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the classification of engines in the first section ............................................. 3
the overall structure of engines in the second section ....................... 4
the working principle of four-stroke engines in the third section ............ Sex .................................. 13
Thanks ................................... 16
References .................... This paper gives a detailed explanation of the engine, including the classification, structure and working principle of the engine, and analyzes the performance and main indexes of the automobile engine accordingly.
Keywords: two-stroke and four-stroke performance index characteristics of gasoline engine diesel engine
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Classification of engines in the first section
An engine is a machine that directly converts some energy in nature into mechanical energy and drags some machinery to work. An engine that converts heat energy into mechanical energy is called a heat engine (heat engine for short), in which heat energy is generated by fuel combustion. Internal combustion engine is a kind of heat engine, which is characterized in that liquid or gas fuel is mixed with air and directly input into the machine for combustion to generate heat energy, and then converted into mechanical energy. Another kind of heat engine is an external combustion engine, such as a steam engine, a steam turbine or a gas turbine. Its characteristic is that fuel burns outside the machine to heat water, generating high-temperature and high-pressure steam, which is transported to the inside of the machine, so that the contained heat energy is converted into mechanical energy.
compared with external combustion engines, internal combustion engines have the advantages of high thermal efficiency, small volume, light weight, easy movement and good starting performance, so they are widely used in airplanes, ships, automobiles, tractors, tanks and other vehicles. However, internal combustion engines generally require the use of petroleum fuel, and the exhaust gas contains high harmful gas components. In order to solve the problems of energy and air pollution, the research and development of exhaust purification and other new energy engines are being devoted at home and abroad.
according to the different forms of main components that convert thermal energy into mechanical energy, automotive internal combustion engines can be divided into two categories: piston internal combustion engines and gas turbines. The former can be divided into reciprocating piston and rotary piston according to different piston motion modes. Reciprocating piston internal combustion engine is the most widely used in automobiles, which is the main object of this paper. Automobile engines (piston internal combustion engines for automobiles) can be classified according to different characteristics:
(1) According to the ignition mode, they can be divided into compression ignition engines and ignition engines. Compression ignition engine is an internal combustion engine that compresses the air or combustible mixture in the cylinder, produces high temperature and causes fuel to catch fire; Ignition engine is an internal combustion engine that compresses the combustible mixture in the cylinder and ignites it with an igniter.
(2) According to the types of fuel used, it can be divided into gasoline engine, diesel engine, gas fuel engine, gas engine, liquefied petroleum gas engine and multi-fuel engine.
(3) According to the cooling mode, it can be divided into water-cooled and air-cooled engines. Water-cooled engine with water or coolant as cooling medium; Air-cooled engine with air as cooling medium.
(4) According to the intake state, it can be divided into non-supercharged (or naturally aspirated) and supercharged engines. Non-supercharged engines are engines in which the air or combustible mixture before entering the cylinder is not compressed by a compressor, and two-stroke engines with only a scavenging pump and no supercharger also belong to this category; A supercharged engine is an engine in which the air or combustible mixture before entering the cylinder has been compressed in the compressor to increase the charge density.
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(5) According to the number of strokes, it can be divided into two-stroke and four-stroke engines. In the engine, every time the heat energy is converted into mechanical energy, it must go through a series of continuous processes, such as absorbing fresh charge (air or combustible mixture), compressing (inputting fuel when the fresh charge is air), making it ignite and burn to expand to do work, and then discharging the generated exhaust gas from the cylinder, which is called a working cycle. Reciprocating piston engine can be classified according to the number of piston strokes required for each working cycle. Where the piston reciprocates four times (or the crankshaft rotates two times) to complete a working cycle, it is called a four-stroke engine; A two-stroke engine is one in which the piston reciprocates two times (or the crankshaft rotates once) to complete a working cycle.
(6) According to the number and arrangement of cylinders, a single cylinder engine is called, and a multi-cylinder engine with more than two cylinders is called; According to the cylinder center line perpendicular to the horizontal plane, engines that are at a certain angle and parallel are called vertical, oblique and horizontal engines respectively; According to the arrangement of cylinders, multi-cylinder engines can be divided into in-line (cylinders are arranged in one row) and opposed (cylinders are arranged in two rows, and the center line between the two rows is 18). ) and V-shaped engines (the cylinders are arranged in a curved row, and the included angle between two rows of cylinders is V-shaped).
the overall structure of the engine in the second quarter
the engine is a complex machine composed of many mechanisms and systems. There are many structural forms of modern automobile engines, even the same type of engines have various specific structures. We can analyze the overall structure of the engine through some typical structural examples of automobile engines.
taking CA488Q gasoline engine for CA114 series light trucks as an example, the general structure of four-stroke chopper is introduced (fig. 1-1).
