In a diesel cycle engine, ignition is achieved by which mechanism?

• A. The diesel cycle depends on high compression pressures to ignite the air-fuel charge in the cylinder.
• B. Spark plug ignition.
• C. External flame.
• D. Battery ignition.

Answer: (A)

Compression-ignition is the mechanism. In a diesel engine, air is compressed to a very high pressure, heating it to a temperature high enough to ignite the fuel on contact. Diesel fuel is injected into this hot, compressed air and auto-ignites without any spark or external flame. That’s why diesel engines don’t use spark plugs or external ignition sources. Spark plug, external flame, or battery ignition are features of spark-ignition systems, not diesel’s compression-ignition process.