🔍 Key Concepts

• Crankcase explosions on large diesel engines often occur in two stages: a primary (initial) explosion and a possible secondary explosion. • What happens to pressure and air flow when crankcase doors or relief valves open or blow off after an explosion. • How oil mist, hot spots, and re‑admission of air can interact after the first explosion is vented.

💭 Think About

• After the initial explosion blows doors off, think about what happens next inside the crankcase: does pressure stay high, drop, or fluctuate? • Consider whether the first explosion removes or adds fuel/air mixture, and whether conditions for ignition might still exist afterward. • Ask yourself: which option describes a realistic physical consequence of venting an explosion in a confined space, especially concerning air flowing back in?

✅ Before You Answer

• Distinguish between engine overspeed causes (fuel/air to cylinders) and events limited mainly to the crankcase space. • Think about whether a fire in a damaged crankcase is more likely to be automatically extinguished or whether conditions could allow it to continue or re‑ignite. • Focus on the idea that when doors/relief valves open, crankcase pressure initially rises, then rapidly drops below or near atmospheric, and what that implies about air being drawn back in.