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catalogue

Section 1 Classification of engines

The overall structure of the engine in the second quarter

Working principle of four-stroke engine in the third quarter

Section 4 Working principle of two-stroke engine 10.

Section 5 Main performance indexes and characteristics of engines .......................................................................................................................................................................

Thank you ............................................. 16.

Refer to ............................ 17.

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Talking about automobile engine

Abstract: At present, reciprocating piston internal combustion engines are widely used in automobiles, and the engine is the heart of automobiles. It is famous for its high thermal efficiency, compact structure, strong maneuverability and simple mobile maintenance. In this paper, the engine is described in detail, including the classification, structure and working principle of the engine, and the performance and main indexes of the automobile engine are analyzed accordingly.

Key words: performance characteristics of two-stroke and four-stroke gasoline engines and diesel engines

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Section 1 Classification of Engines

Engine is a machine that directly converts some energy in nature into mechanical energy and drags some machinery to work. An engine that converts thermal energy into mechanical energy is called a heat engine (heat engine for short), in which thermal 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. It is characterized in 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 to convert the contained thermal energy into mechanical energy.

Compared with external combustion engines, internal combustion engines have the advantages of high thermal efficiency, small size, light weight, convenient movement and good starting performance, so they are widely used in aircraft, ships, automobiles, tractors, tanks and other vehicles. The internal combustion engine generally requires 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, domestic and foreign countries are committed to the research and development of new energy engines such as exhaust gas purification.

According to the different forms of main components that convert thermal energy into mechanical energy, automobile 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 rotating piston according to the different piston motion modes. Reciprocating piston internal combustion engine is the most widely used internal combustion engine in automobile, and it is also the main research object of this paper. Automobile engines (piston internal combustion engines for automobiles) can be classified according to different characteristics:

(1) can be divided into compression ignition engine and ignition engine according to the ignition mode. Compression ignition engine is an internal combustion engine that compresses the air or combustible mixture in the cylinder to produce high temperature and ignite the fuel; Ignition engine is an internal combustion engine that compresses combustible mixture in a cylinder and ignites it with an igniter.

(2) According to the types of fuel used, it can be divided into gasoline engines, diesel engines, gas engines, liquefied petroleum gas engines and multi-fuel engines.

(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 engine refers to an engine in which air or combustible mixture is not compressed by the compressor before entering the cylinder, and a two-stroke engine with only a scavenging pump and no supercharger also belongs to this category; A supercharged engine is an engine in which air or a combustible mixture has been compressed in a compressor to increase the intake density before entering a cylinder.

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(5) According to the number of strokes, it can be divided into two-stroke and four-stroke engines. In an engine, every time thermal 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 fresh charge is air), making it ignite, burn and 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 twice) to complete a working cycle, it is called a four-stroke engine; A two-stroke engine is an engine in which the piston reciprocates twice (or the crankshaft rotates once) to complete a working cycle.

(6) According to the number and arrangement of cylinders, engines with only one cylinder are called single-cylinder engines, and engines with more than two cylinders are called multi-cylinder engines; 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 a row) and opposite (cylinders are arranged in two rows, and the center line between the two rows of cylinders is 180). ) and V-shaped engine (cylinders are arranged in an arc shape, and the included angle between two rows of cylinders is V-shaped).

Section 2 General Structure of Engine

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 different specific structures. We can analyze the overall structure of the engine through some typical structural examples of the automobile engine.

Taking the CA488Q gasoline engine for CA 10 14 series light trucks as an example, this paper introduces the overall structure of the four-stroke chopper (Figure 1- 1).

(1) cylinder block the cylinder 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. As the assembly matrix of engine mechanism and system, engine block has many components, including crank-connecting rod mechanism, valve train, supply system, cooling system and lubrication system. The cylinder head and the gas inner wall constitute a part of the combustion chamber, and they are parts that bear high temperature and high pressure. In structural analysis, the engine block is usually included in the crank-connecting rod mechanism.

