MCQ Detailed View

Engines require a method to ignite the fuel-air mixture to produce power. In a petrol (gasoline) engine, ignition is achieved with the help of spark plugs that generate a spark to ignite the compressed mixture. However, diesel engines work on a different principle, known as compression ignition, and therefore do not use spark plugs at all.

In a diesel engine, only air is drawn into the cylinder and is compressed to a very high pressure, causing its temperature to rise significantly. At the end of the compression stroke, diesel fuel is injected directly into this hot, compressed air. The high temperature causes the fuel to ignite spontaneously, without the need for an external spark. This process is called auto-ignition.

The design difference is the reason why a diesel engine requires 0 spark plugs. Instead of spark plugs, diesel engines are equipped with fuel injectors, which spray fine droplets of diesel into the combustion chamber. In very cold conditions, glow plugs may be used in some diesel engines to preheat the air and aid ignition, but they are not the same as spark plugs.Reviewing the options:

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  2, 3, or 4: Incorrect, as no spark plugs are used at all.

  
  


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  0: ✅ Correct, since diesel ignition occurs by compression and heat.

  
  


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  None of these: Incorrect, as 0 is the right choice.

  
  

Thus, a diesel engine does not need spark plugs because it relies on heat from compressed air to ignite the fuel, making it different from petrol engines in operation and design.