🔍 Key Concepts

• Effect of supercharging on cylinder pressure, temperature, and air mass flow in a four-stroke diesel • Purpose of valve overlap and how it changes with increased intake manifold pressure • Relationship between intake valve opening/closing timing and exhaust scavenging in supercharged vs naturally aspirated engines

💭 Think About

• How does increased intake manifold pressure from supercharging affect the best time to start letting air into the cylinder? Should it generally be earlier or later than on a naturally aspirated engine? • With higher intake pressure, what happens during the overlap period when both intake and exhaust valves are open? Would you want more or less overlap to help scavenging without blowing fresh charge straight out the exhaust? • Think about whether you want to keep exhaust in the cylinder longer or clear it out sooner when you now have a denser, pressurized intake charge.

✅ Before You Answer

• Compare options that advance intake opening versus those that retard intake opening and ask which makes better use of boost pressure. • Check which options increase or decrease valve overlap (intake early + exhaust late = more overlap; intake late + exhaust early = less overlap) and consider what a turbo/supercharged engine usually needs. • Verify which timing change would most improve cylinder filling and scavenging at higher pressures without excessively increasing pumping losses.