Four stroke gasoline engine working principle

inlet

Is the mixture of fuel and air into the engine first;

Intake valve, exhaust valve closed, the piston from TDC down the only point to move above the piston cylinder volume increases, resulting in vacuum, the cylinder pressure is reduced to below the inlet pressure, the vacuum suction effect, through the carburetor or fuel injection device for atomizing gasoline mixed with air to form a combustible mixture, from the inlet the intake valve and suction cylinder. The intake process has been extended to the piston through the lower end of the valve into the valve closed. Then the upward piston begins to compress the gas.

Intake stroke

Due to the rotation of the crankshaft, the piston moves down from top to end, when the exhaust valve closes and the intake valve opens. At the beginning of the intake process, the piston is located at the top end, and there is no exhaust gas in the cylinder, so the pressure inside the cylinder is slightly higher than the atmospheric pressure. With the downward movement of the piston, the cylinder volume increases, the pressure decreases, when the pressure is lower than atmospheric pressure, vacuum suction in the cylinder, the air passes through the air filter and carburetor supply of gasoline mixed into a combustible gas mixture, the intake valve is sucked into the cylinder, until the piston moves down to the next stop point. During the intake process, the air cleaner, carburetor, intake pipe, the intake valve resistance effect, intake, gas cylinder pressure is slightly lower than the atmospheric pressure is about 0.075 ~ 0.09MPa, is also affected by the residual gas and high-temperature mechanical heating, the temperature reached 370 ~ 400K. The intake valve of the actual gasoline engine is opened before the piston reaches the top dead point, and is delayed until the next stop to be closed so as to suck in more combustible mixture.

Job characteristics: intake valve, exhaust valve, piston down.

compress

Is the intake of the engine gas mixture for compression, once compressed, the pressure of the fuel mixture and temperature will rise;

All the intake and exhaust valves are closed, and the mixture of the fuel in the compression cylinder is increased, the temperature of the mixture is increased, and the pressure is increased. Before the piston is near the top dead point, the combustible mixed gas pressure rises to 0.6 ~ 1.2MPa, the temperature can reach 330 degrees Celsius to 430 degrees Celsius.

Compression stroke

The crankshaft continues to rotate, the piston from TDC to BDC movement, then the intake and exhaust valves are closed, the cylinder becomes a closed volume, the combustible mixture is compressed, the pressure and temperature rising, when the piston reaches TDC when the end of the compression stroke. At this time the pressure and temperature of the gas mainly with the compression ratio of the size of the fuel mixture can reach 0.6 ~ 1.2MPa, the temperature can be up to 600 ~ 700K. The larger the compression ratio, the higher the pressure and temperature in the cylinder at the end of compression, the faster the combustion speed, the greater the power of the engine. But the compression ratio is too high, easy to cause deflagration. The so-called deflagration is due to gas pressure and high temperature of the mixture burned in the absence of self ignition, and the flame to the normal combustion rate several times higher than the spread, caused a sharp knock. The engine will overheat, power down, gasoline consumption increased and mechanical damage. A slight deflagration is allowed, but the strong explosion is very harmful to the engine, gasoline engine compression ratio for epsilon = 6 ~ 10.

Working features: intake and exhaust valves are closed, the piston up, cylinder pressure, temperature rise. Automotive maintenance technology network

Work

Is lit has high temperature and pressure of the mixed gas, mixed gas combustion expansion, external output power, this process is known as work;

A spark plug is arranged at the upper end of the cylinder cover to send out electric spark and ignite the compressed combustible mixture when the compression stroke is close to the top dead point. Combustible mixed gas combustion after the release of a large number of heat, gas pressure and temperature in the cylinder rapid rise, the maximum combustion pressure of up to 3 ~ 6MPa, the maximum combustion temperature of up to 2200 degrees Celsius to 2500 degrees celsius. The high temperature and high pressure gas pushes the piston to move down quickly, and the crank connecting rod mechanism is used for the external work. When the work begins, the intake and exhaust valves are closed.

Work schedule

The work schedule includes the combustion process and the expansion process, in which the intake and exhaust valves are closed. When the piston is in compression stroke close to TDC (i.e. ignition angle) position, the spark plug spark ignited combustible mixed gas, combustible gas mixture to give off a lot of heat after combustion in the cylinder gas temperature and pressure increased sharply, the maximum pressure can reach 3 ~ 5MPa, the maximum temperature is 2200 ~ 2800K, high temperature and high pressure the expansion of gases, push the piston from TDC to BDC downward movement of the crankshaft and output mechanical power through the connecting rod, except for maintaining the engine itself continues to run, the rest used for external work.

With the downward movement of the piston, the cylinder volume increases, gas pressure and temperature decrease, when the piston reaches BDC, the power end of the trip, the gas pressure is reduced to 0.3 ~ 0.5MPa, the gas temperature is reduced to 1300 ~ 1600K.

Working features: intake, exhaust valve closed, mixed gas combustion, expansion, piston down.

exhaust

The burned gas must be discharged from the engine to prepare for the second air intake;

Near the end of the power stroke, the exhaust valve, when the cylinder pressure is higher than the atmospheric pressure, the rapid discharge of high temperature exhaust gas cylinder, this stage is free exhaust stage, high temperature exhaust gas through the exhaust valve to the local speed of sound. With the process of exhaust gas into the forced exhaust stage, the piston over the lower dead point to move up and down, forced to discharge the exhaust gas, the piston reaches the top dead point, the exhaust process is over. At the end of the exhaust gas, the gas pressure in the cylinder is slightly higher than the atmospheric pressure, which is about 0.105 ~ 0.115MPa, and the exhaust gas temperature is about 600 degrees C to 900 C. Because of the combustion chamber