A Lycoming IO320 aircraft engine was run on different base fuels containing various percentages of methyl tertiary-butyl ether (MTBE). Vapor lock, vapor to liquid ratio (VLR), and Reid vapor pressure (RVP) tests were performed on the fuel mixtures to obtain a method that will provide a measure of the volatility of aircraft fuels for the purpose of aircraft certification.
For the vapor lock runs the test fuel was heated to temperatures of 32, 38, 44, and 49 degrees Celsius (90, 100, 110 and 120 degrees Fahrenheit). A vapor lock run was performed for each combination of fuel mixture and tank temperature at fuel flow rates of 10, 20, 30, 40, 50 and 60 liters per hour.
The quickest time to vapor lock was found to be at a fuel temperature of 44 degrees Celsius (110 degrees Fahrenheit) at takeoff power. The temperature corresponding to a vapor to liquid ratio of 40 is a good indicator of vapor lock behavior of the fuel since it was found to be approximately equal to the average sediment bowl temperature at vapor lock and linearly related to the average time to vapor lock.