Diesel aero-engines can be expected to produce the same power as an Avgas engine when the diesel engine’s cylinder capacity is more than how many times larger than the Avgas engine’s capacity?

• A. More than twice the cylinder capacity
• B. About the same cylinder capacity
• C. Less than half the cylinder capacity
• D. Four times the capacity

Answer: (A)

Power output is tied to how much air-fuel mixture can be burned and how fast the engine can cycle that mixture. Gasoline (avgas) engines are usually designed for high RPM and deliver a high power per unit of displacement. Diesel engines, while efficient, typically operate at lower RPM and with heavier components, so their power density per litre is lower. To reach the same overall power as an avgas engine, the diesel must have a larger cylinder capacity because each unit of displacement contributes less power. In practice, you often need more than twice the displacement of the avgas engine to equal its power output, making the threshold “more than twice the capacity” the correct rule of thumb. The other options don’t fit because they imply similar or far smaller displacement adjustments, which wouldn’t reliably achieve the same power.