🔍 Key Concepts

• Valve timing in a four-stroke diesel engine (intake, compression, power, exhaust) • Purpose of opening exhaust valves early relative to piston position and port uncovering • Difference between pumping losses and back pressure in an engine

💭 Think About

• Think about what happens inside the cylinder just before the intake ports/valves open: what is the pressure, and what is the exhaust trying to do? • If exhaust gases are cleared more effectively before intake begins, which statement (I or II) does that mainly affect, and how? • Does opening the exhaust valve earlier make it easier or harder for the piston to move during the exhaust stroke?

✅ Before You Answer

• Be clear on what pumping losses are: extra work the piston must do to push gases in or out of the cylinder • Be clear on what back pressure is: resistance to flow in the exhaust system that opposes gas leaving the cylinder • Check whether early exhaust opening mainly changes the work done by the piston or the resistance in the exhaust system itself