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Diesel Generator Start-up Failure Causes

Nov. 30, 2019

Diesel generator start-up failure or difficult to start

1. Failure phenomenon

a. No explosion sound in the cylinder, white smoke from the exhaust pipe;

b. Black smoke from the exhaust pipe.

Practice has proved that in order to maintain the smooth start of diesel generators, four necessary conditions must be met: a. It must have a certain speed; b. The oil and gas circuits must be unobstructed; C. The cylinders are well compressed; d. The fuel supply timing. From the above prerequisites for starting a diesel generator, it can be inferred that the diesel generator cannot start or is not easy to start.


2. Failure cause

Diesel engine speed is low; a. Starting speed is too low; b. Improper adjustment after pressure reducing device is not put into the correct position; c. Improper adjustment of valve clearance.

The oil and gas paths are not smooth; a. There is no diesel oil in the fuel tank, the oil pipeline is blocked, the fuel filter element is blocked, and oil switch is not open; b. When the diesel engine is started, the ambient temperature is too low; c. There is water or air in the oil path; d. The fuel injection nozzle is poorly sprayed or does not spray fuel; e. The air filter element is blocked or dirty.

Cylinder compression is not good; a. The clearance between the piston and cylinder wall is too large; b. The piston ring is broken or the elastic force is too small; c. The intake and exhaust valves are not closed tightly.

The fuel supply is not correct; a. The injection time is too early (it is easy to kill the injection pump) or too late; b. The valve distribution is not on time.


3. Inspection method

The failure should be carefully observed before inspection. For the diesel generator cannot start or start difficulty of this failure, it is usually judged and checked based on several different faults.

For diesel engines that use electric starting, if the starting speed is very slow, most of these faults are that the starting motor is weak, which does not mean that the diesel engine itself has a fault. It should be checked on the starting circuit to determine whether the battery has sufficient electricity, whether the wires are tightened well and whether the starter motor works well, and whether the air filter element is blocked.

The starting speed is normal, but cannot catch fire. There is no burst sound or intermittent burst sound from the cylinder, and the exhaust pipe emits white smoke. Through this phenomenon, it means that the diesel does not burn in the body and becomes steam exhaust or excessive moisture in the diesel oil.


Diesel Generators


First check whether the ambient temperature at the start of the diesel generator is too low, and then check whether there is air or moisture in the oil circuit.


The oil circuit joint of the diesel engine supply system is not tightly fixed, the needle valve of the fuel injection nozzle is stuck, and the diesel in the fuel tank has been used up before shutdown. This allows air to enter the diesel engine's supply system. In this way, when the plunger of the injector enters the diesel oil, the air entering the oil circuit is compressed, and the oil pressure cannot be increased. When the plunger of the injector enters the oil, the air volume expands and affects the oil absorption. As a result, the amount of diesel oil supply is suddenly increased or decreased.


The inspection method for this kind of failure phenomenon is to loosen the bleed screw on the diesel filter, the air bleed screw on the fuel injection pump or the high pressure oil pipe on the fuel injection pump, and rotate the diesel engine. If there are bubbles coming out, which indicates that there is air in the diesel engine supply system. The treatment method is to tighten the oil circuit joints, then loosen the air bleed screw on the fuel injection pump, turn the crankshaft until there is no bubble in the oil, and turn on the machine after tightening the bleeder screw. If moisture is found in the diesel oil, the same method can be used to check the cause of the moisture in the diesel oil. Replace the diesel in the fuel tank as required.


If there is no mixture of air and moisture in the diesel oil, should continue to check whether the injector performance is good and the fuel supply and distribution time is proper.


The starting speed is normal, the cylinder is compressed well, but it does not catch fire and is smokeless. This is mainly caused by the lack of oil supply in the low-pressure oil circuit. At this time, the inspection is mainly carried out along the oil circuit, the fuel tank, the diesel filter, the fuel pump, and the fuel injection pump. Generally, the fault can be found out.


Poor diesel filtration or no regular replacement of diesel filter is the main cause for the blockage of the low pressure oil circuit and diesel filter. To judge whether the oil circuit or diesel filter is blocked, remove the fuel pipe of the diesel filter through the fuel injection pump. If there is a lot of diesel oil in the fuel tank and there is a lot or no outflow from the diesel filter, the diesel filter has been blocked. If the low-pressure oil supply is good, the causes of high-pressure and oil-free diesel engines are mostly due to the wear or improper assembly of the plunger parts in the fuel injection pump.


The starting speed is normal and the injection sound can be heard, but it can not start, which is mainly caused by poor compression of the cylinder.

For the diesel engine equipped with decompression mechanism, if the decompression mechanism is in a non-decompression position, the diesel engine can still be gently rotated by a hand crank, and if the resistance is not large, the air leakage of the cylinder can be determined.


After the air leakage in the intake valve or exhaust valve, the compression temperature and pressure of the cylinder are not high, and diesel is not easy to burn. The main reason for this kind of air leakage is that the valve clearance is too small, which makes the valve not close tightly. On the other hand, debris such as carbon deposits on the valve cone or valve seat can also cause the valve to close loosely. You can rotate the crankshaft during the inspection. If you hear "squeak, squeak" sounds in the air filter and the exhaust pipe, it means that the cylinder is leaking.


When turning the crankshaft, if there is a sound of air leakage at the joint surface of the cylinder head and the cylinder block, it means that there is air leakage at the position of the cylinder pad. It may be that the cylinder head nut is not tightened or loose, or the cylinder gasket is broken.


When turning the crankshaft, there is a sound of air leakage inside the body or at the oil filler port. The cause is mostly on the piston ring. In order to find out whether the insufficient pressure in the cylinder is caused by the poor piston ring, a small amount of lubricating oil can be added to the cylinder. If the compression force in the cylinder is obviously increased after adding the oil, the surface piston wears too much, making the gap between the cylinder and the piston ring too large, and air leaks into the crankcase between the piston ring and the cylinder liner.


If the compression force does not change much after the engine oil is added, it indicates that the lack of compression force in the cylinder has nothing to do with the piston, and it may be that air leaks through the intake valve or exhaust valve.


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