(1) engine block the engine block of CA488Q engine includes cylinder head 14, cylinder block 7 and oil pan 37. Some engines divide the cylinder block into two parts, the upper part is called the cylinder block and the lower part is called the crankcase. The engine block serves as the assembly matrix of engine mechanisms and systems, and many parts of it are components of crank-connecting rod mechanism, valve train, supply system, cooling system and lubrication system respectively. The cylinder head and the inner wall of the cylinder block form a part of the combustion chamber, and they are parts that bear high temperature and high pressure. In structural analysis, the engine block is often included in the crank-connecting rod mechanism.
(2) Crank-connecting rod mechanism The crank-connecting rod mechanism includes piston 13, connecting rod 1, crankshaft 5 with flywheel 28, etc. It is a mechanism that changes the linear reciprocating motion of piston into the rotary motion of crankshaft and outputs power.
(3) Valve train The valve train includes intake valve 19, exhaust valve 15, rocker arm 45, valve lash adjuster 46, camshaft 25 and camshaft timing pulley 2 (driven by crankshaft timing pulley 6). Its function is to fill the combustible mixture into the cylinder in time and discharge the exhaust gas from the cylinder in time.
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Figure 2-1 Structure of Jiefang CA488Q gasoline engine
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(4) Supply system The supply system includes a gasoline tank, a gasoline pump, a gasoline filter, a carburetor 38, an air filter, an intake pipe 39, an exhaust pipe 53 and an exhaust muffler. Its function is to mix gasoline and air into a combustible mixture with appropriate composition and supply it to the cylinder for combustion, and exhaust the exhaust gas generated by combustion from the engine.
(5) The function of the ignition system is to ensure that the compressed mixture in the cylinder is ignited in time according to the specified time. These include batteries and generators that supply low-voltage current, as well as distributors, ignition coils and spark plugs.
(6) cooling system the cooling system mainly includes a water pump, a radiator, a fan 22, a water distribution pipe, and a water jacket cast in the cylinder block and the cylinder head. Its function is to dissipate the heat of the heated parts into the atmosphere to ensure the normal operation of the engine.
(7) Lubrication system The lubrication system includes an oil pump 5, an oil filter 51, a pressure-limiting valve, a lubricating oil passage, an oil filter, etc., and its function is to supply lubricating oil to parts that move relatively, so as to reduce the friction resistance between them, reduce the wear of parts, and partially cool the friction parts and clean the friction surfaces.
(8) The starting system includes the starter and its accessories, which are used to start the stationary engine and turn it into self-running.
automotive gasoline engines are generally composed of the above two mechanisms and five systems.
working principle of four-stroke engine in the third quarter
working principle of one-stroke and four-stroke gasoline engines
the structure of modern gasoline engines is shown in figure 3-1. A piston 1 is installed in the cylinder, and the piston is connected with a crankshaft 12 through a piston pin and a connecting rod 11. The piston moves back and forth in the cylinder and drives the crankshaft to rotate through the connecting rod. In order to inhale fresh charge and exhaust waste gas, there are air intake and exhaust systems.
figure 3-2 shows the schematic diagram of the engine. When the piston reciprocates, the position of the transition point at which its top surface changes from one direction to the opposite direction is called the dead point. The stop point when the piston top surface is farthest from the crankshaft center line is called TDC (top dead center); The stop point when the top surface of the piston is closest to the center line of the crankshaft is called the bottom dead center (BDC), and the distance s between the upper and lower stop points of the piston operation is called the piston stroke. The vertical distance from the connecting center of the crankshaft and the lower end of the connecting rod to the center of the crankshaft is called the crank radius. For an engine where the cylinder centerline intersects the crankshaft centerline, the piston stroke 5 is equal to twice the crank radius r.
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The working cycle of a four-stroke engine includes four piston strokes: intake stroke, compression stroke, power stroke and exhaust stroke.
(1) The intake stroke gasoline engine mixes air and fuel in the carburetor outside the cylinder, at the throttle body or in the intake port to form a combustible mixture, which is then sucked into the cylinder.
during intake, the intake valve is opened and the throttle valve is closed. As the piston moves from the top dead center to the bottom dead center, the volume of the cylinder above the piston becomes larger, and the pressure in the cylinder will be below atmospheric pressure, that is, a vacuum degree will be formed in the cylinder. In this way, the combustible mixture is sucked into the cylinder through the intake valve. Due to the resistance of the intake system, the gas pressure in the cylinder at the end of intake is about .75～.9Mpa.