(2) Crank-connecting rod mechanism Crank-connecting rod mechanism includes piston 13, connecting rod 10, crankshaft 5 with flywheel 28, etc. It is a mechanism that converts the linear reciprocating motion of the piston into the rotary motion of the crankshaft and outputs power.

(3) Valve mechanism The valve mechanism includes intake valve 19, exhaust valve 15, rocker arm 45, valve lash adjuster 46, camshaft 25 and camshaft timing pulley 20 (driven by crankshaft timing pulley 6). Its function is to fill the combustible mixture into the cylinder in time and exhaust the exhaust gas in the cylinder in time.

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Figure 2- 1 Jiefang CA488Q gasoline engine structure

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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, an exhaust muffler, etc. Its function is to mix gasoline and air into a combustible mixture with appropriate composition and supply it to the cylinder for combustion, so as to discharge the waste gas produced by combustion from the engine.

(5) Ignition system The function of the ignition system is to ensure that the compressed mixture in the cylinder is ignited in time according to regulations. These include batteries and generators that provide 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, and the water jacket is a cavity 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 oil pump 50, oil filter 5 1, pressure limiting valve, lubricating oil channel, oil filter, etc. Its function is to supply lubricating oil to relatively moving parts, so as to reduce the friction resistance between them, reduce the wear of machine parts, and locally 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 make it enter the self-running state.

Automobile 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 engine is shown in Figure 3- 1. A piston 10 is installed in the cylinder, and the piston is connected with the crankshaft 12 through a piston pin and a connecting rod 1 1. The piston moves back and forth in the cylinder and drives the crankshaft to rotate through the connecting rod. In order to suck in fresh air 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 where 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 piston top surface is closest to the crankshaft centerline 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 crankshaft 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) Intake-stroke gasoline engine first mixes air and fuel in the carburetor outside the cylinder, on the throttle body or in the intake port to form a combustible mixture, and then it is sucked into the cylinder.

In the intake process, 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 lower than 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 is about 0.075~0.09Mpa at the end of intake.

(2) Compression Stroke In order to make the combustible mixture sucked into the cylinder burn rapidly, thus generating greater pressure and engine power, it is necessary to compress the combustible mixture before combustion to reduce its volume, increase its density and increase its temperature, so a compression process is needed. In this process, the intake valve and exhaust valve are closed, and the crankshaft pushes the piston to move from bottom dead center to 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 gas mixture rises to 0.6 ~ 1.2 MPa, and the temperature can reach 600 ~ 700 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 ~ 1 1). For example, the compression ratio of EA827 1.6L engine of FAW-Volkswagen Jetta is 8.5, while the compression ratio of EA 1 13 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 fire will appear. Deflagration is an abnormal combustion caused by the high gas pressure and temperature and the 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 will make a sharp knocking sound. At the same time, it will also cause a series of adverse consequences such as engine overheating, power decline and oil consumption increase. Severe deflagration may even cause mechanical damage such as valve burn, bearing bush crack, piston top burn and spark plug insulator breakdown. Surface ignition is another abnormal combustion phenomenon caused by hot surfaces in the combustion chamber (such as exhaust valve head, spark plug electrode and carbon deposit) igniting the mixed gas. When surface fire occurs, accompanied by strong knocking sound (dull), it 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 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 valve and exhaust valve are still closed. When the piston approaches the top dead center, the spark 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 rise rapidly. The highest achievable pressure p is about 3 ~ 5 MPa, and the corresponding temperature is 2200 ~ 2800 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 to output 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 combustible mixture is burned in the exhaust stroke must be discharged from the cylinder for the next working cycle.

When the expansion is near the end, the exhaust valve opens and the exhaust gas is discharged freely under the action of exhaust gas pressure. When the piston reaches the bottom dead center and moves to the top dead center, it will continue to force 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.

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Part of the residual waste gas is called residual waste gas.

To sum up, a four-stroke gasoline engine completes a working cycle through four strokes: intake, compression, combustion work and exhaust. In this problem, the piston reciprocates four strokes between top dead center and bottom dead center, and the crankshaft rotates two times.

