An engine that has one power stroke every two crankshaft revolutions is a:

• A. Two-Stroke Diesel Engine
• B. Four-Stroke Natural Gas Engine
• C. Two-Stroke Gasoline Engine
• D. Double-Acting Engine

Answer: (B)

The key idea is how often a power stroke occurs relative to crankshaft turns. In a four-stroke cycle, the piston goes through intake, compression, power, and exhaust across two full crankshaft revolutions, and the power stroke happens once per cycle. So you get a power stroke every two revolutions, which matches the description. The fuel type doesn’t change this timing, so a four-stroke engine using natural gas still has one power stroke every two turns. Two-stroke engines deliver a power stroke with every revolution, so they don’t fit. A double-acting design refers to how the piston produces work on both sides in some configurations, not to this two-revolution timing, so it also doesn’t fit. Hence, it’s a four-stroke engine.