Diesel generator sets can operate under no-load conditions, but strict operational guidelines and time control must be followed; otherwise, irreversible damage may occur.
I. Technical Characteristics of No-Load Operation
Combustion System Imbalance
The optimal combustion condition for diesel engines is within the 50-75% load range. Under no-load conditions, the fuel injection volume is only 20-30% of full load. Experimental data shows that under no-load operation, the cylinder temperature drops by 200-300°C compared to normal operation, leading to an increase of over 35% in fuel atomization particle diameter and an increase of 400 ppm in unburned hydrocarbon emissions.
Lubrication System Abnormalities
When operating at low speeds under no-load conditions (<1000 rpm), the main oil passage pressure drops to 1.5-2.0 bar (normal range: 2.5-3.5 bar), and the oil film thickness at the crankshaft journal decreases to 3-5 μm (normal range: 8-12 μm), intensifying component wear under boundary lubrication conditions.
II. Five Major Hazards of Prolonged No-Load Operation
- A marine diesel generator set (Model: 8L21/31) ran continuously under no-load conditions for 120 hours, resulting in a carbon deposit thickness of 2.3 mm on the turbocharger and an 18% reduction in boost efficiency.
- Maintenance records indicate that long-term no-load operation caused cylinder liner out-of-roundness to exceed 0.15 mm (standard: ≤0.03 mm).
- A backup generator set in a data center experienced frequent no-load starts, leading to three starter motor brush replacements within six months.
- Laboratory tests show that continuous no-load operation for four hours increased engine oil acidity by 0.8 mgKOH/g (new oil standard: ≤1.0 mgKOH/g).
- Control module statistics of a certain generator model reveal that equipment with more than 30% no-load operation time had a 40% shorter overhaul cycle.
III. Scientific Operating Guidelines
Time Control
- No-load warm-up after a cold start: ≤5 minutes (ambient temperature >0°C)
- Routine no-load test run: Single session ≤15 minutes, monthly total ≤60 minutes
- No-load cooling before shutdown after load operation: 3-5 minutes
Load Management Techniques
- Install virtual load devices (recommended power ≥30% of rated load).
- Use intelligent paralleling systems for automatic load distribution.
- Equip automatic unloading devices (response time <200 ms).
Enhanced Maintenance Measures
- Increase engine oil sampling frequency after no-load operation (every 50 hours).
- Use low-ash engine oil (ash content ≤0.8%).
- Perform maintenance operation at 80% load for 1 hour every 200 hours.
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