From ComputerCraft Wiki
|Returns how much fuel is inside the specific turtle. Turtles may be configured to ignore the need for fuel via ComputerCraft.cfg, in which case this command will always return "unlimited". Turtles loose their fuel when destroyed, if they don't have a label.|
Trivia: during the 1.4 beta, turtle.getFuelLevel() in softcore (that is now turtleneedsfuel = 0) returned 9000.
|Returns||"unlimited" if fuel is disabled, otherwise the fuel level.|
|Attempts to refuel the turtle if the fuel tank is empty.|
if turtle.getFuelLevel() ~= "unlimited" and turtle.getFuelLevel() < 1 then turtle.refuel() end