🔍 Key Concepts

• Diesel engine combustion and what proper combustion looks like in terms of exhaust color • What causes unburned fuel versus unburned lube oil in the exhaust • How air-to-fuel ratio (too much air or too little air) affects exhaust color

💭 Think About

• Think about what happens if the fuel in a diesel cylinder does NOT fully ignite or burns at too low a temperature—what would that look like in the exhaust? • Which condition would make the mixture too ‘cold’ or too ‘lean’ so that droplets or vapor are visible as light gray or whitish smoke? • Which option would most likely cause fuel to pass through the cylinder partially unburned rather than burned completely to clear gas?

✅ Before You Answer

• Compare light gray/whitish smoke to blue smoke (often oil) and black smoke (often overload/too much fuel). Which choice best matches light gray? • Ask: Does excess combustion air tend to clean up the exhaust (more complete burn) or make it smokier? • Ask: Would high compression temperature make combustion more complete (less visible smoke) or less complete (more visible smoke)?