Introduction

The spark plug is one of the most important components of an internal combustion engine. It plays a key role in igniting the air–fuel mixture in petrol engines, which helps start and run the engine efficiently. Without a properly working spark plug, your vehicle’s performance, fuel economy, and power output can drop significantly.

What is a Spark Plug?

A spark plug is a small electrical device fitted in the cylinder head of a petrol engine. It delivers electric current from the ignition system to the combustion chamber, where it creates a spark that ignites the compressed air–fuel mixture.

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Main Parts of a Spark Plug

1. Terminal
   The upper part where the ignition cable is connected. It carries high voltage from the ignition coil to the spark plug.
2. Insulator
   Made of porcelain or ceramic, it provides electrical insulation and helps the spark plug withstand high temperatures and voltages.
3. Metal Shell (Body)
   The metal casing that holds the insulator and provides a thread for fitting into the engine cylinder head.
4. Gasket or Washer
   Ensures gas-tight sealing between the plug and the combustion chamber to prevent leakage.
5. Center Electrode
   Connected to the terminal through a conductor. It emits the spark that ignites the air–fuel mixture.
6. Ground Electrode (Side Electrode)
   Attached to the metal shell. It is placed near the center electrode to create a small gap where the spark jumps.
7. Spark Gap
   The space between the center and ground electrodes. The spark occurs across this gap to ignite the mixture.

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Working of Spark Plug

1. When the piston compresses the air–fuel mixture in the combustion chamber, the ignition system sends a high voltage current (about 20,000 to 40,000 volts) to the spark plug.
2. The current travels through the terminal → center electrode → spark gap.
3. As the voltage crosses the spark gap, it ionizes the air particles and creates a spark.
4. This spark ignites the air–fuel mixture, causing a controlled explosion.
5. The explosion pushes the piston downward, producing the power stroke that turns the engine crankshaft.

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Functions of Spark Plug

• To ignite the air–fuel mixture in the engine cylinder.
• To remove heat from the combustion chamber (acts as a heat exchanger).
• To help maintain consistent engine performance and fuel efficiency.

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Types of Spark Plugs

1. Hot Spark Plug – Retains more heat and is used in low-speed engines.
2. Cold Spark Plug – Transfers heat quickly and is used in high-speed or high-performance engines.

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Maintenance Tips

• Clean or replace spark plugs after 10,000–15,000 km.
• Check for carbon deposits or oil fouling.
• Ensure the spark gap is set according to manufacturer specifications.
• Use recommended spark plug grade for your vehicle.

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Conclusion

The spark plug is small but crucial for smooth engine operation. Regular inspection and timely replacement can improve fuel efficiency, engine performance, and emissions. A healthy spark plug means a healthy engine.