🔍 Key Concepts

• Opposed-piston engine construction – how many pistons and where the cylinder heads are (or are not) • Difference between two-stroke and four-stroke diesel engine cycles • Meaning of single-acting vs double-acting in reciprocating engines

💭 Think About

• Think about how an opposed-piston engine is arranged: does it have one piston per cylinder or two? Where is the combustion space formed? • In an opposed-piston design, does the piston get pressure on one side of the crown or on both sides during the power-producing part of the cycle? • Consider how scavenging and exhaust usually work in opposed-piston diesels: is that more practical in a two‑stroke or a four‑stroke layout?

✅ Before You Answer

• Be clear on the definition: single-acting means only one face of the piston is used for doing work; double-acting uses both faces. • Verify whether typical opposed-piston marine diesels use valves in a cylinder head or ports in the cylinder wall for scavenging and exhaust. • Match the likely scavenging method (ports uncovered by pistons) with whether the engine is two-stroke or four-stroke before picking an answer.