and fuel enroll in cylinders separately.
At the same time, at first, only the air comes into the cylinders, it is compressed, and at the time of its maximum compression, the jet of fine fuel through a special nozzle is injected into the cylinder (the pressure inside the cylinders of such engines reaches much greater values \u200b\u200bthan in the previous type engines), the inflammation of the formed Mixtures.
In this case, the ignition of the mixture occurs as a result of an increase in air temperature in its strong compression in the cylinder.
Among the disadvantages of diesel engines, it is possible to highlight higher, compared to previous types of piston engines - the mechanical tension of its parts, in particular the crank-connecting mechanism, requiring improved strength qualities and, as a result, large dimensions, weight and cost. It increases due to the complicated design of the 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 exhaust gases due to heterogeneous combustion of the working mixture inside the cylinders.
Gasiodialistics
The principle of operation of such an engine is similar to the operation of any of the varieties of gas engines.
The fuel and air mixture is prepared according to a similar principle by supplying gas to an air-gas mixer or in the intake manifold.
However, the mixture is ignited by the replacement portion of diesel fuel injected into the cylinder by analogy with the operation of diesel engines, and not using an electrical candle.
Rotary-piston DVS
In addition to the established name, this engine has the name by the name of the inventor who created his inventor and is called the Vankel engine. Offered at the beginning of the 20th century. Currently, manufacturers of Mazda RX-8 are engaged in such engines.
The main part of the engine forms a triangular rotor (piston analog), rotating in a specific form chamber, according to the design of the inner surface, resembling the number "8". This rotor performs the function of the piston of the crankshaft and the gas distribution mechanism, thus eliminating the gas distribution system, mandatory for piston engines. It performs three full working cycles for one of its turnover, which allows one such engine to replace the six-cylinder piston engine. Despite a lot of positive qualities, among which also the fundamental simplicity of its design, has disadvantages that impede its widespread use. They are associated with the creation of durable reliable chamber seals with a rotor and the construction of the necessary engine lubrication system. The working cycle of rotary-piston engines consists of four clocks: the intake of the fuel-air mixture (1 tact), compression of the mixture (2 tact), expansion of the combusting mixture (3 tact), release (4 tact).
Rotary-Bad DVS
This is the same engine that is applied in E-mobile.
Gas turbine DVS
Already today, these engines are successfully able to replace the piston engine in cars. And although the degree of perfection design of these engines reached only in the past few years, the idea of \u200b\u200bapplying gas turbine engines in cars has arisen a long time ago. 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 their production techniques.
What does the gas turbine engine represent? To do this, let's look at its principal scheme.
Compressor (post9) and gas turbine (pos. 7) are on the same shaft (pos.8). The shaft of the gas turbine rotates in the bearings (pos.10). The compressor takes the air from the atmosphere, compresses it and sends to the combustion chamber (pos.3). The fuel pump (pos.1) is also driven from the turbine shaft. It serves fuel to the nozzle (pos.2), which is installed in the combustion chamber. Gaseous combustion products come through the guide apparatus (pos.4) of the gas turbine on the blade of its impeller (pos.5) and cause it to rotate in a given direction. The spent gases are produced into the atmosphere through the nozzle (pos.6).
And although this engine is full of flaws, they are gradually eliminated by design. At the same time, compared with piston DVS, gas turbine DVS has a number of significant advantages. First of all, it should be noted that as a steam turbine, gas can develop large revs. Which allows you to get high power from smaller in size and lighter by weight (almost 10 times). In addition, the only type of movement in the gas turbine is rotational. At the piston engine, in addition to the rotational, there are reciprocating movements of pistons and complex movements of rods. Also gas turbine engines do not require special cooling systems, lubricants. The absence of significant friction surfaces with a minimal amount of bearings provide long-term operation and high reliability of the gas turbine engine. Finally, it is important to note that the power is carried out using kerosene or diesel fuel, i.e. Cheaper species than gasoline. Holding the development of automotive gas turbine engines The reason is the need for artificial limiting the temperature of the gas turbines entering the blades, since there are still very roads high-state metals. 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 freight engines, the gas temperature has to be limited to the limits of 700 ° C, and in aircraft engines up to 900 ° C. Modako, there are already some ways to increase the efficiency of these engines by removing the warmth of the exhaust gases to heal the air combustion chamber. The solution to the problem of creating a highly economical automobile gas turbine engine largely depends on the success of work in this area.
Combined DVS
A great contribution to the theoretical aspects of the work and the creation of combined engines was introduced by an engineer of the USSR, Professor A.N. Schest.
