Causes of Engine Runaway in Diesel Generators

The operation of diesel generators can be fraught with risks if not managed properly. One such risk is the "runaway" phenomenon, which can lead to severe mechanical damage and safety hazards. This condition typically arises from malfunctions in the fuel supply system, governor, or other critical components. This article will delve into the primary causes of the runaway phenomenon and offer corresponding preventive and responsive measures to ensure the safety and stable operation of diesel generators.

Causes of the Runaway Phenomenon

 
The term "runaway" in the context of diesel generators refers to a situation where the engine speed uncontrollably increases beyond 110% of its rated speed during operation, accompanied by a loud noise. In such a state, the diesel generator's speed rises sharply, potentially exceeding the normal operating speed significantly within a very short time, which can lead to mechanical damage or even dangerous accidents.

1. Stuck Fuel Quantity Adjustment Lever

 
When the fuel quantity adjustment lever of the fuel pump is stuck at the maximum or near-maximum fuel position, the diesel generator cannot automatically reduce the fuel supply after starting, leading to a rapid increase in speed and potentially triggering a runaway. If the fuel quantity adjustment lever is stuck during the operation of the diesel generator, the speed will also rise sharply when the load is reduced or removed, causing a runaway.

2. Improper Assembly of Plunger

 
If the assembly of the fuel pump plunger and plunger sleeve is incorrect or stuck, it will prevent the fuel quantity adjustment lever from moving. This issue hinders the fuel pump from automatically adjusting the fuel supply according to load changes, thereby causing a runaway. Ensuring the precision fit between the plunger and sleeve during the assembly of the fuel pump is crucial for maintaining its normal function.

3. Detachment of Connecting Parts

 
If the connecting parts between the fuel quantity adjustment lever and the governor lever become detached, or if the screws on the lever fall off, the governor will not function properly. When the diesel generator's load decreases, the governor cannot automatically reduce the fuel supply, which may lead to a runaway. Ensuring that all connecting parts and screws are tightened and intact is a basic requirement for maintaining the governor's normal function.

4. Improper Governor Adjustment

 
If the adjustment of the fuel pump governor is improper, or if the highest speed limit screw is loose, the diesel generator may exceed its rated speed and fail to automatically reduce the fuel supply. When the speed reaches a runaway state, the system may not be able to completely stop the fuel supply, leading to a runaway. Regularly checking and adjusting the governor settings and ensuring the solidity of the limit screws are important measures to prevent a runaway.

5. Governor Flyweight Failure

 
If the governor flyweights become loose, break, or get stuck, or if the flyball (steel ball) bracket is damaged or the flyball falls off, it can lead to a runaway. The flyweights and flyballs are important control components in the governor, and their normal operation is essential for maintaining a stable speed. Therefore, regularly checking the condition of these parts and ensuring their normal operation is a necessary step to prevent a runaway.

6. Neglect of Maintenance

 
If a diesel generator is left idle for too long and not properly maintained, some control parts of the fuel pump and governor may rust in place at a high fuel supply position. When the diesel generator is restarted, the speed may rise sharply, leading to a runaway. Ensuring regular maintenance and upkeep of the diesel generator, especially after a long idle period, and checking and cleaning the control parts of the fuel pump and governor can effectively prevent this issue.

Emergency Shutdown Measures

 
In the event of a runaway phenomenon in a diesel generator, immediate emergency shutdown measures should be taken to prevent mechanical damage and safety hazards. The following are common emergency shutdown methods.

1. Cutting Off Air Supply

 
Interrupt the air supply to the combustion chamber. If the diesel generator's intake manifold is equipped with a valve, it can be closed immediately. Another method is to remove the upper part of the air filter and block the diesel generator's air intake with a cushion, fine cotton cloth, or similar material, forcing the diesel generator to "suffocate" and shut down. The effectiveness of this method depends on the sealing of the intake system, ensuring that the system joints are well sealed to prevent air leaks.

2. Decompression

 
Destroy the combustion conditions in the cylinder. This can be done by pulling down the decompression lever, keeping some valves open, preventing the mixture in the cylinder from being compressed, and thus stopping the diesel generator from operating. This method is suitable for diesel generators with a decompression function.

3. Cutting Off Fuel Supply

 
Interrupt the fuel supply of the diesel generator. Quickly retract the throttle and pull the hand throttle to the "shut down" position; if the plunger adjustment lever of the fuel pump is exposed, it can be manually pulled to the shut-down position; quickly loosen or break the high-pressure oil pipe. Due to the inertia of the crankshaft and piston, the effect of cutting off the fuel supply is relatively slow, but it can be used as a supplementary measure when other methods are ineffective.
 
The runaway phenomenon in diesel generators is a serious fault that requires timely identification of the cause and effective emergency shutdown measures. By proper maintenance and timely troubleshooting, the frequency of runaways can be reduced, ensuring the safe operation of diesel generators. In practical operations, appropriate emergency shutdown methods should be chosen based on the specific model and on-site conditions to ensure safety and equipment protection.