The fuel contains non-combustible particulate impurities. When mixed with unburbible impurity particles in the oil entering the combustion chamber, these impurity particles will discharge the cylinder with the exhaust gas, and a certain chance will have a certain chance in the exhaust valve to be blocked when the exhaust valve is closed. Valves and seat surfaces of the valve seat. The exhaust valve cannot be completely closed. How much is the diameter of the particulate impurities, how large is the opening of the valve.
Although the particulate impurities that can enter the combustion chamber through the spray hole of the injector are small, when the fuel mixed gas exploded, the explosive pressure of the combustion chamber is high, and the tiny air valve opening can also cause high temperature and high pressure combustion gas. Go out. At this time, the temperature of the burning gas is very high, the peak of the moment is close to 2000 ° C, which is much higher than the exhaust gas temperature flowing through the exhaust valve sealing surface in the exhaust stroke. The sealing surface material of the exhaust valve can result in the flushing of the exhaust gas during normal exhaust, but can not afford such high pressure and high temperature combustion gases, the exhaust valve is burned very short time.
In particular, the valve card is mixed in heavy oils and the silica these very hard particles, which causes the exhaust valve to close, and the normal exhaust valve sealing cone is not very high, deposition. The hard combustion product particles can be embedded into the sealing surface under the impact of the closed valve, and a pit is formed under the flushing and ablation of high temperature gas, and the pump is formed to form a leakage to burn the gas valve.