Alexey Nesterovich Shelest
These engines are a combination of two machines: piston and shovel, which can act as a turbine or compressor. Both of these machines are important elements of the workflow. As an example of such an engine with gas turbine superior. In this case, in the usual piston engine, with the help of a turbocharger, a coercive air supply to the cylinders occurs, which allows you to increase the power of the engine. It is based on the use of exhaust gas flow energy. It affects the impeller of the turbine, fixed on the shaft on the one hand. And spins it. On the same shaft, on the other hand, the blades of the compressor are located. Thus, with the help of the compressor, the air is injected into the engine cylinders due to the vacuum in the chamber on one side and forced air supply, on the other hand, a large amount of air and fuel mixture comes into the engine. As a result, the volume of combustable fuel increases and the gas formed as a result of this combustion takes longer volumes, which creates greater power on the piston.
Two-stroke
This is referred to as the OI with an unusual gas distribution system. It is implemented in the process of passing the piston making reciprocating movements, two pipes: intake and graduation. You can meet his foreign designation "RCV".
Engine work processes are performed during one crankshaft turnover and two piston strokes. The principle of work is as follows. First, the cylinder is purned, which means the inlet of a combustible mixture with simultaneous intake of exhaust gases. Then there is a compression of the working mixture, at the time of the rotation of the crankshaft by 20--30 degrees from the position of the corresponding NMT when moving to the VMT. And the working stroke, the length of the piston stroke from the upper dead point (VTT) without reaching the lower dead point (NMT) by 20--30 degrees on the crankshaft revolutions.
There are obvious shortcomings of two-stroke engines. Firstly, the faint of the two-stroke cycle is the blowing of the engine (again with t. Gas dynamics). This happens on the one hand due to the fact that, the separation of fresh charge from exhaust gases is impossible, i.e. Inevitable losses in the essence of a fresh mixture flying into the exhaust pipe, (or the air is about the diesel). On the other hand, the work move lasts less than half of the turnover, which is already talking about the decline in the efficiency of the engine. Finally the duration of an extremely important gas exchange process, in a four-stroke engine occupying half of the working cycle, cannot be increased.
Two-stroke engines are more complicated and more expensive at the expense of the mandatory use of the purge system or the supervision system. There is no doubt that the increased thermal tension of the details of the cylindroport group requires the use of more expensive materials of individual parts: pistons, rings, cylinder sleeves. Also, performing the piston of gas distribution functions imposes a limit on its height size consisting of the height of the piston stroke and the height of the windows for purge. It is not as critical in the moped, but significantly weights the piston when installing it on vehicles requiring significant power costs. Thus, when the power is measured dozens, or even hundreds of horsepower, the increase in the weight of the piston is very noticeable.
Nevertheless, certain works were carried out towards improving such engines. In the Ricardo engines, special distribution sleeves were introduced with a vertical move, which was a certain attempt to make a possible reduction in the dimensions and weight of the piston. The system turned out to be quite complicated and very expensive in performance, so such engines were used only in aviation. It is necessary to additionally notice that there are twice as high heat-stress exhaust valves (with a directing valve purge) in comparison with the four-stroke engines valves. In addition, there are a longer direct contact with the spent gases, and therefore the worst heat sink.
Six-contact economy
The basis of the work is based on the principle of operation of the four-stroke engine. Additionally, its designs have elements that, on the one hand, increase its efficiency, while on the other hand reduce its loss. There are two different types of such engines.
In engines operating on the basis of OTO cycles and diesel, there are significant heat losses during fuel combustion. These losses are used in the engine of the first design as an additional power. In the designs of such engines additionally fuel-air mixture, pairs or air are used as a working medium for an additional piston running, as a result of which the power increases. In such 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:
engine Bayulas (from English. Bajulaz). Baulas (Switzerland) was created;
engine Crowera (from English Crower). Invented by Bruce Croweer (USA);
Bruce Croweer
The engine engine (from the English. Velozeta) was built in an engineering college (India).
The principle of operation of the second type of engine is based on the use of an additional piston in its design on each cylinder and located opposite the main one. The additional piston moves with a reduced twice with respect to the main piston frequency, which provides for each cycle six pistons. Additional piston in its primary purpose replaces the traditional gas distribution mechanism of the engine. The second function consists in increasing the degree of compression.
The main, independently created constructions of such engines two:
engine Bir HED (from English Beare Head). Invented Malcolm Bir (Australia);
engine with the name "Charged Pump" (from English. German Charge Pump). Invented Helmut Kotman (Germany).
