Why shouldn't MOGAS be used in aviation engines?

• A. MOGAS is not compatible with aviation engines.
• B. Aviation engines have higher compression ratio engines.
• C. MOGAS contains additives that could harm the engine.
• D. MOGAS cannot be pumped by aviation fuel systems.

Answer: (B)

The key idea is the need for fuel that resists knocking in high‑compression engines. Aviation piston engines operate at higher compression ratios, which raises the temperature and pressure just before ignition. If the fuel can’t withstand that pressure without auto-igniting, you get detonation (knock), which can damage the engine. MOGAS (automotive gasoline) generally does not provide the same anti-knock performance as aviation gasoline and is not formulated for aircraft service, so using it increases the risk of knocking under flight operating conditions.

The other options are less precise: while MOGAS may have additives or compatibility issues in some contexts, the primary reason it’s not suitable is its insufficient resistance to detonation given the engine’s higher compression. The idea that it cannot be pumped or that it’s entirely incompatible isn’t accurate in the same way, since the core mismatch is the fuel’s octane and anti-knock properties.