Fuel efficiency in a combustion engine is increased by treating the fuel in a reaction chamber prior to delivering the fuel into the combustion chamber of the engine. The method includes the step of entraining a stream of exhaust gas to travel upstream through the reactor chamber in a first flow pattern. The method also includes the step of entraining a stream of fuel to travel downstream through the reactor chamber in a second flow pattern, where at least one of the first and second flow patterns comprises a structured turbulent flow.