Diesel engine runaway in generator sets is a severe mechanical failure, comparable in risk to an aircraft engine malfunction. As a power equipment engineer with 15 years of experience, I will analyze this phenomenon in depth, drawing from multiple accident cases.
1. Fatal Failures in the Fuel Supply System
In a 2020 incident at a data center, a backup diesel generator experienced a runaway condition. A teardown revealed that the fuel injection pump’s control ring had seized at maximum fuel delivery. Such mechanical sticking often originates from three key factors: first, abnormal wear of the plunger due to contaminated lubricating oil; second, rust adhesion caused by water contamination in the fuel; and third, improper O-ring replacement during maintenance, leading to abnormal clearance. A more concealed cause is the blockage of the fuel return line, which results in a continuously rich air-fuel mixture, effectively injecting a “stimulant” into the engine.
2. Failure Mechanisms in the Speed Control System
Traditional mechanical governors may seem simple but can be deadly. A lesson learned from a shipboard generator runaway during a typhoon showed that fatigue fractures in the governor spring often start with microscopic crack propagation. Electronic speed control systems are even more insidious—one power plant case revealed that oxidation in a speed sensor connector led to signal drift. The ECU misinterpreted the data, continuously increasing fuel delivery, and within just seven seconds, the engine exceeded its safety threshold.
3. Mysterious Negative Feedback in the Combustion Chamber
A 2018 mining accident revealed that excessive piston ring wear, allowing engine oil intrusion to reach 15% of the fuel volume, resulted in a self-sustaining oscillation. The fluctuating heat value from this mixed combustion caused the governor to enter a vicious cycle of “misjudgment-correction-overcompensation,” ultimately surpassing control limits.
4. The Turbocharger’s Role in Aggravating the Situation
The turbo lag effect in modern high-pressure common-rail diesel engines can lead to disaster. During a hospital backup generator test, transient conditions caused a delay in turbocharger response, momentarily disrupting the air-fuel ratio. The ECU, compensating based on a MAP table, inadvertently created a positive feedback loop as exhaust energy accumulated. Within 30 seconds, the engine speed surged to 180% of its rated value.
5. Environmental Factors as Catalysts
In an incident at a power substation along the Qinghai-Tibet Railway, the high-altitude (4,000 meters) environment caused dynamic imbalance in the centrifugal weights of the mechanical governor due to changes in air density. Meanwhile, low temperatures (-30°C) increased the governor oil viscosity by three orders of magnitude, completely disrupting the governor’s dynamic response characteristics.
Preventive Measures and Systematic Defense
A multi-layered defense system is necessary:
- Implement dual-redundant speed sensing systems.
- Install mechanical overspeed cutoff valves.
- Conduct step response testing regularly.
- Perform dynamic calibration of the governor every 500 operating hours.
- Use a laser alignment instrument to check transmission system coaxiality.
- Simulate sensor failures to validate failure modes in electronic control systems.
Such complex failures, involving multi-physics coupling, demand a systems-thinking approach from engineers. A real-time monitoring matrix with 20 critical parameters should be established. If any five of these parameters exhibit correlated deviations, a graded protection mechanism should be triggered immediately. Only by integrating mechanism research, intelligent monitoring, and mechanical safeguards can we effectively curb such “power runaway” incidents.