🔍 Key Concepts

• Air start systems on large two-stroke marine diesels and how starting air is admitted to cylinders • How crankshaft angle spacing between cylinders affects where torque can be applied • What it means to be able to turn the engine from any crank position in either direction (direct reversing)

💭 Think About

• Visualize the 8‑cylinder engine as 8 equally spaced positions around a circle (representing crank angles). How many of those positions must have starting air available so that, no matter where the crank stops, at least one cylinder is in a good position to receive starting air? • Consider that a two‑stroke engine has a power (and therefore good starting) stroke every revolution. How does that affect the needed distribution of air start valves compared with a four‑stroke? • Think about direct reversing: the engine must be able to start ahead or astern. How does that influence where air start valves must be placed to guarantee turning in either direction?

✅ Before You Answer

• Check the number of cylinders with start valves required to guarantee that for any crank angle, at least one cylinder is in a usable position for air admission. • Verify how the cylinders are phased around the crankshaft (equal angular spacing) and relate that to the answer choices. • Make sure your choice would still work if the engine stopped in the worst‑case crank position, and for starting in both ahead and astern directions.