When motor vehicles switched to using unleaded gasoline, older vehicles had a problem with a recession in the exhaust valve. Eventually, experts were able to work out solutions to this problem. But thinking of this with the recent developments in unleaded aviation fuel, what is the concern about exhaust valve problems occurring in aircraft engines?
Aircraft Engines and Unleaded Fuels
The first thing to remember when comparing aircraft engines to motor vehicles is that they operate quite differently. Aircraft engines are air-cooled and run the exhaust valve at a significantly higher temperature than liquid-cooled engines. Aircraft engines also run at higher loads than automotive engines on cruise conditions. Aircraft are not replaced as often as automobiles and already have hardened valve seats.
Many problems, such as ignition timing and coolant flow, can affect exhaust valve recession. This is why exhaust valve recession is not just limited to large turbo engines.
According to General Aviation News, the question of how aircraft exhaust valves are affected by unleaded gas lies in how long 100LL will be available. Read why Ben Visser, an aviation fuels and lubricants expert and private pilot who worked for Shell for 33 years, says the answer to how long 100LL will be available has the most impact on the protection of aircraft engine exhaust valves.
