Diesel engine runaway refers to the situation where the rotational speed loses control, sharply increasing to a level far beyond the rated speed, accompanied by severe vibrations and abnormal noises. If effective measures are not taken in time to stop the engine when it is running away, it can cause significant property damage and even casualties.
The main causes of diesel engine runaway are roughly as follows: a large amount of engine oil entering the cylinder for combustion; and excessive diesel supply. Although both cases result in the engine running at an abnormally high speed, there are differences. When engine oil enters the cylinder for combustion, blue smoke comes out of the exhaust pipe; when diesel engine runaway is caused by excessive diesel supply, thick black smoke comes out of the exhaust pipe.
1. Engine oil enters the cylinder and participates in combustion.
(1) Too much engine oil is added in the oil pan, and a large amount of oil passes through the gap between the cylinder liner and the piston and enters the cylinder for combustion.
(2) There is too much engine oil in the air filter, exceeding the scale line, and some of the oil directly enters the cylinder for combustion from the intake duct.
(3) The piston ring is worn out, and the effect of engine oil being pumped into the combustion chamber is strengthened.
(4) The oil ring and the oil return holes on the piston are blocked, causing the engine oil to remain in the cylinder for combustion.
(5) Diesel leaks into the oil pan, causing the oil level to rise, and the mixed oil enters the combustion chamber for combustion.
(6) The diesel engine is too hot, causing the engine oil to be too thin and easily entering the cylinder for combustion.
(7) The engine oil does not meet the usage requirements.
2. Excessive Diesel Supply
(1) The plunger is stuck at the maximum fuel supply position. The main reasons are: During the assembly of the plunger pair, the plunger was damaged; The tightening torque of the oil outlet valve was too large, causing the plunger sleeve to deform; The gasket of the plunger sleeve's positioning screw was too thin or was not installed properly, resulting in the deformation of the plunger sleeve; The position of the gear rod component and the regulating gear was installed wrongly.
(2) Possible reasons related to the governor: ① The plunger adjustment arm of the oil pump did not enter the lever fork of the governor, and the plunger was at the maximum fuel supply position; ② The pins and keys, etc., were loose; ③ The adjustment was improper; the preload of the regulating spring was increased randomly; ④ The device for adjusting the speed was adjusted to the extreme position; ⑤ When installing the governor ball bearing, too much lubricating grease was applied and it was too thick, making it difficult for the ball bearing to open when the speed increased.
(3) Excessive fuel supply was caused by quality problems of the fuel injector.
3. Measures to be taken after a runaway engine occurs
When a diesel engine experiences runaway, one must remain calm and composed. The first step is to assess the color of the exhaust smoke. If it is blue, measures such as blocking the intake pipe or opening the relief valve can be taken. Because cutting off the diesel fuel supply is ineffective at this time. If it is black smoke, the method of cutting off the diesel fuel supply can be used, that is, quickly loosen the connecting nut of the high-pressure fuel pipe; at the same time, block the intake pipe or open the relief valve. If it is a moving motor vehicle or a tractor in operation, when the diesel engine of such vehicles experiences runaway, if there are appropriate conditions, measures to increase the load of the diesel engine can be taken to force it to stop.
4. A simple and effective method for checking whether diesel fuel may be over-supplied.
Fix the throttle of the diesel engine at the off position, then rotate the engine. If there is still fuel supply, it may cause runaway. You need to conduct an inspection until the fault is resolved before it can be used normally.