Problem: The crankshaft does not rotate when the diesel engine is started; the exhaust pipe does not smoke when the diesel engine is started; white smoke is emitted from the exhaust pipe when the diesel engine is started.

●  Failure cause analysis:

For diesel to be burned in a diesel engine, fuel, fire (temperature generated by the piston during the compression stroke) and combustion-supporting (air) conditions must be present. If the diesel engine cannot start, it obviously does not meet the above conditions.

1. Since the starter is faulty and cannot rotate, the diesel engine cannot inhale air, inject fuel, and generate compression temperature, resulting in the diesel engine not being able to start.

2. The impact of the fuel supply system. It can be seen from the working principle of the engine that the fuel system should inject fuel into the cylinder in a timely and appropriate amount and ensure the atomization quality so that the fuel burns well; the working quality of the fuel system is mainly reflected in the injection time, fuel injection amount and Atomization quality.

If there is a fault in the fuel system, it will be difficult to ensure the time, quantity and atomization quality of fuel injection into the cylinder, making it difficult to start the engine; a common phenomenon is that the exhaust pipe is smokeless ( Most of them are without fuel), that is, there is no sign of starting.

3. Poor compression in the cylinder. Cylinder compression must be carried out under closed conditions, that is, the piston moves upward from the bottom dead center, the volume above the piston decreases, and the pressure and temperature increase. If the gas-containing parts in the cylinder are poorly sealed.

That is, air leakage will occur during the compression stroke, resulting in poor compression. When the compression is completed, the gas pressure and temperature cannot rise, which lacks fire conditions for fuel combustion, causing the injection If the diesel fuel entering the cylinder cannot ignite and burn on its own, the diesel engine cannot start.

4. The influence of temperature. When a diesel engine is started, the piston in the cylinder compresses the air to generate high temperature, causing the atomized diesel fuel injected into the cylinder to evaporate and be fully mixed and oxidized for combustion, thereby pushing the piston to move to generate power.

If the ambient temperature is low and the machine body is cold, the heat exchange rate between the heat entering the compressed air in the cylinder and the machine body will increase, causing the gas temperature in the cylinder to drop sharply, which will not only cause the fuel The evaporation effect becomes worse, and it is also difficult for the fuel to ignite and burn on its own (lack of fire conditions for fuel combustion), so the engine cannot start; the fuel that fails to burn and atomize is discharged from the body in a milky white color.

5. The gas matching phase is wrong. The moment when the intake and exhaust valves of each cylinder of the engine begin to open and close is usually expressed by the crankshaft angle, which is called the valve timing.

If the valve phase deteriorates with the change of the technical condition of the valve mechanism, such as keyway or key damage and misalignment, excessive valve clearance, wear of cam and timing gear, cam Torsional deformation of the shaft and crankshaft will destroy the original valve phase. In mild cases, it will affect the power of the engine. In severe cases, it will make it difficult for the diesel engine to start.

6. Improper installation. When the timing gear mark is installed out of alignment during maintenance, it not only affects the valve timing, but also affects the fuel supply timing of the fuel injection pump, causing the engine to fail to start.

7. The fuel quality is poor. Water or cooling water in the fuel leaks into the cylinder, preventing the engine from starting. The water entering the cylinder is heated and evaporates into steam, which is discharged from the body as white smoke.

●  Diagnosis and troubleshooting:

1. If the crankshaft does not rotate when the engine is started, it means that the starter is faulty. Diagnose and eliminate starter faults as described in the electrical system.

2. If there is no smoke from the exhaust pipe when starting the engine, it is mostly due to a fault in the fuel system, which should be diagnosed and eliminated according to the faults described in the fuel system.

3. If the exhaust pipe emits white smoke and cannot be started, it means that the engine temperature is too low, the fuel atomization is poor, or the temperature cannot reach the auto-ignition point and cannot be burned, so that the engine cannot be started. Start according to the low temperature start operation method, that is, preheat the engine (including lubricating oil).

4. If the temperature is normal and white smoke still comes out of the exhaust pipe when the engine is started, you should check whether there is water or cooling water in the fuel leaking into the cylinder.

5. If the temperature is normal, the diesel engine is nearing its wear-out period (that is, the parts are severely worn), or the engine seal is poor due to other reasons, the diesel engine cannot start due to poor compression.

Use a cylinder pressure gauge to measure cylinder pressure. If the cylinder pressure is too low, it means that the cylinder has poor compression. The cause of the poor compression should be identified and eliminated.

6. If the diesel engine can start before maintenance but cannot start after maintenance, check whether the timing gear marks are aligned.

• PREV: Agricultural diesel engine tec···
• NEXT: How are diesel silent generato···