In diesel engines, which ignition method is used?

• A. Spark ignition
• B. Compression ignition
• C. Electric glow ignition
• D. Induction ignition

Answer: (B)

Diesel engines rely on compression ignition. The incoming air is compressed to a very high pressure, which raises its temperature to a level that can ignite fuel on contact. Diesel fuel is injected into this hot, compressed air and begins to burn without a separate spark plug. This is different from spark-ignition engines, like many gasoline engines, where a spark plug provides the energy to ignite a premixed air–fuel charge at a much lower compression. Glow plugs can help warming the chamber for starting in cold conditions, but they don’t provide the primary ignition in normal operation. Induction ignition isn’t used as the main method in diesels.