Working principle of two-stroke and four-stroke diesel engines

The structure of modern diesel engine is shown in Figure 3-3.

Each working cycle of a four-stroke diesel engine (compression ignition engine) also goes through four strokes: intake, compression, work and exhaust. However, because the fuel of diesel engine is diesel oil, its viscosity is higher than that of gasoline, but its auto-ignition temperature is lower than that of gasoline, so the formation and ignition mode of combustible mixture are different from that of gasoline engine.

Diesel engines inhale pure air in the intake stroke. When the pressure storage stroke comes to an end, the fuel injection pump of diesel engine raises the oil pressure to above 10MPa, which is injected into the cylinder by the fuel injector and mixed with compressed high-temperature air in a short time to form a combustible mixture. Therefore, the combustible mixture of this engine is formed inside the cylinder.

Due to the high compression ratio of diesel engine (generally 16 ~ 22), the air pressure in the cylinder can reach 3.5 ~ 4.5 MPa and the temperature can reach 750 ~ 1000 K at the end of compression, which greatly exceeds the auto-ignition temperature of diesel engine. Therefore, after diesel oil is injected into the cylinder, it will be mixed with air in a short time and immediately ignited and burned. The air pressure in the cylinder rises sharply to 6 ~ 9 MPa, and the temperature also rises to 2000 ~ 2500 K. Driven by high-pressure gas, the piston moves downward, driving the handsome shaft to rotate and do work. Exhaust gas is also discharged into the atmosphere through the exhaust pipe.

Compared with gasoline engines, diesel engines have their own characteristics. The speed of gasoline engines is very high (at present, gasoline engines used in automobiles are the highest).

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The rotating speed is 5000 ~ 6000 rpm, and the rotating speed of gasoline engine for truck is about 4000 rpm). It has the characteristics of small mass, low working noise, easy start, low manufacturing and maintenance costs, and is widely used in cars, light trucks and off-road vehicles. Its disadvantages are high fuel consumption and poor fuel economy. Because of the high compression ratio, the average fuel consumption rate of diesel engine is about 20% ~ 30% lower than that of gasoline engine, and the price of diesel oil is lower, so the fuel economy is good. Generally, most trucks with a loading mass of more than 5t use diesel engines; Its disadvantages are lower rotating speed than gasoline engine (generally, the highest rotating speed is about 2500 ~ 3000 r/min), large mass, and high manufacturing and maintenance costs (because of the high machining accuracy requirements of fuel injection pump and injector). But at present, these shortcomings of diesel engine are being overcome gradually, and its application scope is expanding to medium and light trucks. Some foreign cars also use diesel engines, and the maximum speed can reach 5000 r/min.

It can be seen that of the four piston strokes in a four-stroke engine, only one stroke is power, and the other three strokes are auxiliary strokes. Therefore, in a single-cylinder engine, only half of the crankshaft rotates twice, and the rest is maintained by flywheel inertia. Obviously, in the power stroke, the rotation speed of the crankshaft is higher than the other three strokes, so the rotation speed of the crankshaft is uneven, so the engine is unstable. In order to solve this problem, it is necessary to make the flywheel have a large moment of inertia, which will increase the mass and size of the whole engine. Obviously, the working vibration of a single-cylinder engine is very large. Using multi-cylinder engine can make up for the above shortcomings. So now the car basically does not need a single-cylinder engine. Four-cylinder, six-cylinder and eight-cylinder engines are the most widely used.

In each cylinder of a multi-cylinder four-stroke engine, all the working processes are the same and are carried out in the above order, but the power strokes of all cylinders do not occur at the same time. For example, in a four-cylinder engine, one cylinder does work for every revolution of the crankshaft; In an 8-cylinder engine, the crankshaft has a power stroke every 1/4 revolution. The more cylinders, the more stable the engine works. However, the increase of engine cylinder number will generally make its structure complex and its volume and mass increase.

