Since the engine doesn't have its own supply of oil, it's instead added to the fuel to help lubricate the moving parts and to keep them from burning up. The oil can be castor oil or synthetic oils. Some fuels include a mixture of the two. The oils included in glow fuel are not burned by the engine. Instead, the oil comes out of the exhaust. Not only does the oil lubricate the moving parts, but the oil which comes out the engine helps carry away extra heat.