you need at least a .40 size engine to actually get smoke from the exhaust..its not burned in the fuel, the only thing you can add to fuel would be a couple of ounces of castor oil to a gallon of fuel to add to your exhaust wash.....I once experimented with a cox engine and burned a gas/oil mix (actual gasoline and 2 stroke oil) on a test stand it worked but you have to keep a battery clip on the glow head and I have no idea how long the engine would have lasted but it sure made plenty of smoke in my basement
..maybe I'll try it again out side some time....Rog