🔍 Key Concepts

• Compression ratio in a diesel or gasoline engine and how it affects air temperature during compression • The basic gas law relationship between pressure, temperature, and volume (P-V-T) for a gas being compressed • What happens to the air in a cylinder when the piston moves up on the compression stroke

💭 Think About

• When you compress a gas into a smaller volume, what generally happens to its temperature if no heat is lost to the surroundings? • In an internal combustion engine, why is a certain minimum temperature needed at the end of compression, especially in a diesel engine? • Think about cause and effect: does the compression ratio depend on the temperature, or does the temperature result from the compression ratio?

✅ Before You Answer

• Make sure you know that compression ratio is defined as the ratio of cylinder volume at bottom dead center to volume at top dead center. • Recall that for a gas, if volume goes down quickly and significantly, temperature tends to go in a specific direction (up or down?). • Eliminate any choice where the cause–effect direction between temperature and compression ratio is reversed.