🔍 Key Concepts

• diesel combustion and what complete combustion should look like at the exhaust • the role of air supply vs. fuel supply in forming smoke • how air intake restriction changes the fuel/air mixture

💭 Think About

• Think about whether black smoke usually means there is too much fuel or too little air for the amount of fuel being injected. • Consider which option would most likely make the mixture "rich" (more fuel than the available oxygen can burn). • Ask yourself which condition would reduce the amount of air getting into the cylinders while the fuel system continues to inject the same amount of fuel.

✅ Before You Answer

• Recall that normal, efficient diesel combustion should produce little visible smoke at steady load. • Link black smoke with carbon/soot from unburned fuel, and decide which choice best creates that condition. • Eliminate any options that would more likely cause white or bluish smoke instead of black.