The gasoline engine is based on gasolineFuel, willinternal energyConvert tokinetic energyEngine.becausegasolineThe viscosity is small and the evaporation is fast. You can use the gasoline injection system to inject gasoline into the cylinder. After compression to a certain temperature and pressurespark plugIgnite to expand the gas and do work.The gasoline engine is characterized by high speed, simple structure, light weight, low cost, stable operation and convenient use and maintenance.Gasoline engines are widely used in cars, especially small cars.
Chinese name
gasoline engine
Foreign name
Gasoline Engine
Fuel
gasoline
Advantages
High speed, simple structure and light weight
Properties
Auto parts
Principle
Burn the fuel in the cylinder to generate kinetic energy
It is the assembly base of all engine parts.It includesThe cylinder cover、Cylinder blockLower crankcase（Oil pan）。The cylinder head and the inner wall of the cylinder block together form a part of the combustion chamber.Many parts of the body are also part of other systems.
Crank connecting rod mechanism
It is the mechanism by which the engine generates and transmits power. It converts the linear reciprocating motion of the piston into the rotary motion of the crankshaft to output power.It includes piston, piston pin, connecting rod, crankshaft with flywheel, cylinder block, etc.
Valve train
Includes inlet valve, exhaust valve, valve tappet andCamshaftAnd camshaftTiming gear(driven by the crankshaft timing gear), etc.Its function is to make the combustible mixture fill the cylinder in time and exhaust the exhaust gas from the cylinder in time.
Fuel supply system
The fuel supply system of gasoline engine includes gasoline tankGasoline pump、Gasoline filter、Air filter、carburetor, intake pipe, exhaust pipe, exhaust silencer, etc.Its function is to mix gasoline and air into a suitable combustible mixture for the cylinder for combustion, and to exhaust the exhaust gas generated by combustion from the engine.
Cooling system
It mainly includes water pump, radiator, fan, water distribution pipe, cylinder block and water jacket in cylinder head.Its function is to distribute the heat of high heat parts to the atmosphere to ensure the normal operation of the engine.
lubrication system
It includes oil pump, pressure limiting valve, lubricating oil passage, filter collector, oil filter, oil radiator, etc.Its function is to supply lubricating oil to friction parts to reduce the friction resistance between them, reduce the wear of parts, and partially cool friction parts and clean friction surfaces.
Starting system
Including the starting mechanism of the engine and its accessories.
characteristic
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becausegasolineWith low viscosity and fast evaporation, it can form a uniform mixture with air outside the cylinder, and then inhale the mixture into the cylinder, or use the gasoline injection system to inject gasoline into the cylinder to expand the gas and do work.The disadvantage of gasoline engine is that its thermal efficiency is lower than that of diesel engine, its fuel consumption is higher, its ignition system is more complex than that of diesel engine, and its reliability and maintenance convenience are also lower than that of diesel engine.
application
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Under the same power condition, the size and mass of gasoline engine are smaller than that of diesel engine;With good torque characteristics, good starting and acceleration performance, low operating noise and low manufacturing cost, gasoline engines are widely used in aircraft, automobiles, speedboats, racing cars, small agricultural machinery, garden machinery and even aircraft models.
working principle
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The engine willchemical energyThe conversion process of a machine that is converted into mechanical energy is actually a work cycle process. In short, it generates kinetic energy by burning the fuel in the cylinder to drive the piston in the engine cylinder to move back and forth, thereby driving the piston connected to thepistonThe connecting rod on the crankshaft and the crank connected with the connecting rod move in a reciprocating circle around the center of the crankshaft to output power.
The working process of the four stroke gasoline engine is a complex process, which consists of intake, compression, combustion expansion and exhausttrip（stroke）Composition.
Intake stroke
At this time, the piston is driven by the crankshaft to move from TDC to TDC. At the same time, the inlet valve is opened and the exhaust valve is closed.When the piston moves from top dead center to bottom dead center, the volume above the piston increases, and the gas pressure in the cylinder decreases, forming a certain vacuum degree.As the intake valve is opened, the cylinder is connected to the intake pipe, and the mixture is sucked into the cylinder.When the piston moves to the bottom dead center, the cylinder is full of fresh mixture and exhaust gas not discharged in the previous working cycle.