What will be in the near future with the internal combustion engine?
In addition to the flaws specified at the beginning of the article, there is another principal disadvantage of not allowing the use of DVS separately from the car transmission. The power unit of the car is formed by the engine together with the car transmission. It allows you to move the car at all necessary speeds. But separately taken in DVS develops the highest power only in the narrow range of revolutions. This is the actually why the transmission is necessary. Only in exceptional cases cost without transmission. For example, in some plane structures.
Piston DVSs found the wider distribution as energy sources on automobile, railway and sea transport, in agricultural and construction industries (tractors, bulldozers), in emergency energy systems of special objects (hospitals, communication lines, etc.) and in many others regions of human activity. In recent years, mini-CHP based on gas pipelines, with the help of which the tasks of the energy supply of small residential areas or industries are effectively solved. The independence of such CHPs from centralized systems (type RAO UES) improves the reliability and stability of their functioning.
Extremely diverse piston engineers are capable of providing a very wide capacity interval - from very small (engine for aircraft models) to very large (engine for ocean tankers).
With the basics of the device and the principle of the actions of the piston DVS, we have repeatedly acquainted, ranging from the school course of physics and ending with the course "Technical thermodynamics". And yet, to secure and deepen the knowledge, consider it very briefly once again this question.
In fig. 6.1 shows the engine device diagram. As you know, burning fuel in the engine is carried out directly in the working body. In piston engine, such burning is carried out in the working cylinder 1 with the piston moving in it 6. The flue gases resulting as a result of combustion pushed the piston, forcing it to make a useful work. The progressive movement of the piston with a connecting roddle 7 and the crankshaft 9 is converted into a rotational, more convenient for use. The crankshaft is located in the crankcase, and the engine cylinders - in another case part, called a block (or shirt) of cylinders 2. In the cylinder lid 5 are intake 3 and graduation 4 Valves with a forced cam drive from a special distributor, kinematically associated with a crankshaft machine.
Fig. 6.1.
In order for the engine to work continuously, it is necessary to periodically remove the combustion products from the cylinder and fill it with new portions of fuel and oxidizing agent (air), which is carried out due to the movements of the piston and valve operation.
Piston DVS is customary to classify according to various general features.
- 1. According to the method of mixing, ignition and heat supply, the engines are divided into machines with forced ignition and with self-ignition (carburetor or injection and diesel).
- 2. On the organization of the workflow - on four-stroke and two-strokes. In the last workflow, the workflow is made not for four, and for the two stroke of the piston. In turn, the two-stroke engine is divided into machines with a straight-flow valve-slit purge, with a crank-chamber blowing, with a straight-flow purge and oppositely moving pistons, etc.
- 3. For its intended purpose - to stationary, ship, diesel, automotive, autotractor, etc.
- 4. In terms of speed - on low-speed (up to 200 rpm) and high-speed.
- 5. For average piston velocity y\u003e n \u003d? p / 30 - on low-speed and high-speed (s? "\u003e 9 m / s).
- 6. According to the pressure of the air at the beginning of the compression - on ordinary and superimposed using drive blowers.
- 7. On the use of heat of exhaust gases - to ordinary (without using this heat), with turbocharging and combined. In machines with turbocharging, the exhaust valves open a little earlier than usual and flue gases with higher pressure than usually, sent to a pulsed turbine, which drives the turbocharger supplying air to the cylinders. This allows you to burn more fuel in the cylinder, improving the efficiency, and the technical characteristics of the machine. In combined internal combustion engine, the piston part serves in a large gas generator and produces only ~ 50-60% of the machine power. The rest of the total capacity is obtained from a gas turbine operating on flue gases. For this flue gases at high pressure r And temperature / are directed to the turbine, the shaft of which, using a toothed transmission or hydromeflua, transmits the obtained power of the main set of installation.
- 8. In terms of the number and location of cylinders, the engines are: single, two- and multi-cylinder, row, k-shaped ,.t-shaped.
We now consider the real process of a modern four-stroke diesel. It is called a four-stroke, because the full cycle is carried out here for four full piston moves, although, as we now see, during this time there are several more real thermodynamic processes. These processes are clearly represented in Fig. 6.2.
Fig. 6.2.
