Abstract: Method of and device for producing electric energy from a cyclic combustion process. The device includes two oppositely disposed aligned spark ignited internal combustion engine cylinders axially spaced from each other, means rigidly connecting the pistons so that they reciprocate in unison in their respective cylinders, and a reciprocable electrical linear generator-motor unit driven by said reciprocatory piston system. The generator-motor unit includes a very light coreless (ironless) coil rigidly attached to and reciprocatory with the piston system, the said coil reciprocating through a constant strength magnetic field. The beginning of the combustion process (or cycle) in each combustion chamber takes place at the lowest possible compression ratio sufficient for the initial ignition of the fuel-air mixture, the combustion process proceeding at a diminishing volume under the pressure from the compression- and combustion-forces of the opposite combustion chamber-piston system.