The working principle of the fourth quarter two-stroke engine

Working principle of one-stroke and two-stroke gasoline engines

The working cycle of a two-stroke engine is completed within two piston strokes, that is, the crankshaft rotates once. There are three holes in the engine cylinder, which can be closed by the piston at some time. The air inlet is communicated with the carburetor, the combustible mixture flows into the crankcase through the air inlet, then enters the cylinder through the scavenging hole, and the exhaust gas can be discharged through the exhaust hole communicated with the exhaust pipe.

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The piston moves upward. When the piston closes all three holes, the last cycle begins to compress, that is, it has been sucked into the cylinder.

Combustible mixture inside, and at the same time form a vacuum degree in the crankcase below the piston (the crankcase of this engine must have sufficient sealing). When the piston continues to rise, the air inlet opens and the combustible mixture flows into the crankcase from the carburetor under the action of atmospheric pressure. When the piston approaches the top dead center, the spark plug emits an electric spark to ignite the compressed mixture. The expansion of high temperature and high pressure gas forces the piston to move downward. The air inlet is gradually closed, and the mixture flowing into the crankcase is precompressed due to the downward movement of the piston. When the piston approaches the bottom dead center, the exhaust hole is opened, and the exhaust gas flows into the atmosphere through the exhaust hole, exhaust pipe and muffler. Pre-compressed fresh mixed gas flows from crankcase to cylinder through scavenging holes, and exhaust gas is swept away. The process that the exhaust gas is swept away and replaced by the fresh air mixture in the cylinder is called the air exchange process of the cylinder.

As can be seen from the above, in a two-stroke engine, the two strokes included in the working cycle are:

(1) In the first stroke, the piston moves upward from the bottom dead center, the previously charged mixture in the cylinder above the piston is compressed, and the new combustible mixture is sucked into the crankcase below the piston from the carburetor.

(2) In the second stroke, the piston moves downward from the top dead center, the work and air exchange processes are carried out above the piston, and the precompression of combustible gas mixture is carried out below the piston.

In order to prevent a large amount of fresh mixed gas from mixing with the exhaust gas and being discharged from the cylinder with the exhaust gas, the top of the piston is made into a special shape, so that the airflow of fresh mixed gas is led upward. In this way, fresh mixed gas can also be used to sweep away the exhaust gas and make the exhaust more thorough. However, in a two-stroke engine, it is difficult to completely avoid the loss of combustible mixture.

Figure 4- 1 is the indicator diagram of a two-stroke engine. Its working cycle is as follows:

The piston moves from bottom dead center to top dead center. When the vent (point A) is closed, the compression process begins. Ignition combustion starts before TDC, and the pressure in the cylinder rises rapidly, and the combustion process is biting. Then the piston expands downward to do work, until 6 o'clock, the exhaust hole opens and begins to exhaust. At this time, the pressure in the cylinder is relatively high, generally 0.3 ~ 0.6 MPa.

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So the exhaust gas is discharged from the cylinder at the speed of sound, and the pressure drops rapidly. When the piston continues to move down, the air exchange hole opens and the fresh combustible mixture in the crankcase enters the cylinder. The exhaust in this time interval is called free exhaust. Exhaust continues until the piston descends to the bottom dead center, and then the exhaust hole is closed upward. The bda curve of indicator diagram is the ventilation process of two-stroke engine, accounting for about 130 degrees ~ 150 degrees crankshaft angle. Then the piston continues upward, and the compression process repeats a new cycle.

Compared with the four-stroke carburetor engine, the two-stroke carburetor engine has the following main advantages:

1) The crankshaft has a power stroke for each revolution. Therefore, when the working volume and rotating speed of a two-stroke engine are the same as those of a four-stroke engine, its power should theoretically be equal to twice that of a four-stroke engine.

2) Because of the high frequency of power work process, the operation of two-stroke engine is relatively uniform and stable.

3) Because there is no special ventilation mechanism, the structure is relatively simple and the mass is relatively small.

4) Easy to use. Because there are few affiliated institutions, it is easy to wear and tear, and there are fewer moving parts that often need to be trimmed.

