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Operation and Maintenance of Diesel Generators – Part 8: Frequently Asked Interview Questions on Diesel Generators (Ideal for Job Interviews)

Part 8: Frequently Asked Interview Questions on Diesel Generators (Ideal for Job Interviews)

In this final part of the Operation and Maintenance of Diesel Generators Series, we address some of the most common questions regarding Diesel Generators (DG). These frequently asked questions (FAQs) cover a range of topics from operational issues and maintenance procedures to engine performance and troubleshooting. Understanding these FAQs is crucial for operators to ensure smooth and efficient operation, prevent common problems, and maintain the longevity of their DG sets.

Whether you are a seasoned professional or new to the world of diesel generators, this section will provide clarity on essential topics like fuel system issues, smoke colors, oil pressure concerns, and DG shutdowns. By addressing these concerns, we aim to provide you with the tools and knowledge needed to keep your DG set running at its best.

If you haven’t read the previous parts, check them out here:

Part 1: Operation and Maintenance of Diesel Generators – Part 1: Understanding Diesel Engine, Its Working Principle and Key Components

Part 2: Operation and Maintenance of Diesel Generators – Part 2: Understanding Alternator, Its Components, and Working Principle

Part 3: Operation and Maintenance of Diesel Generators – Part 3: Understanding Starting system and Lubrication system of Diesel Generators

Part 4: Operation and Maintenance of Diesel Generators – Part 4: Understanding Fuel System and Air System of Diesel Generators

Part 5: Operation and Maintenance of Diesel Generators – Part 5: Understanding Cooling System of DG, Its Working Principle and Key Components

Part 6: Operation and Maintenance of Diesel Generators – Part 6: Understanding A-Check, B-Check, C-Check, and D-Check for Diesel Generators

Part 7: Operation and Maintenance of Diesel Generators – Part 7: DG Starting Procedures, Do’s & Don’ts, and DG Efficiency Calculations

Frequently Asked Interview Questions

1. Why should a DG set not be run with a full fuel tank?

Answer: A fully filled fuel tank can create improper pressure

across the fuel lines, leading to incomplete combustion, which can cause a large amount of black smoke emission.

2. Why is bleeding required?

Answer: Air bleeding is required under the following circumstances:

  • When the engine has not been operated for a long time.

  • After replacing a fuel filter or element.

  • If the engine was started without opening the fuel cock and ran for some time.

  • When the feed pump is not working properly.

  • If there is leakage from fuel pipes or filters.

3. How to remove an air lock in the fuel system?

Answer: Air lock can be removed by following these steps:

  • Loosen the bleeding screw of the primary fuel filter.

  • Unscrew the priming knob of the fuel pump and move it up & down at least 10 to 15 times until the fuel flows without air bubbles.

  • Tighten the air vent screw after bleeding.

  • Repeat the same steps for the secondary fuel filter.

  • Finally, loosen the air vent screw of the fuel injection pump and bleed out any remaining air bubbles.

4. What is Thin Film Lubrication?

Answer: Thin Film Lubrication occurs between piston rings and the cylinder liner, reducing metal-to-metal contact, friction, and wear of metal parts.

5. What is the function of a thermostat?

Answer: The thermostat regulates engine temperature by cutting the engine supply if the temperature increases or decreases beyond a specified limit.

6. What is the function of a thermostat valve?

Answer:

  • When the coolant temperature is low, the thermostat valve remains closed, and coolant flows through the bypass passage to the water pump.

  • When coolant temperature exceeds 90°C, the thermostat fully opens, bypass passage closes, and coolant passes through the radiator for cooling.

7. Why should the radiator cap not be opened when hot?

Answer:

  • The radiator cap contains pressure-regulating elements.

  • Loosening the cap disrupts the cooling system pressure, leading to boiling over and possible DG set damage.

8. What is over-speeding in a DG set?

Answer:

  • Over-speeding occurs when the engine speed increases suddenly due to:

    • Load disconnection from the DG.

    • Load imbalance on the DG.

  • This can cause the alternator to exceed its safe speed limit, leading to alternator winding burn-out.

9. What causes Black Smoke in a DG set?

Answer: Black smoke indicates improper combustion, which can be due to:

  • Clogged or incorrect air cleaner.

  • Defective fuel injection system.

  • Blocked exhaust system or improper exhaust piping.

  • Engine overload or electrical short circuit on the load side.

10. What causes Blue Smoke in a DG set?

Answer: Blue smoke is emitted when oil burns in the combustion chamber due to:

  • Excess oil in the sump.

  • Excess lubricating oil pressure.

  • Worn piston rings and liners.

  • Worn valve stem and valve guides.

11. What causes White Smoke in a DG set?

Answer: White smoke indicates the presence of water in the combustion chamber, which can be caused by:

  • Cracked cylinder head.

  • Cracked or damaged liner.

  • Water contamination in diesel.

  • Damaged cylinder head gasket.

  • Water in the combustion chamber (dangerous as it can lead to hydraulic lock and severe engine damage).

12. Why does the DG set shut down immediately after starting?

Answer: Possible reasons include:

  • Low oil pressure or high coolant temperature.

  • Fault in fuel supply.

  • Air lock in the fuel system.

  • Failure in the engine control system.

13. Why is regular maintenance essential for a DG set?

Answer:

  • Ensures reliable operation.

  • Prevents unexpected breakdowns.

  • Improves fuel efficiency and engine lifespan.

  • Identifies potential issues early, avoiding costly repairs.

14. How often should engine oil be changed in a DG set?

Answer:

  • Change oil every 250 hours of operation or every 6 months, whichever is earlier.

15. What is the ideal coolant temperature for a DG set?

Answer:

  • The coolant temperature should be maintained between 75°C and 95°C for optimal performance.

16. What is the normal oil pressure in a DG set?

Answer:

  • At rated speed (105°C): 3 to 7 kg/cm².

  • At idle speed: 1 to 2 kg/cm².

17. What precautions should be taken while refueling a DG set?

Answer:

  • Do not overfill the fuel tank.

  • Ensure the engine is off before refueling.

  • Do not remove the fuel cap while the engine is running.

18. How is DG efficiency calculated?

Answer:

  1. Calculate Diesel Consumption (L).

  2. Calculate Diesel Output (kWh).

  3. Convert Diesel Consumption into BTU: (1L Diesel = 36500 BTU).

  4. Convert kWh into BTU: (1 kWh = 3413 BTU).

  5. Efficiency Formula:

    • Efficiency (%) = (Output BTU ÷ Input BTU) × 100.

Final Thoughts

This FAQ section provides a valuable reference for anyone working with Diesel Generator (DG) sets. By understanding the answers to common issues, operators can ensure reliability, prevent downtime, and maximize the efficiency of their DG sets. Regular maintenance and attention to operational guidelines will extend the life of your equipment and improve overall fuel efficiency and performance.

In case you have any other questions or if something is unclear, feel free to drop a comment below. We hope these insights have been helpful to you in understanding the intricacies of diesel generator operation and maintenance. Stay tuned for more technical content and detailed guides in future posts!

Have any questions or need further clarification? Don’t hesitate to ask. Share this article with colleagues or industry peers who might benefit from the insights provided.

Disclaimer
This article is for educational purposes only and has been compiled from various online sources. While every effort has been made to ensure accuracy, readers should refer to manufacturer guidelines and industry experts for specific operational and maintenance instructions.
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