What are two functions of tetraethyl lead added to aviation gasoline?

• A. It increases the critical pressure and temperature of the fuel, and it acts as a lubricant for the valves.
• B. It increases the octane rating only.
• C. It reduces combustion temperature.
• D. It acts as a corrosion inhibitor.

Answer: (A)

Tetraethyl lead in aviation gasoline serves two main purposes: it increases the fuel’s octane rating and it provides lubrication for the valve seats and related valve gear. Boosting octane helps the engine resist knocking under high compression, which allows for smoother operation and better performance. The lubrication aspect helps reduce wear on valve seats and stems, especially in older high-compression or high-temperature engines that were designed to run on leaded fuel.

The idea that TEL changes the fuel’s critical pressure and temperature isn’t how it works, so that part of the statement isn’t a functional description of TEL. Among the options, the correct pairing is the one that mentions both an octane boost and valve lubrication.