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Hazards of Diesel Generator Set Small Load

Aug. 25, 2018

Longer than 10 minutes of low idle speed or no load can damage the engine. Because the temperature of the combustion is so low that the fuel can not be completely burned. This will cause the formation of carbon deposition and valve adhesion around injector holes and piston rings. 

If the engine coolant temperature is below 60°C, the unburned fuel will wash away the lubricating oil on the cylinder wall and dilute the oil in the crankcase. Fuel diluents will affect the quality of lubricant and shorten the engine life. It’s better to shorten idle time to prevent this from happening.


Running diesel generator set under small load, with the continuation of running time, the following five hazards will occur.

1. Piston-cylinder liner seal is not good, oil channelling, entering to the combustion chamber to burn, exhaust blue smoke;

2. For turbocharged diesel engine, supercharging pressure is low due to low load and no-load. It is easy to cause the effect of turbocharger oil seal (non-contact type) seal to decline, oil moves into the pumping chamber, along with the intake into the cylinder;

3. A part of the oil in the cylinder takes part in the combustion, part of the oil cannot be completely burned, and the carbon deposits are formed at the valve, inlet, piston top, and piston ring, etc, and some are discharged with the exhaust. In this way, the cylinder sleeve exhaust duct will gradually accumulate oil, will also form a carbon deposit;

4. The supercharger indoor oil accumulates to a certain extent, it will leak out from the joint surface of the supercharger;

5. Running under small load for a long time will lead to more serious wear and serious of moving parts and deterioration of engine combustion environment, which will lead to the early overhaul period.

Therefore, the diesel engine manufacturers emphasize that the low load / no load operation time should be minimized in the use of both naturally aspirated and pressurized diesel engines, and the minimum load should not be lower than 25%-30% of the rated power of the genset.

Cummins diesel generator

Full load operation of diesel generating sets for a long time can not only improve the performance, find out the hidden dangers of safety, but also avoid major communication accidents.

First. Preparation before start-up

Check that the cooling water or antifreeze in the diesel engine tank is satisfied before starting, if it is lacking, then fill it up. Pull out the oil gauge to see if the lubricating oil is lacking, if it is missing, add it to the prescribed tick mark, and then carefully check whether the components have hidden trouble, if fault found to be timely troubleshooting before starting up.

Second. it is strictly forbidden to start diesel engine with load.

Before starting the diesel engine, you should pay attention to the output air switch of the diesel generator must be closed. After starting the diesel engine of the ordinary generator set, it will take 3-5 minutes of idle operation (about 700rpm/min), the winter temperature is low (700 rpm) and the idle running time should be extended for a few minutes. After starting the diesel engine, it is necessary to observe whether the oil pressure is normal and whether there is oil leakage, water leakage and other abnormal phenomena. (The oil pressure must be above 0.2MPa under normal conditions,) If abnormalities found, stop and overhaul the engine. If there is no abnormality, the diesel engine speed will be increased to the rated speed of 1500 RPM/min. At this time, the generator display frequency is 50Hz and the voltage is 400V, then the output air switch can be closed and put into use.

Generator sets are not allowed to run under no-load for a long time. Because long hours of no-load operation will cause the diesel fuel injected from fuel injector not to be completely burned, resulting in carbon deposits, valve and piston ring leakage. If it is an automatic generator set, there is no need for idle speed because the automatic unit is usually equipped with water heater, so that the cylinder block of the diesel engine is always kept at about 45 , and the diesel engine can transmit power normally within 8-15 seconds after starting.

Third. pay attention to observe the working state in operation.

During the operation of the generator set, specially-assigned person should be on duty to observe a series of possible faults, especially the changes of oil pressure, water temperature, oil temperature, voltage, frequency and so other important factors. In addition, it should be noted that there is sufficient diesel fuel in operation, such as fuel interruption in operation, which will objectively cause load shutdown, which may lead to the damage of generator excitation control system and related components.

Fourth, it is strictly forbidden to stop with load.

Before each shutdown, the load must be cut off step by step, the generator output air switch should be closed. Finally, the diesel engine should be slowed down to idle state for 3-5 minutes before stopping the engine.

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