Compression stroke
The piston moves from BDC to TDC, and the inlet and exhaust valves are closed.The crankshaft rotates under the inertial action of the flywheel, and the piston moves upward through the connecting rod. The gas volume in the cylinder gradually decreases, and the gas is compressed. The pressure and temperature of the mixed gas in the cylinder increase with time.
Work stroke
At this time, the inlet and exhaust valves are closed at the same time,spark plugIgnition occurs, and the mixture burns violently. The temperature and pressure in the cylinder rise sharply. High temperature and high pressure gases push the piston downward and drive the crankshaft to rotate through the connecting rod.In the four engine working strokes, only this stroke can realize the conversion of heat energy into mechanical energy. Therefore, this stroke is also called the power stroke.
Exhaust stroke
At this time, the exhaust valve opens, the piston moves from bottom dead center to top dead center, and the exhaust gas is discharged from the cylinder as the piston moves upward.Because the exhaust system has resistance and the combustion chamber also occupies a certain volume, it is impossible to exhaust the waste gas completely at the end of the exhaust. This part of the waste gas is called residual waste gas.The residual exhaust gas not only affects inflation, but also has adverse effects on combustion.
At the end of the exhaust stroke, the piston returns to TDC.This completes a work cycle.Then, driven by the inertia of the flywheel, the crankshaft continues to rotate and starts the next cycle.In this way, the engine will keep running.[1]
Common faults
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knock
The gasoline engine will produce knock. To analyze the knock phenomenon, we should understand the causes and solve the problem according to the crux.
The combustible mixture of a gasoline engine is initially ignited by high pressure.Then, the burning flame takes the spark plug as the center, spreads outward, and ignites the mixture in the combustion chamber. This combustion process is normal combustion.If the remaining mixture ignites itself without being ignited before the flame arrives, this combustion is called detonation.
Detonation is not allowed to occur during the normal operation of the engine. It will lead to increased wear of various parts of the engine cylinder block, shortened service life, or even rapid destruction. It will also reduce engine power and increase fuel consumption.
Knock phenomenon:
1. Detonation will suddenly produce shock waves in the cylinder and impact in all directions, causing strong vibration of the piston, cylinder wall, connecting rod, crankshaft, etc. of the engine and irregular metal knocking sound;
2. The temperature of cooling system is too high;
3. Incomplete fuel combustion and black smoke in exhaust gas;
4. Engine power decreases and fuel consumption increases.
resolvent:
1. Reduce ignition advance angle;
2. Use gasoline of the specified brand (octane number);
3. Remove the carbon deposit in the combustion chamber;
4. If a knock occurs when the car is going uphill, shift to the low gear in time;
5. When starting the car, do not shift into the direct gear too early.
6. When the engine is overloaded and has knock, closing the small valve can also play a role in reducing knock.[2]
Cylinder
Cylinder scuffing refers to the phenomenon of up and down scratches in the area where the inner surface of the cylinder liner contacts the reciprocating motion of the piston. Generally, cylinder scuffing often occurs in the running in period after engine overhaul;Some also occur in normal operation.During cylinder drawing, generally there are slight striation marks on the inner surface of the cylinder liner, and less serious lamellar marks.The strained parts are mostly on the surface of both sides of the cylinder liner perpendicular to the piston pin axis.The damaged parts of cylinder drawing are mostly cylinder liner (internal surface), piston (external surface) and piston ring (external contact surface).
The basic reason for cylinder scuffing damage is the local dry friction between the cylinder liner and the piston friction ring.Therefore, the micro convex bodies on the metal surface contact each other.Under the action of high load, the micro bulge deforms. During the mutual movement, a large amount of friction heat is generated, which makes the micro bulge melt and fuse, and then pull apart, forming scratch marks and debris.Metal wear debris is embedded on the piston surface (no lubricating oil washes them away), which scratches the cylinder wall.
There are many factors affecting cylinder scuffing, and the situation is complicated.It is mainly related to the working condition (temperature and load) of the engine, the matching between the piston and cylinder sleeve and the matching materials.However, the running in condition of the engine running in period is the key to affect the cylinder scuffing.There are three basic factors causing cylinder scuffing.