Due to structural reasons, the biggest disadvantage of two-stroke engine is that it is not easy to clean up the exhaust gas in the cylinder, and the effective working stroke is reduced during ventilation. Therefore, under the same working volume and crankshaft speed, the power of a two-stroke engine is not equal to twice that of a four-stroke engine, but only equal to 1.5 ~ 1.6 times; Moreover, a part of the fresh combustible mixture is discharged with the exhaust gas during ventilation, so the two-stroke engine is not as economical as the four-stroke engine.

Due to the above shortcomings, two-stroke carburetor engines are rarely used in automobiles. However, this kind of engine is widely used in motorcycles because of its low manufacturing cost, simple structure and light weight. Two-stroke engine can improve the disadvantage of poor fuel economy by reducing scavenging loss, so the electronically controlled injection two-stroke engine is developed on the automobile.

Working principle of two-stroke and two-stroke diesel engines

The working process of a two-stroke diesel engine is similar to that of a two-stroke carburetor engine. The difference is that pure air enters the cylinder of diesel engine instead of combustible mixture.

After the air is pressurized by the scavenging pump, it enters the cylinder through the air chamber installed outside the cylinder and many small holes on the cylinder wall (or cylinder liner), and the exhaust gas is discharged through the exhaust valve on the cylinder head.

In the first stroke, the piston moves from bottom dead center to top dead center. Shortly before the start of the trip, the air inlet and exhaust port

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The valve has been opened, and the air flowing from the self-cleaning air pump (the pressure is about 0. 12 ~ 0. 14 MPa) is used to ventilate the cylinder. When the piston continues to move upward, the air inlet is covered, the exhaust valve is closed and the air is compressed. When the piston approaches the top dead center, the pressure in the cylinder rises to 3MPa, the temperature rises to about 850 ~ 1000 K, and the fuel is injected into the cylinder at a high pressure (about 17 ~ 20 MPa), so that the fuel ignites and spontaneously ignites, thus increasing the pressure in the cylinder.

In the second stroke, the piston moves from top dead center to bottom dead center to do work under the expansion of combustion gas. During the 2/3 stroke, the exhaust valve is opened to discharge the exhaust gas. After that, the pressure in the cylinder is reduced and the air inlet is opened for ventilation. Ventilation continues until the piston moves up 1/3 strokes until the air inlet is completely covered.

This kind of engine is called valve and window DC scavenging diesel engine. Compared with the four-stroke diesel engine, the advantages and disadvantages of the two-stroke diesel engine are basically the same as those pointed out when discussing the two-stroke gasoline engine, but because the two-stroke diesel engine uses pure air to sweep the exhaust gas, there is no fuel loss, so it is more economical.

Section 5 Main performance indexes and characteristics of engines

The main performance indicators of the engine include dynamic performance indicators (effective torque, effective power, speed, etc.). ), economic performance index (fuel consumption rate) and operation performance index (exhaust quality, noise and starting performance, etc. ).

I. Dynamic performance indicators

(1) effective torque

The average torque output by the engine through the flywheel is called effective torque. The effective torque is in balance with the resistance torque exerted on the engine crankshaft by the outside world.

(2) Effective power

The power output by the engine through the flywheel is called effective power. It is equal to the product of the effective torque and angular velocity of the crankshaft.

The rotational speed of the engine crankshaft is related to the number of times of work done per unit time or the effective power of the engine, that is, the effective power of the engine varies with the rotational speed of the crankshaft. Therefore, when explaining the effective power of the engine, it is necessary to indicate its corresponding speed at the same time. The power specified on the engine product label and its corresponding rotational speed are called calibrated power and calibrated rotational speed respectively. The working condition of the engine at rated power and rated speed is called rated working condition. Rated power is the maximum power that the engine can emit, and it is the maximum use limit of effective power according to the purpose of the engine. The rated power value of the same engine is different for different purposes. According to the provisions of the reliability test method of automobile engine, automobile

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Under the calibration conditions, the engine should be able to run continuously for 300 ~ 1000 hours.

Second, economic operation indicators

The fuel mass (in g) consumed by the engine per 1 kw effective power within 1h is called fuel consumption rate.

