🔍 Key Concepts

• Four-stroke diesel cycle timing: intake, compression, power, exhaust events and when valves normally open/close relative to TDC/BDC • Effect of supercharging on cylinder filling, scavenging, and the need for more/less valve overlap • How valve overlap (when intake and exhaust are open together) helps or hurts when intake air is under pressure

💭 Think About

• Think about what supercharging does to the intake manifold pressure: does it make it easier or harder to fill the cylinder quickly? How might that affect when you want the intake valve to start and stop opening? • Consider what happens near the end of the exhaust stroke and the start of the intake stroke. With pressurized intake air, would you want more time when both valves are open, or less? Which operations (advance/retard) increase overlap? • For each choice, ask yourself: does this change help blow fresh air into the cylinder and push exhaust out, or does it risk blowing exhaust back into the intake or losing too much fresh charge out the exhaust?

✅ Before You Answer

• For each option, identify whether valve overlap increases or decreases, and decide if that’s desirable with supercharging. • Check whether advancing or retarding the intake valve opening helps use the higher intake pressure to improve cylinder filling and scavenging. • Verify that the exhaust valve closing timing change in your chosen option would help clear exhaust gases while minimizing loss of fresh charge with boosted intake pressure.