🔍 Key Concepts

• Diesel engine combustion process – how ignition happens without spark plugs • Effect of air compression on temperature and ignition delay • Relationship between injection delay and cylinder pressure/temperature

💭 Think About

• Ask yourself: In a diesel engine, what actually causes the fuel to ignite once it is injected? Is it compressed air, compressed fuel, or a spark? • Think about what happens to air when it is compressed in a cylinder – what changes (pressure, temperature, density) and how each of those might affect ignition delay. • Consider whether higher pressure & temperature in the cylinder before injection would tend to shorten the time between start of injection and start of combustion, or make no difference.

✅ Before You Answer

• Verify the primary reason diesel engines compress only air on the compression stroke instead of an air-fuel mixture. • Check how increased air temperature from compression affects the ability of fuel to auto-ignite once injected. • Confirm what injection delay means: the time between start of injection and start of combustion, and how cylinder conditions (pressure/temperature) influence that delay.