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Diesel Generator Operation and Maintenance: Interview Questions and Answers

Introduction:
Diesel generators are vital backup power sources in facility management, ensuring seamless operations during outages. Proper maintenance, troubleshooting, and efficiency optimization enhance reliability and compliance with safety regulations. This guide covers essential best practices for diesel generator operation and preventive care to maximize performance.

Diesel Generator Question & Answer
1. Why should a DG set not be run with full fuel in the tank?
Answer: A full fuel tank creates improper pressure across fuel lines, leading to excessive black smoke emission.

2. Why is bleeding required?
Answer: The fuel system requires air bleeding under the following circumstances:
  • The engine has not been operated for a long time.
  • A fuel element has been replaced.
  • The engine was started without opening the fuel cock and has run for some time.
  • The feed pump is not functioning properly.
  • There is leakage from fuel pipes or fuel filters.
3. How to remove Air Lock?
Answer: Air lock can be removed using an air primer as per the steps below:
  • Loosen the bleeding screw of the primary fuel filter.
  • Unscrew the priming knob of the fuel pump, move it 10 to 15 times, until fuel flows out without air bubbles.
  • Tighten the air vent screw and repeat for the secondary fuel filter.
  • Finally, loosen the air vent screw of the fuel injection pump and remove air bubbles.
4. What is Thin Film Lubrication?
Answer: It is a lubrication layer between piston rings & cylinder liner, reducing metal to metal contact, friction, and wear of metal parts.

5. What is the function of a Thermostat?
Answer: The thermostat cuts the engine supply if the engine temperature increases or decreases beyond a safe level.

6. What is the function of a Thermostat Valve?
Answer: At low temperature, the thermostat valve remains closed, and coolant flows through the bypass passage to the cooling pump.
When coolant temperature exceeds 90°C, the thermostat fully opens, closing the bypass and allowing coolant to pass through the radiator.

7. Why should the radiator cap not be opened?
Answer: The radiator cap maintains the cooling system pressure. Loosening the cap can cause pressure imbalances harmful to the DG set.

8. What is Over Speeding?
Answer: Over speeding occurs when the load is suddenly removed or there is an imbalance in the load. This causes the engine speed to increase, leading to excessive alternator speed, which can burn alternator windings.

9. What causes Black Smoke?
Answer: Improper combustion due to:
  • Choked or incorrect air cleaner.
  • Defective fuel injection system.
  • Blocked exhaust system or incorrect exhaust piping.
  • Engine overload or electrical short circuit on the load side.
10. What causes Blue Smoke?
Answer: Blue smoke occurs when oil burns in the combustion chamber, due to:
  • Excess oil in the sump.
  • Excess lubrication oil pressure.
  • Worn piston rings & liners.
  • Worn valve stems & guides.
11. What causes White Smoke?
Answer: White smoke indicates water contamination in the combustion chamber, due to:
  • Cracked cylinder head.
  • Cracked or damaged liner.
  • Water diluted diesel or damaged cylinder head gasket.
  • Water presence, which may cause hydraulic lock and severe engine damage.
12. What are some best practices for operating a diesel generator efficiently?
Answer: To ensure efficient operation, follow these best practices:
  • Load Optimization – Run the generator at 70-80% of its rated capacity to avoid underloading issues like wet stacking.
  • Routine Exercising – Start and run the generator under load at least 30 minutes per month to prevent fuel deterioration and battery failure.
  • Warming Up & Cooling Down – Allow the engine to warm up before applying a load and cool down before shutdown to avoid thermal stress.
  • Maintain Clean Fuel – Ensure diesel fuel is filtered and free from water or sludge to prevent injector clogging.
  • Check for Leaks & Corrosion – Regularly inspect for oil, fuel, or coolant leaks and address corrosion in the alternator or exhaust.
13. Why is underloading a diesel generator a problem?
Running a diesel generator at low load (<30%) for extended periods can lead to wet stacking, where unburned fuel deposits accumulate in the exhaust, reducing efficiency and increasing emissions. It can also cause carbon buildup, leading to engine damage over time.

14. What are the common reasons a diesel generator fails to start?
A diesel generator may fail to start due to:
  • Dead or weak battery – Check charge levels and replace if needed.
  • Fuel system issues – Ensure sufficient fuel and check for clogged filters or air in fuel lines.
  • Low oil pressure shutdown – Top up oil to required levels.
  • Starter motor failure – Inspect electrical connections and solenoid function.
  • Faulty control panel – Check for alarms or error codes.
15. What could cause a diesel generator to overheat?
Overheating may occur due to:
  • Low coolant level – Refill coolant and check for leaks.
  • Clogged radiator or fan failure – Clean the radiator and inspect cooling fans.
  • Overloading – Reduce excessive load on the generator.
  • Thermostat failure – Replace a stuck or malfunctioning thermostat.
16. What should you do if a generator is producing excessive black smoke?
Black smoke indicates incomplete fuel combustion, often caused by:
  • Dirty air filter – Replace or clean the air filter.
  • Overloading – Reduce load to an optimal level.
  • Fuel injector issues – Inspect and clean injectors.
  • Poor quality fuel – Drain contaminated fuel and refill with clean diesel.
Final Thoughts
This Q&A set is designed to help facility managers, engineers, and technicians understand essential aspects of diesel generator operation, maintenance, troubleshooting, and compliance. Mastering these concepts ensures uninterrupted power supply, safety, and efficiency in facility management.

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