1. The temperature between the piston and cylinder sleeve of the engine is too high
1) The heat load of the engine is too large, which makes the temperature of the whole engine too high. The best heat state of the engine is to keep the cooling water temperature between 75 ℃ and 85 ℃. If the heat load of the engine is too large, or its cooling effect is poor, the engine temperature will be too high, and the piston will expand and deform too much;The clearance between the cylinder liner and the piston is too small, which makes it difficult to form a good lubricating oil film. Even because the lubricating oil is carbonized or burned off at high temperature, the piston ring and the cylinder wall are bonded, resulting in sudden explosion and early combustion, resulting in a dry friction state and increasing engine wear.
2) The accuracy, smoothness and shape (taper and ovality) of the inner surface of the cylinder liner exceed the specified standards.The sealing effect of the piston ring is reduced, and the combustion gas in the cylinder flows into the piston skirt, making the temperature of the skirt too high and the lubrication worse, resulting in local dry friction.
3) The installation position of the piston in the cylinder liner is offset, resulting in eccentric wear. Due to the piston deformation, the piston pin hole is offset, the cylinder honing is skewed, the connecting rod is bent or twisted, the crankshaft is changed, and the crank pin is not parallel to the main journal, etc., the piston will lean against one side in the cylinder.At this time, the pressure of the piston ring on the cylinder wall is relatively concentrated on the local surface, so that the oil film between the cylinder liner and the piston ring becomes thin under great pressure, or even breaks. As a result, lubrication is lost, dry friction is formed, and the temperature increases dramatically.
4) Engine deflagration. When the engine is working, the fuel octane number is too low, the ignition time is too early, the compression ratio is too high, the spark plug is overheated, and carbon deposits in the combustion chamber are serious, which will cause deflagration.As a result, the local temperature of the cylinder wall increases rapidly, the lubricating oil film is damaged or coke is formed into a glue, which sticks the piston ring in the ring groove, causing air leakage.In addition, the combustion gas caused by deflagration strikes the cylinder wall, which makes the cylinder liner prone to dry friction and scratches.
5) The inner surface of the cylinder liner is poorly lubricated.Due to insufficient lubricating oil, low oil pressure, poor oil quality and other factors, the heat generated by metal friction surface can not be taken away during lubrication, which will cause high-temperature deformation of metal.
6) Poor cooling effect.Due to water shortage, internal blockage of radiator, excessive scale on the outer wall of cylinder liner, improper fan installation, loose fan belt, small fan flow, low pump displacement and other factors, the engine will not work well in cold state, resulting in overheating of the engine, excessive water temperature and lubricating oil temperature.In particular, overheating occurs during the running in period, which is prone to cylinder scuffing.
2. Improper material matching of piston ring, piston and cylinder liner
In China, there are many units producing auto parts, the quality of parts is unstable, the piston expansion coefficient of each manufacturer is different, and the surface hardness of cylinder liner and piston ring is also different, which may cause cylinder scuffing. For example, when replacing piston rings, sufficient end clearance should be left according to the standard;Chrome plated cylinder liners should not be equipped with chrome plated piston rings to avoid hard cylinder drawing.
3. Assembly and process problems
1) The piston pin assembly is too tight, which is easy to cause cylinder pulling at both ends of the axial direction;
2) The piston pin retainer ring comes out, which can cause very serious cylinder pulling;
3) The piston ring notch is improperly handled, the ring notch opening is too large, and the edges and corners are prominent when filing;
4) Large end clearance of piston ring;
5) The engine speed rises too fast during cold start, or the load is added too fast.
4. Pay attention to the following points when using
1) During the running in period after the engine is overhauled, the operating procedures, load reduction, deceleration and other provisions during the running in period shall be strictly implemented;
2) Keep the correct ignition time, and avoid setting the ignition time too early, which may cause sudden explosion and overheating of the engine;
3) Ensure enough engine oil of the brand specified by the original manufacturer, check the engine oil pressure frequently, and replace the engine oil according to the running in period;
4) Add enough cooling water and check the cooling water volume and temperature frequently.
In a word, it is a complex and meticulous work to prevent cylinder scuffing. First, we should grasp the key problem of high temperature. Second, we should select the material of mating parts and the fit size gap. Finally, we should ensure the assembly and commissioning process.In this way, the phenomenon of cylinder scuffing can be reduced or avoided.
