Engine emits blue smoke, white smoke, black smoke

- Jul 10, 2020-

Engine as power systems engineering machinery, mechanical work needed to power it once failure will affect normal production. Therefore, it is very important to diagnose diesel engine failure by observing the color of exhaust gas.

After the diesel fuel is completely burned, the normal color is generally light gray, and the load is slightly dark gray. Abnormal phenomena such as black smoke, white smoke, and blue smoke appear during the operation of the diesel engine. It is a condition to judge whether the diesel engine is malfunctioning.



Black smoke


Diesel is a complex hydrocarbon. Unburned diesel injected into the combustion chamber is decomposed by high temperature to form carbon black. When exhausting, it is discharged together with exhaust gas to form black smoke. Black smoke is a manifestation of incomplete combustion of fuel in the combustion chamber.



The main influencing factors are as follows:

1.Piston ring, cylinder liner and other wear

After the piston ring and cylinder liner are worn, the compression pressure is insufficient, so that at the end of the compression stroke, the normal ratio of the mixed gas mixture changes, so that the fuel is burned under oxygen-free conditions, resulting in carbon deposition.



2.Bad injector work

The fuel injector does not atomize or drip oil, so that the fuel cannot be fully mixed with the air in the cylinder, nor can it be fully burned. The phenomenon of black smoke emission caused by poor work of the fuel injector is more obvious when the diesel engine runs at low speed. Because the intake vortex in the cylinder is weak during low-speed operation, the possibility of oil droplets or oil beams being scattered by the airflow is reduced and the residence time is longer, so it is easier to form carbon black discharge.



3.Combustion chamber shape changes

The manufacturing quality of the shape of the combustion chamber does not meet the technical requirements. If the compression residual gap is too large or too small and the piston is installed in the wrong position, the shape of the combustion chamber will be changed, which will affect the quality of the fuel and air mixture and deteriorate the fuel combustion conditions.



4.Improper adjustment of fuel supply advance angle

① The fuel supply advance angle is too large, and the fuel is injected into the combustion chamber prematurely. Because the pressure and temperature in the cylinder are low at this time, the fuel cannot be ignited and burned. When the piston moves upward, the cylinder reaches a certain pressure and temperature, and the combustible mixture is burned.

② The advance angle of the fuel supply is too small, and the fuel injected into the cylinder is too late. Some of the fuel is separated or discharged before it forms a combustible mixture. The fuel discharged with the exhaust gas is decomposed by high temperature to form black smoke.




Blue smoke    


Lubricating oil enters the cylinder and evaporates into blue oil and gas upon heating. The blue smoke is discharged with the exhaust gas, the main reasons are:

1. The air filter is blocked, the air intake is not smooth, or the oil level in the oil basin is too high (oil bath air filter).

2. Lubricant is mixed in the fuel.

3. Piston ring opposite,

4. The cylinder head gasket near the oil passage leading to the cylinder head is burnt out.

5. Piston ring, piston, cylinder liner wear




White smoke    


When the diesel engine is just started or when it is cold, the exhaust pipe emits white smoke, which is caused by the evaporation of oil and gas due to the low temperature in the cylinder of the diesel engine. It is particularly obvious in winter. If the exhaust pipe still emits white smoke when the engine is warmed up, it is determined that the diesel engine is faulty. The main reasons are as follows:

1. The cylinder liner is cracked or the cylinder head gasket is damaged. Cooling water enters the cylinder and forms water mist or water vapor during exhaust.

2. The atomizer of the fuel injector is bad, and there is oil dripping.

3. The fuel supply advance angle is too small.

4. There is moisture and air in the fuel.

5. The pressure of the fuel injection pump is too low or the wear of the piston and cylinder liner is serious, resulting in insufficient compression force.