Lava

function RefuelOK()
    turtle.select(1)
    turtle.refuel(1)
    print "Refueling..."
end

function LavaCheck()
    if turtle.getItemDetail(1) ~= nil then
        if turtle.getItemDetail(1).name == "minecraft:lava_bucket" then
            return 1
        end
    else
        return 0
    end
end

function Refuel()
    print "checking fuel..."
    if turtle.getFuelLevel() < 100 then
        if not LavaCheck() then
            print "Not a Lava Bucket"
            return
        elseif LavaCheck() then
            RefuelOK()
        end
    else
        print "fuel okay"
    end
end

Refuel()