Analysis of diesel engine exhaust pipe smoke

(I) Continuous exhaust pipe smoke:

Incomplete combustion will cause black smoke. The reason is that the injection quality of the injector has seriously deteriorated, the piston ring and the cylinder wall are seriously worn, the gas leakage has increased, the air filter is dirty, the fuel supply starts too late, the valve transmission mechanism is seriously worn, and the valve opening height is delayed, resulting in reduced intake volume and unclean exhaust.

When checking, first observe whether the black smoke discharged from the exhaust pipe is accompanied by oil and fire discharge. If this phenomenon occurs, the injection quality of the injector is poor. The injectors should be removed one by one and the injection should be checked on the test bench. If the black smoke discharged from the exhaust pipe is accompanied by blue smoke, the oil indicator light is on, the crankcase ventilation device pipe mouth smokes seriously, and the oil consumption increases, the piston ring and the cylinder wall are seriously worn. The cylinder pressure should be used to check the sealing of the cylinder. The compression force of the cylinder should not be less than 80% of the normal pressure, otherwise the piston ring should be replaced or the cylinder should be bored and the cylinder liner should be replaced.

If the above inspection results are good, the air filter cover should be removed, the filter element should be taken out, the engine should be started, and the exhaust pipe should be observed to see if black smoke continues to be emitted. If black smoke is not emitted, it indicates that the air filter is seriously dirty and the filter should be cleaned or the filter element should be replaced. Otherwise, the fuel supply start time should be checked to see if it is too late. If the fuel supply start time is normal, it indicates that the fault is caused by the lowering of the valve opening height.

(II) Intermittent black smoke from the exhaust pipe

Intermittent black smoke is caused by incomplete combustion of individual cylinders. The specific reasons are that the injection quality of the fuel injector of individual cylinders is poor, the piston ring and the cylinder wall are seriously worn, or the valve leaks, resulting in a reduction in the air intake of the cylinder, and the fuel supply time of individual cylinders is too late. At this time, the oil cut-off method can be used to cut off the high-pressure oil circuit from the fuel injection pump to the fuel injector cylinder by cylinder, stop the work of each cylinder one by one, and observe the changes in the exhaust gas to find the cylinder emitting black smoke. Then, replace the cylinder with a standard injector and observe whether black smoke is still emitted. If the black smoke disappears, it indicates that the fault is caused by the poor injection quality of the cylinder injector. Otherwise, it is caused by poor sealing of the cylinder or delayed fuel supply.

1. Check the air supply system

If the diesel engine does not have enough air intake, the amount of air entering the combustion chamber is too small, the diesel is not burned fully, and part of the diesel turns into carbon black particles under high pressure to form black smoke. At this time, you should check: whether the air filter and the intake duct are blocked; the working condition of the supercharger and whether the intake manifold is leaking; the change of the valve timing, whether the valve is correct, whether the intake and exhaust valve seats are leaking; whether the piston, piston ring, and cylinder liner are excessively worn and poorly sealed.

2. Check the diesel supply system. Poor fuel supply in the diesel engine will lead to poor mixing. Even if the intake is sufficient, it cannot be completely burned, thus forming black smoke. At this time, you should check: whether the high-pressure oil pump is improperly adjusted, resulting in excessive fuel supply; whether the oil outlet valve is malfunctioning, causing secondary injection or oil dripping from the injector; whether the injection pressure of the injector is reduced, resulting in poor atomization, oil dripping from the injector, or the injector gasket is over-installed or missing, resulting in incomplete injection; whether the poor combustion is caused by poor diesel quality.