🔍 Key Concepts

• two-stroke vs four-stroke cycle timing (how often each has a power stroke and exhaust event) • scavenging and supercharging in two-stroke diesels (flow of air through the cylinder and its effect on temperature) • mean effective pressure (M.E.P.) and what it really measures (pressure/work, not directly temperature)

💭 Think About

• Think about when and how the exhaust leaves the cylinder in a two-stroke compared to a four-stroke at the same load. How does extra scavenging air affect exhaust gas temperature? • Consider what M.E.P. represents. Does a higher or lower M.E.P. automatically mean hotter or cooler exhaust, or is M.E.P. more about work per cycle? • Which option describes an actual temperature-changing process (like adding cooler air or changing timing) versus just a general engine characteristic?

✅ Before You Answer

• Be sure you understand that M.E.P. is an average pressure related to work, not a direct cause of gas temperature changes by itself. • Review how scavenging air flows in a two-stroke with a turbine-driven supercharger and whether that tends to cool or heat the exhaust gases. • Check which choice correctly describes valve/port timing in a two-stroke vs a four-stroke; eliminate any option that gets the timing relationship backwards.