The performance of the engine changes with many factors, and its changing law is called engine characteristics.

Three. Operational performance indicators

Engine performance indicators mainly refer to exhaust quality, noise, starting performance, etc. Because these attributes are not only related to the interests of users, but also to human health, it is necessary to specify a unified standard and strictly control it.

(1) exhaust quality

Engine exhaust contains substances harmful to human body, and its pollution to the atmosphere has become a public hazard. To this end, many countries have taken many countermeasures and formulated corresponding control laws and regulations. The harmful emissions of engines mainly include nitrogen oxides, hydrocarbons (HC), carbon monoxide (CO) and exhaust particles.

(2) Noise

Noise can stimulate nerves, make people feel irritable, slow to respond, and even cause deafness, induce hypertension and nervous system diseases, so it must also be restricted by laws and regulations. Cars are one of the main noise sources in cities, and engines are also the main noise sources of cars, which must be controlled. In China's standard "Limits of External Noise during Acceleration" (GBl495-2002), noise limits are formulated in detail for different types of vehicles and vehicles with different total mass and engine rated power in the same category.

(3) Starting performance

An engine with good starting performance can start reliably at a certain temperature, with rapid start, low power consumption and less wear when starting. The starting performance of the engine is not only related to the engine structure, but also related to the working process of the engine, which directly affects the maneuverability of the car, the safety of the operator and the labor intensity. According to Chinese standards, the gasoline engine should start at-10℃ and the diesel engine should start below -5℃, and the engine should be able to run automatically within 15s without special low-temperature starting measures.

Fourthly, the speed characteristics of the engine.

Curve of engine performance parameters (effective torque, power, fuel consumption rate, etc.) when the position of fuel supply regulating mechanism is fixed. ) with the change of speed is called speed characteristic curve.

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If another set of characteristic curves can be obtained by changing the position of the fuel supply adjusting mechanism, when the position of the fuel supply adjusting mechanism reaches the maximum, the total power characteristic is obtained, which is also called the engine external characteristic; The characteristics obtained at other positions of the fuel supply regulating mechanism are called partial speed characteristics.

The maximum power, maximum effective torque and corresponding speed of the engine marked under the external characteristic curve are important indicators to express the engine performance. It is necessary to analyze whether the external characteristic curve of the engine meets the requirements according to the use of the vehicle, such as the resistance value and the maximum speed required by the road conditions.

Five, the engine working condition

The running state or working state of an engine (engine working condition for short) is often characterized by power and speed, and sometimes by load and speed.

Engine load refers to the power or effective torque consumed by the engine to drive the driven machinery; It can also be expressed as the load of the engine at a certain speed, that is, the ratio of the power emitted by the engine at that time to the maximum power that may be emitted at the same speed, expressed as a percentage.

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thank you

The design of this paper lasted more than three months. I would like to express my sincere thanks to my tutor, Mr. X. From the design and editing of the subject to the writing and revision of the paper, Mr. Qian has given serious guidance and strict requirements. Teacher Qian's profound knowledge, rigorous academic spirit and approachable attitude make me have a good feeling while learning knowledge.

During the research and design of the whole project, we also got the support and help from other students in the same group, and we overcame one problem after another together. Thank you here.

During the four years' study in college, my knowledge and ability have been improved. To this end, I want to thank my family, as well as all the teachers and elders who have taught me, who encouraged me to move forward. In addition, I want to thank my friends and classmates, who make me relaxed and happy every day.

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refer to

1, Chen Jiarui "Automobile Structure" Machinery Industry Press

2. Chen Jiarui "Under the Automobile Structure" Machinery Industry Press

3. Fu Aimin Automotive Application Basic Electronics Industry Press

4. Fu Aimin wrote "Automobile Engine Structure and Maintenance" Electronic Industry Press.

5. Wu Anda Qiao Guorong Automobile Maintenance Technology Higher Education Press

6. Ling Kai Automobile Data Writing Group "Automobile Principles" Beijing University of Posts and Telecommunications Press

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