PURPOSE: To eliminate a discharge gas and exhaust sound in an internal combustion engine and attain a nearly non-pollutive state.

CONSTITUTION: A complex metal solution consisting of iron, aluminum, nickel, cobalt and silicon is mixed with or sprayed into a petroleum-based fuel or an alternate fuel at an arbitrary ratio or a complex metal solution consisting of iron, aluminum, nickel, cobalt and silicon is given to a plant and an extract containing the complex metal is extracted from the plant and the extract is mixed with or sprayed into the petroleum-based fuel or the alternate fuel.