The flash combustion of gasoline generator set is a kind of abnormal combustion caused by the spontaneous combustion of the terminal combustible mixture in the combustion chamber far from the ignition center due to the high gas pressure and temperature. During flash combustion, the flame spreads outward at a very high rate. Even when the gas has no time to expand, the temperature and pressure rise sharply, forming a pressure wave and advancing at the speed of sound. When this pressure wave strikes the combustion chamber wall, it will make a sharp knock on the cylinder.
At the same time, it will also cause a series of adverse consequences such as engine overheating, power reduction, and fuel consumption increase. Severe flashover may even cause valve burning, bearing bush rupture, spark plug insulator breakdown and other mechanical damage. In addition to flash ignition, engines with high compression ratio may also face another problem: Surface ignition: This is another kind of abnormal combustion (also known as hot ignition or early ignition) caused by ignition of the mixture on the hot surface and hot place (such as exhaust valve head, spark plug electrode and carbon deposit) in the cylinder. When surface ignition occurs, there is also a strong knocking sound (relatively dull). The high pressure generated will increase the engine load and reduce the service life.
Expansion stroke: In this process, the inlet and exhaust valves are still closed. When the piston is close to TDC, the spark plug emits an electric spark to ignite the compressed combustible mixture. After the combustible mixture is burned, a large amount of heat energy is released. At this time, the pressure and temperature of the gas increase rapidly. The maximum pressure it can reach is 3-5 MPa, and the corresponding temperature is as high as 2200-2800K. The high temperature and high pressure gas pushes the piston to move from the top dead center to the bottom dead center. Through the connecting rod, the crank rotates and outputs mechanical energy. In addition to maintaining the continuous operation of the engine itself, the rest is used for external work. During the movement of the piston, the volume in the cylinder increases, and the gas pressure and temperature drop rapidly. At the end of this journey, the pressure drops to 0.3-0.5MPa, and the temperature is 1300-1600K.
Exhaust stroke: When the expansion stroke (work stroke) is close to the end, the exhaust valve opens, and the exhaust gas is discharged freely by the pressure of the exhaust gas. When the piston reaches the bottom dead center and then moves to the top dead center, the exhaust gas is forced into the atmosphere, which is the exhaust stroke. During this stroke, the pressure in the cylinder is slightly higher than the atmospheric pressure, about 0.105-0.15MPa. When the piston reaches the top dead center, the exhaust stroke ends, and the exhaust gas temperature is about 900-1200K.
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