by MOU YONG HONG on October 07, 2021

Analysis of the causes of black smoke:

Cummins diesel engine exhaust emits black smoke, which is a phenomenon in which diesel is not fully burned, and carbon is decomposed and discharged with exhaust gas under high-temperature conditions. This phenomenon not only reduces engine power, increases diesel consumption, but also easily forms carbon deposits and shortens the service life of the engine. The reasons are as follows:

1. Insufficient fresh air in the cylinder

Reasons: (1) too much dust in the air filter element;
(2) rust, carbon deposits, or oil on the muffler.
(3) The clearance between the intake and exhaust valves is too large, which reduces the valve opening;
(4) The parts of the distributor are loose, worn, deformed, the relative position of the camshaft gear and the crankshaft timing gear changes, and the valve opening and closing time is incorrect.

2. Reasons for temperature and pressure drop at the end of cylinder compression:

(1) Excessive wear of the cylinder barrel and piston ring, improper installation of the piston ring, or loss of elasticity, causing the cylinder to leak;
(2) If the valve clearance is too small, it is easy to be ejected when the car is hot, or the valve is ablated or carbon deposits cause the cylinder The seal is not tight;
(3) The cylinder head and the body, the joint surface of the injector and the cylinder head are leaking;
(4) The valve is severely sinking, the piston and the piston pin, the piston pin and the connecting rod are small, and the connecting rod is big and the connecting rod shaft The neck gap is too large, which increases the volume of the combustion chamber and decreases the compression ratio.

3. Poor diesel atomization

Reasons: (1) Injector pressure adjustment is too low;
(2) Injector pressure regulating spring is broken or stuck;
(3) Injector needle valve and valve seat are carbonized, and the needle valve is stuck or worn too much;
(4) ) The decompression ring belt of the fuel injection pump outlet valve is worn too much, causing the fuel injector to drip.

4. the fuel supply time and fuel supply are not correct

The reasons are: (1) The fuel supply time is too late;
(2) At the beginning of starting, the gas pressure and temperature are low, and the fuel supply time is too early;
(3) The fuel injection pump plunger and even parts wear out and increase the fuel supply stroke to use;
(4) The stroke of the fuel injection pump adjustment rack or tie rod is too large, resulting in excessive fuel supply.


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