What happens if an aircraft reciprocating engine is operated with fuel of a lower grade than specified?

Using fuel of a lower grade than specified for an aircraft's reciprocating engine can lead to significant adverse effects on engine performance. This primarily results in a loss of engine power and efficiency. Lower-grade fuel has a lower octane rating, which can cause the engine to pre-ignite or detonate. Detonation occurs when fuel ignites prematurely in the cylinder, leading to an uncontrolled explosion in the combustion chamber. This can negatively impact the engine's operation and longevity.

Operating with substandard fuel can also affect how well the engine runs, as it may not burn as efficiently as higher-grade fuel. Therefore, the overall performance of the aircraft may be compromised. In severe cases, persistent operation under these conditions could lead to serious mechanical failures or damage to engine components, thereby heightening the risk of failure. Understanding the implications of using the correct fuel grade is crucial for maintaining engine health and ensuring safe operation.