Analysis and Fault Diagnosis of Exhaust Gas Color of Diesel Engines in Construction Machinery

Analysis and Fault Diagnosis of Exhaust Gas Color of Diesel Engines in Construction Machinery

As the power system of construction machinery, diesel engines provide the power needed for mechanical operation. Once they malfunction, it will affect normal production. Therefore, it is very important to diagnose diesel engine faults by observing the color of exhaust gas.

After the fuel of a diesel engine is completely burned, its normal color is generally light gray, and it turns dark gray when the load is slightly heavy. During the operation of a diesel engine, abnormal phenomena such as black smoke, white smoke, and blue smoke may occasionally occur. These are the conditions for diagnosing diesel engine faults. The analysis is as follows:

(1) Black smoke

Diesel is a complex hydrocarbon. Unburned diesel injected into the combustion chamber decomposes at high temperatures, forming carbon black. When exhausting, it is discharged along with the exhaust gas, forming black smoke. Black smoke is a sign of incomplete fuel combustion in the combustion chamber. The main influencing factors are as follows:

Wear of piston rings, cylinder liners, etc

When the piston rings and cylinder liners wear out, it leads to insufficient compression pressure. At the end of the compression stroke, the normal proportion of the mixture in the cylinder changes, causing the fuel to burn in an oxygen-free environment and resulting in carbon deposits.

2. The fuel injector is not working properly

If the fuel injector does not atomize or drip fuel, the fuel cannot be fully mixed with the air in the cylinder and cannot be fully burned. The phenomenon of black smoke emission caused by poor operation of the fuel injector is more obvious when the diesel engine is running at low speed. Because the intake vortex in the cylinder is weak during low-speed operation, the possibility of oil droplets or oil bundles being dispersed by the airflow is reduced and they stay for a longer time, making it easier for carbon black to form and be discharged.

3. Change in the shape of the combustion chamber

If the manufacturing quality of the combustion chamber shape does not meet the technical requirements, causing the compression clearance to be too large or too small, or the piston position to be installed incorrectly, the shape of the combustion chamber will change, thereby affecting the quality of fuel and air mixing and deteriorating the fuel combustion conditions.

4. Improper adjustment of the fuel supply advance Angle

(1) If the fuel supply advance Angle is too large, the fuel will be injected into the combustion chamber too early. At this time, the pressure and temperature inside the cylinder are relatively low, and the fuel cannot ignite and burn. When the piston moves upward and the pressure and temperature inside the cylinder reach a certain level, the combustible mixture will ignite.

(2) If the fuel supply advance Angle is too small, the fuel injected into the cylinder is too late. Some of the fuel does not have time to form a combustible mixture before it is separated or discharged. The fuel discharged with the exhaust gas is decomposed by high temperature, resulting in black smoke.

5 The fuel supply is too large

Excessive fuel supply increases the amount of fuel entering the cylinder, resulting in more fuel and less gas, and incomplete fuel combustion. In addition, excessive workload, poor fuel quality and excessively low working temperature can also cause black smoke to be emitted from the exhaust.

(2) Blue smoke

The lubricating oil enters the cylinder and evaporates due to heat, turning into blue oil vapor. Blue smoke is discharged along with the exhaust gas. The main reason for this is:

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

2. Lubricating oil is mixed into the fuel.

3. Piston ring alignment

4. The cylinder gasket near the oil passage from the engine block to the cylinder head was burned out.

5. Wear of piston rings, pistons and cylinder liners

(3) White smoke

When a diesel engine is just started or in a cold state, white smoke comes out of the exhaust pipe because the temperature inside the cylinder is low and the oil vapor evaporates. This is particularly evident in winter. If white smoke still comes out of the exhaust pipe when the engine is heated up, it is judged that there is a fault with the diesel engine. The main reasons are as follows

1. If there are cracks in the cylinder liner or the cylinder gasket is damaged, cooling water will enter the cylinder and form water mist or water vapor during exhaust.

2. The atomization of the fuel injector is poor, and there is a dripping phenomenon.

3. The fuel supply advance Angle is too small.

4. There is moisture and air in the fuel.

5. Insufficient compression force is caused by low pressure of the fuel injection pump or severe wear of the piston, cylinder liner, etc.