🔍 Key Concepts

• Boundary lubrication and metal-to-metal contact in diesel engines • How solid particles and chemical contaminants interact with metal surfaces • The combined effect of abrasion, corrosion, and oxidation on wear

💭 Think About

• Ask yourself which of these contaminants can actually remove metal from surfaces, either by scratching (mechanical action) or eating away the metal (chemical action). • Consider whether only one type of contaminant is harmful, or if several of them might act together to increase wear. • Think about what happens to hot engine parts when exposed to acids and oxidation products inside a thin oil film.

✅ Before You Answer

• Verify which choices directly cause abrasive wear (scratching, scoring) of metal surfaces. • Verify which choices can lead to corrosive wear or surface pitting of bearings and liners. • Before picking an answer, check whether more than one listed contaminant is clearly capable of increasing metal wear rate in a diesel engine.