Diesel Generator working principle; Four and two stroke Diesel Generator

Diesel Generator Working Principle and Four-Stroke Diesel Engine Explained

🔹 Introduction

A Diesel Generator (DG set) is a reliable source of electrical power that combines a diesel engine with an alternator to generate electricity. It is widely used as a backup power source during grid failures and as a prime mover in remote areas where electricity supply is unavailable.

A DG set typically consists of:

• Diesel engine – acts as the prime mover.

• Alternator – converts mechanical energy into electrical energy.

• Fuel system – stores and supplies diesel.

• Cooling & exhaust system – prevents overheating and removes gases.

• Control panel – monitors and regulates operation.

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🔹 Working Principle of a Diesel Engine

The diesel engine in a generator works on the principle of compression ignition. Unlike petrol engines that use spark plugs, a diesel engine compresses air to very high pressure and temperature:

• Compression ratio: 14:1 to 25:1

• Temperature range: 700–900°C

At this stage, diesel fuel is injected into the cylinder. Due to high temperature, the fuel ignites spontaneously, producing power.

That is why a diesel engine is also called a Compression Ignition (CI) Engine.

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🔹 Types of Diesel Engines in DG Sets

Diesel engines used in DG sets are generally classified into:

1. Two-Stroke Diesel Engine – Produces power every revolution of the crankshaft. More compact, but less efficient and higher maintenance.

2. Four-Stroke Diesel Engine – Produces power every two revolutions. More fuel-efficient, durable, and widely used in DG sets.

👉 Most DG sets use the four-stroke diesel engine due to better performance and reliability.

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🔹 Four-Stroke Diesel Engine Working Cycle

A four-stroke diesel engine completes one cycle in four piston strokes (two crankshaft revolutions).

1. Induction Stroke

• The inlet valve opens and the piston moves downwards, drawing in fresh air into the cylinder.

2. Compression Stroke

• Both valves close.

• The piston moves upwards, compressing the air to up to 25 bar, raising temperature to 700–900°C.

3. Ignition & Power Stroke

• Diesel fuel is injected at high pressure.

• Due to high temperature, the fuel self-ignites, creating an explosion.

• The piston is forced downwards, producing the power stroke.

4. Exhaust Stroke

• The exhaust valve opens, and the piston moves upwards, pushing out the burnt gases.

👉 Note: Power is developed only during the power stroke, which is why multi-cylinder engines are used for smoother operation.

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🔹 Why Multi-Cylinder Engines?

A single-cylinder four-stroke engine cannot supply continuous power efficiently. To overcome this, DG sets use multi-cylinder engines where crankshafts are staggered, ensuring smooth and balanced power delivery.

Common cylinder configurations include:

• In-line (4 or 6 cylinders) – simple and widely used.

• V-type – compact, used for higher power.

• Horizontally Opposed (Boxer) – stable and vibration-free.

• Radial – less common, used in aviation/marine engines.

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🔹 Applications of Diesel Generators

Diesel generators are essential in areas where continuous or emergency power is critical, such as:

• Hospitals and data centers – backup for critical operations.

• Industries and manufacturing plants – prevent downtime.

• Construction and mining sites – prime power in remote areas.

• Marine and defense applications – reliable power source.

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🔹 Advantages & Limitations

✅ Advantages

• High efficiency and fuel economy.

• Durable and long service life.

• Capable of handling heavy loads.

• Reliable for both prime and standby power.

❌ Limitations

• Higher noise and vibration compared to alternatives.

• Requires regular maintenance.

• Produces emissions, needs exhaust treatment.

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🔹 Conclusion

A Diesel Generator (DG) is a robust and reliable solution for both backup and prime power applications. Powered by a four-stroke compression ignition engine, DG sets provide efficient and durable operation. The choice of engine configuration and capacity depends on the load requirement, application, and fuel availability.

Despite some limitations, DG sets remain one of the most trusted sources of power supply across industries, commercial facilities, and remote locations.

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