(2) compression stroke In order to make the combustible mixture sucked into the cylinder burn rapidly, so as to generate greater pressure and engine power, it is necessary to compress the combustible mixture before combustion, so as to reduce its volume, increase its density and increase its temperature, so a compression process is needed. In this process, the intake and exhaust valves are all closed, and the crankshaft pushes the piston to move from the bottom dead center to the top dead center for a stroke, which is called compression stroke. When the piston reaches the top dead center, the compression ends. At this time, the mixture is compressed into a small space above the piston, that is, the combustion chamber. The pressure of combustible mixture increases to .6 ~ 1.2 MPa, and the temperature can reach 6 ~ 7 K.
the ratio of the maximum volume of gas in the cylinder before compression to the minimum volume after compression is called compression ratio.
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The compression ratio of modern gasoline engines is generally 6 ~ 9 (some cars reach 9 ~ 11). For example, the compression ratio of EA827 1.6L engine of FAW-Volkswagen Jetta car is 8.5, while the compression ratio of EA113 1.6L engine is 9.3.
the greater the compression ratio, the higher the pressure and temperature of the mixture at the end of compression, and the faster the combustion speed, so the power generated by the engine increases, the thermal efficiency improves and the economy is better. However, when the compression ratio is too large, not only can the combustion situation not be further improved, but abnormal combustion phenomena such as deflagration and surface ignition will appear. Deflagration is an abnormal combustion caused by excessive gas pressure and temperature and spontaneous combustion of combustible mixture at the end far from the ignition center in the combustion chamber. During deflagration, the flame propagates at a very high speed, and the temperature and pressure rise sharply, forming a pressure wave and advancing at the speed of sound. When this pressure wave hits the combustion chamber wall, it makes a sharp knocking sound. At the same time, it will also cause a series of adverse consequences such as engine overheating, power decline and fuel consumption increase. Serious deflagration may even cause valve burning, bearing bush cracking, piston top burning, spark plug insulator breakdown and other mechanical damage phenomena. Surface ignition is another abnormal combustion phenomenon caused by the hot surface in the combustion chamber (such as exhaust valve head, spark plug electrode and carbon deposit) igniting the mixed gas. When surface ignition occurs, it is accompanied by a strong knocking sound (dull), which will increase the mechanical load borne by engine parts and reduce the service life. Therefore, while improving the compression ratio of the engine, we must pay attention to prevent the occurrence of deflagration and surface ignition. In addition, the improvement of engine compression ratio is also limited by exhaust pollution regulations.
(3) Power stroke During this stroke, the intake and exhaust valves are still closed. When the piston approaches the top dead center, the cremation plug installed on the cylinder block (or cylinder head) emits an electric spark to ignite the compressed combustible mixture. After the combustible mixture is burned, a lot of heat energy is released, and its pressure and temperature increase rapidly. The highest pressure P that can be reached is about 3 ~ 5 MPa, and the corresponding temperature is 22～28K K. The high-temperature and high-pressure gas pushes the piston to move from the top dead center to the F dead center, and the crankshaft rotates through the connecting rod and outputs mechanical energy. It is used to keep the engine running, and the rest is used to do external work.
(4) The waste gas generated after the combustion of combustible mixture in the exhaust stroke must be removed from the cylinder for the next working cycle.
when the expansion is near the end, the exhaust valve opens, and the exhaust gas is freely exhausted by the pressure of the exhaust gas. When the piston reaches the bottom dead center and moves to the top dead center, it will continue to forcibly exhaust the exhaust gas to the atmosphere. When the piston reaches the top dead center, the exhaust stroke ends.
Because the combustion chamber occupies a certain volume, it is impossible to exhaust the exhaust gas at the end of exhaust. The exhaust gas left by this part
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is called residual exhaust gas.
to sum up, a four-stroke gasoline engine completes a working cycle through four strokes of intake, compression, combustion work and exhaust. In this issue, the piston reciprocated for four strokes between the upper and lower dead centers, and the crankshaft rotated for two weeks.
working principle of two-stroke and four-stroke diesel engines
the structure of modern diesel engines is shown in figure 3-3.
every working cycle of a four-stroke diesel engine (compression ignition engine) also goes through four strokes: intake, compression, power work and exhaust. But because the fuel of diesel engine is diesel, its viscosity is greater than gasoline, and its self