I - suction; II - compression; III - work move; IV - Poverty
During takta suction (1) Suction (intake) The valve opens in several degrees to the top of the dead point (VTT). The point of opening corresponds to the point g. on the r- ^ -Diagram. In this case, the suction process occurs when the piston moves to the lower dead point (NMT) and goes for pressure r NS. less atmospheric /; A (or pressurization pressure r). With a change in the direction of the movement of the piston (from NMT to NTC), the intake valve is also not immediately closed, but with a certain delay (at the point t.). Next, with the valves closed, the working fluorescence is compressed (to the point with). In diesel engines, clean air is absorbed and compressed, and in the carburetulator - a working mixture of air with gasoline pairs. This piston move is customary to call compression (Ii).
For several degrees, the angle of rotation of the crankshaft to the VMT into the cylinder is injected through the nozzle diesel fuel, its self-ignition, combustion and expansion of combustion products occurs. In the carburetor machines, the working mixture is enhanced by electrical spark discharge.
When compressing air and a relatively small heat exchange with walls, its temperature is significantly increased, exceeding the temperature of self-ignition fuel. Therefore, injected finely sprayed fuel warms very quickly, evaporates and lights up. As a result of the combustion of the fuel, the pressure in the cylinder first sharply, and then, when the piston starts its way to NMT, with a decreasing pace increases to a maximum, and then as the last portions of the fuel arrived during the injection, even begins to decrease (due to intensive growth cylinder volume). We will consider conditionally that at the point with" The burning process ends. Next, the process of expanding flue gases is followed, when the power of their pressure moves the piston to NMT. The third stroke of the piston, including the processes of combustion and expansion, is called workforce (Iii), for only at this time the engine makes a useful work. This work accumulate with the help of the flywheel and give to the consumer. Part of the accumulated work is consumed when performing the other three clocks.
When the piston is approaching NMT, the exhaust valve opens with some advance (point B) And the exhaust flue gases rush into the exhaust pipe, and the pressure in the cylinder drops almost to atmospheric. During the piston, the flue gases from the cylinder occurs from the cylinder (IV - pushing). Since the exhaust tract of the engine has a certain hydraulic resistance, the pressure in the cylinder during this process remains above atmospheric. The exhaust valve closes later the passage of the NTT (point p),gAK that in each cycle there is a situation where both intake and exhaust valves are both open and the exhaust valve (they say about the overlap of valves). This allows you to better clean the working cylinder from the combustion products, the effectiveness and completeness of the combustion of fuel increases as a result.
A different cycle of two-stroke machines is organized (Fig. 6.3). Usually these are supervised engines, and for this they, as a rule, have a drive blower or turbocharger 2 which drums the air into the air receiver during operation 8.
The two-stroke engine cylinder always has purge windows 9, through which air from the receiver enters the cylinder when the piston, passing to the NCT, will start opening them more and more.
For the first stroke of the piston, which is customary to be called a workforce, in the cylinder of the engine is combustion of injected fuel and expansion of combustion products. These processes on the indicator diagram (Fig. 6.3, but) Reflected Liniya c - I - t. At point t.exhaust valves open and under the action of overpressure, flue gases are rushed into the graduation path 6, in the result
Fig. 6.3.
1 - suction nozzle; 2 - blower (or turbocharger); 3 - piston; 4 - exhaust valves; 5 - nozzle; 6 - graduation tract; 7 - worker
cylinder; 8 - air receiver; 9- blowing windows
tATE The pressure in the cylinder falls noticeably (point p). When the piston descends so much that the purge windows begin to open, compressed air from the receiver rushes into the cylinder 8 , pushing out the remains of flue gases from the cylinder. In this case, the working volume continues to increase, and the pressure in the cylinder decreases almost to the pressure in the receiver.
When the direction of the piston movement changes to the opposite, the process of purging the cylinder continues until the blowing windows remain at least partially open. At point to(Fig. 6.3, b) The piston completely overlaps the blowing windows and the compression of the next portion of the air that has fallen into the cylinder begins. In a few degrees to VTT (at the point with") The fuel injection begins through the nozzle, and then the previously described processes leading to ignition and fuel combustion.
In fig. 6.4 Schemes explaining the structural device of other types of two-stroke engines. In general, the duty cycle in all of these machines is similar to the described, and constructive features are largely affected only on the duration.
Fig. 6.4.
but - looped slit purge; 6 - Direct-time purge with oppositely moving pistons; at - crank-chamber purge
individual processes and, as a result, at the technical and economic characteristics of the engine.
In conclusion, it should be noted that the two-stroke engines are theoretically allowed, with other things being equal, to obtain twice as high power, but in reality due to the worst conditions for cleaning the cylinder and relatively large internal losses, this win is somewhat less.
