What characteristic makes aviation gasoline suitable for use in reciprocating engines?

The suitability of aviation gasoline for use in reciprocating engines is largely due to its high heat value. This property is crucial because reciprocating engines require a fuel that can produce a significant amount of energy when combusted. A high heat value means that more energy is released from the fuel during combustion, which contributes to the engine's performance, efficiency, and overall power output.

When evaluating the other options, low volatility is typically a characteristic associated with diesel fuels rather than aviation gasoline, as aviation gasoline needs to vaporize efficiently for optimal combustion. Low lead content is significant in modern fuels, especially considering environmental regulations, but does not directly impact the fuel's performance characteristics in terms of energy output. High density could play a role in fuel efficiency and weight considerations, but it is the heat value that directly relates to the combustion characteristics required for effective engine operation.