What Are The Reasons for Black Smoke Emitted by Diesel Engines?

Black smoke emitted by diesel engines is a malfunction caused by incomplete fuel combustion. This type of malfunction will lead to an increase in fuel consumption and a decrease in power of the diesel engine, resulting in a large amount of carbon deposition in the piston, piston ring valves, and combustion chamber. In severe cases, it may cause air leakage due to jamming of the piston ring and valve, etc; At the same time, it will also accelerate component wear and reduce the service life of diesel engines. Therefore, when a black smoke fault occurs in a diesel engine, it should be promptly resolved. The main reasons for black smoke emitted by diesel engines are:

(1) Poor fuel atomization

Poor fuel atomization results in a longer time for the formation of a mixture after injection into the cylinder, resulting in longer combustion time. The fuel is discharged from the cylinder before it has fully burned, resulting in black smoke from the diesel engine. The main reasons for poor fuel atomization are: ① the pressure adjustment of the fuel injector is too low. ② The pressure regulating spring of the fuel injector is broken or jammed. ③ The nozzle coupling of the fuel injector has accumulated carbon, causing the nozzle to become stuck or excessively worn. ④ The pressure reducing ring of the fuel injection pump outlet valve is excessively worn, causing the fuel injector to drip oil

(2) Low cylinder compression pressure

The temperature and pressure decrease at the end of cylinder compression. Poor compression in the cylinder, resulting in a decrease in compression pressure. This may be due to excessive wear on the piston and cylinder liner, excessive wear on the piston ring, or the opening in the same direction, causing air leakage in the cylinder; It may also be due to poor valve sealing and air leakage. Poor compression in the cylinder, low temperature at the end of compression, and reduced air leakage, resulting in incomplete combustion of diesel and black smoke. The main reasons for poor cylinder compression are: ① excessive wear on the cylinder liner and piston rings, incorrect installation or loss of elasticity of the piston rings, resulting in cylinder leakage. ② The valve clearance is too small, which can easily be pushed open during hot driving, or the valve may be burned or deposited, resulting in poor cylinder sealing There is air leakage at the interface between the cylinder head and the engine body, as well as between the fuel injector and the cylinder head. ④ The valve seriously sinks, causing excessive clearance between the piston and piston pin, piston pin and connecting rod small end, and connecting rod large end and connecting rod journal, resulting in an increase in combustion chamber volume and a decrease in compression ratio

(3) Insufficient fresh air in the cylinder

The air filter or intake pipe is blocked, reducing the amount of air entering the cylinder, incomplete combustion of diesel, and black smoke from the exhaust. If the fuel injector is normal, the compression in the cylinder is good, and the diesel engine emits black smoke after being loaded at high and low speeds. At this time, after removing the air filter, the black smoke immediately disappears, and the air filter needs to be cleaned. Main reasons: ① Excessive dust accumulation in the air filter element. ② Rust, carbon accumulation, or oil stains on the muffler. ③ Excessive clearance between the intake and exhaust valves reduces the valve opening. ④ Loose, worn, deformed parts of the valve train, changes in the relative position between the camshaft gear and the crankshaft timing gear, incorrect valve opening and closing time

(4) Incorrect fuel supply time and quantity

The fuel supply time is too late, and the fuel injected into the cylinder misses the optimal time for mixture formation and combustion. A large amount of unburned fuel is discharged from the cylinder, resulting in black smoke from the diesel engine. If the fuel injection quantity is too large, it will make the mixture too rich, which will also prevent the fuel from fully burning. The main reasons for incorrect fuel supply time and quantity are: ① too late fuel supply time. ② In the early stage of starting, the gas pressure and temperature are low, and the fuel supply time is too early Increase the fuel supply stroke after the plunger coupling of the fuel injection pump is worn. ④ Excessive fuel supply due to excessive stroke of the fuel injection pump fuel adjustment rod

(5) Incorrect valve timing

Excessive valve clearance, valve timing