Two-stroke and four-stroke comparison between two-stroke and four-stroke engines
Introduction to motorcycle engine
The internal combustion engine is used in the power unit of the motorcycle; People usually call the engines that use diesel as fuel, but the engines that use gasoline as fuel are called diesel.
A gasoline engine. Because the gasoline engine has the advantages of light weight, small volume, noise, small vibration, easy to start, and low cost, so the gasoline engine is widely used in motorcycles.
Two-stroke motorcycle engine working principle
The piston moves from Bottom Dead Center to Top Dead Center, which will complete the process of air intake and compression, and belongs to the first stroke of the piston reciprocating motion. The piston moves from Top Dead Center to Bottom Dead Center.
The utility model completes the work process of combustion expansion (work) and gas discharge, and belongs to the second trip of the piston reciprocating motion. When the piston moves from Bottom Dead Center to Top Dead Center and fully closes
When the vents and vents are closed, the exhaust and ventilation process ends, and the fresh and fuel mixture in the cylinder initially begins to compress. Meanwhile, because the piston moves up, the bottom of the piston
The volume of the crankcase gradually increases, which causes the pressure in the crankcase to decrease to form the degree of vacuum. When the vacuum degree of the crankcase reaches a certain degree, the reed valve automatically opens and atomizes through the carburetor.
The fuel mixture is introduced into the crankcase. As the piston continues to move up and approaches Top Dead Center, an electrical spark is emitted by the spark plug to compress the combustible mixture.
Turn on. At this time, the combustion gas expands rapidly, causing the temperature and pressure of the combustion chamber to rise dramatically, forcing the piston to move downward, that is, through the connecting rod and the crankshaft to do useful work.
When the piston moves from Top Dead Center to Bottom Dead Center, the pressure in the crankcase will increase with the decrease in volume, and the spring valve will gradually close automatically.
The mixture begins to be pre-compressed. When the piston descends to the exhaust port, the exhaust gas is discharged into the atmosphere through the exhaust port, exhaust pipe, and muffler. As the piston continues to drop to the replacement
When the air port is opened, the pre-compressed fresh fuel mixture in the crankcase enters the cylinder through the air exchange port and drives the exhaust gas from the cylinder to further discharge.
sweeping process. This completes one work cycle of the motor.
Four-stroke engine working principle
First Stroke - - - - - - - Air Intake Stroke: When the piston is at a specified crank angle before Top Dead Center, the intake valve opens and fuel mixture is drawn into the cylinder. When the piston moves from Top Dead Center
When the exhaust valve closes at the specified crankshaft rotation angle at Top Dead Center, the volume of the cylinder above the piston increases, causing the cylinder to form a combustible vacuum mixture
Continue inhaling through the intake valve. When the piston moves to a certain crank angle after Bottom Dead Center, the intake valve closes, at this time, the intake work process ends.
Second Stroke - - - - - - - Compression Stroke: Piston moves from Bottom Dead Center to Top Dead Center. When the intake work process ends, the intake valve and exhaust valve are closed.
The fuel mixture in the cylinder begins to compress.
Third Stroke - - - - - - - Combustion Expansion Duty Stroke: During the compression stroke, when the piston moves up to a certain crank angle before Top Dead Center, fire is emitted between the Electrodes of the spark plug
The flowers will be lit with a compressed fuel mixture. The burning fuel mixture causes the temperature and pressure in the cylinder to increase dramatically, while the piston is under the action of high temperature and air pressure.
The movement from Top Dead Center to Bottom Dead Center and the rotation of the crankshaft through the connecting rod do useful work.
Fourth stroke - - - - - - - exhaust stroke: in the combustion expansion stroke, when the piston moves to a certain crankshaft rotation angle before Bottom Dead Center, the exhaust valve opens, the gas exhaust passes through the exhaust valve
It starts to drain. The crankshaft continues to rotate and push the piston up from Bottom Dead Center. Push the exhaust gas out of the cylinder. This exhaust process occurs until the piston moves to top dead center
Specify the angle of rotation of the crankshaft and finish when the exhaust valve is closed
Advantages and disadvantages of the two-stroke motorcycle engine
Each spin bursts once, so the rotation is smooth.
No valves needed, fewer parts, so maintenance is convenient and cheap.
The inertial force generated by the reciprocating motion is small. Low vibration and noise.
Compared with the four-stroke engine, the rotational power is higher at the same time.
Compared to four-stroke, it has twice the explosive force. Therefore, at the same volume, if the mean effective pressure is the same, the Power is 2 times (1.7 actually).
Advantages and disadvantages of the four-stroke engine
Air intake, compression, expansion (explosion) and exhaust process are carried out separately, so the work is reliable, efficient and stable. Wide range of speeds from low to high speed
There is no loss of gas flow and return like the two-stroke engine, and the fuel consumption rate is low.
Smooth running at low speed, lubricated by lubrication system, not easy to overheat.
The air intake process and the compression process have a long time, high volumetric efficiency and high mean effective pressure.
The thermal load is less than the two-stroke engine. Don't worry about deformation or ablation. Large displacement, can be designed into high power motor.
Complex valve mechanism, many parts, difficult to maintain
Because the crankshaft explodes once in 2 revolutions, the rotation balance is unstable.