🔍 Key Concepts

• compression ignition in diesel engines • relationship between compressed air temperature and fuel ignition • difference between diesel (compression-ignition) and gasoline (spark-ignition) engines

💭 Think About

• Think about what happens to the temperature of a gas when it is compressed in a cylinder without cooling. • In a diesel engine, when is the fuel actually injected: before compression, during compression, or after the air is compressed? How does that relate to ignition? • Which of the choices describes a primary design function of compression, rather than a side effect or a later part of the cycle (like exhaust)?

✅ Before You Answer

• Recall that in a diesel engine there is no spark plug; how then is the fuel ignited? • Identify which option directly depends on high temperature from high compression, not on timing terms like "lag" or "delay". • Eliminate any choices that refer to processes that happen after combustion, rather than during the moment of ignition.